Farhan Rahmat

Guess Paper (Solved)

Paper-I Theory of Computer Science

Compiled by:

Farhan Rahmat

Farhan Rahmat

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Table of Contents

1.1 Data representation ...................................................................................................................................... 1

1.1.1 Binary systems ........................................................................................................................................ 1

1.1.2 Hexadecimal ........................................................................................................................................... 1

1.1.3 Data storage ......................................................................................................................................... 12

1.2 Communication and Internet technologies ................................................................................................. 13

1.2.1 Serial and parallel data transmission ................................................................................................... 13

1.2.2 Security aspects .................................................................................................................................... 13

1.2.3 Internet principles of operation ........................................................................................................... 13

1.3 Hardware and software ............................................................................................................................... 39

1.3.1 Logic gates ............................................................................................................................................ 39

1.3.2 Computer architecture and the fetch execute cycle ............................................................................ 53

1.3.3 Input devices ........................................................................................................................................ 54

1.3.4 Output devices ..................................................................................................................................... 54

1.3.5 Memory, storage devices and media ................................................................................................... 54

1.3.6 Operating systems ................................................................................................................................ 81

1.3.7 High- and low-level languages and their translators ............................................................................ 85

1.5 Ethics ........................................................................................................................................................... 86

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1.1 Data representation

1.1.1 Binary systems

1.1.2 Hexadecimal

Q1. 1. Express the denary value 109 as

(i) a binary number using an 8-bit byte;

(iii) a hexadecimal number.

128 64 32 16 8 4 2 1

Is

109>=128?

N

Is

109>=64?

Y

Is

45>=32?

Y

Is

13>=16?

N

Is

13>=8?

Y

Is

5>=4?

Y

Is

1>=2?

N

Is

1>=1?

Y

0 1 1 0 1 1 0 1

=109-64 =45-32 =13-8 =5-4 =1-1

=45 =13

=5 =1

=0

=(01101101)2

(iii) a hexadecimal number.

Is 109=128?N

Is

78>=64?

Y

Is

14>=32?

N

Is

14>=16?

N

Is

14>=8?

Y

Is

6>=4?

Y

Is

2>=2?N

0 1 0 0 1 1 1 0

=78-64

=14-8 =6-4 =2-2

=14 =6 =2 =0

=(01001110)2

(ii) a hexadecimal number,

Is 78

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=(93)10

4. Convert the following binary numbers into decimal number & hexadecimal

number:

(i) (00001100)2

(ii) (01011001)2

(iii) (00000111)2

128 64 32 16 8 4 2 1

0 0 0 0 1 1 0 0

0x128 0x64 0x32 0x16 1x8 1x4 0x2 0x1

0 0 0 0 8 4 0 0

=8+4

=(12)10

8 4 2 1 8 4 2 1

0 0 0 0 1 1 0 0

0x8 0x4 0x2 0x1 1x8 1x4 0x2 0x1

0 0 0 0 8 4 0 0

=0 =8+4

=0 =12

=0 =C

=C

=(C)16

(01011001)2

128 64 32 16 8 4 2 1

0 1 0 1 1 0 0 1

0x128 1x64 0x32 1x16 1x8 0x4 0x2 1x1

0 64 0 16 8 0 0 1

=64+16+8+1

=(89)10

8 4 2 1 8 4 2 1

0 1 0 1 1 0 0 1

0x8 1x4 0x2 1x1 1x8 0x4 0x2 1x1

0 4 0 1 8 0 0 1

=4+1 =8+1

=5 =9

=59

=(59)16

(00000111)2

128 64 32 16 8 4 2 1

0 0 0 0 0 1 1 1

0x128 0x64 0x32 0x16 0x8 1x4 1x2 1x1

0 0 0 0 0 4 2 1

=4+2+1

=(7)10

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8 4 2 1 8 4 2 1

0 0 0 0 0 1 1 1

0x8 0x4 0x2 0x1 0x8 1x4 1x2 1x1

0 0 0 0 0 4 2 1

=0 =4+2+1

=0 =7

=7

=(7)16

5. Is there a short cut to working out a binary number that is made of solid ones,

such as: (01111111)2?

127 (=128-1)

128 64 32 16 8 4 2 1

0 1 1 1 1 1 1 1

0x128 1x64 1x32 1x16 1x8 1x4 1x2 1x1

0 64 32 16 8 4 2 1

=64+32+16+8+4+2+1

=(127)10

63(=63-1)

128 64 32 16 8 4 2 1

0 0 1 1 1 1 1 1

0x128 0x64 1x32 1x16 1x8 1x4 1x2 1x1

0 0 32 16 8 4 2 1

=32+16+8+4+2+1

=(63)10

31 (=32-1)

128 64 32 16 8 4 2 1

0 0 0 1 1 1 1 1

0x128 0x64 0x32 1x16 1x8 1x4 1x2 1x1

0 0 0 16 8 4 2 1

=16+8+4+2+1

=(31)10

6. Convert the following Hexadecimal numbers into denary system and binary

system:

(i) A1

(ii) 37

(iii) FF

(iv) 0D

(v) ABC

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1. A1

Binary:

A1-->(10,1)

10 1

8 4 2 1 8 4 2 1

1 0 1 0 0 0 0 1

=(10100001)

2

Decimal: 10 1

16^1 16^0

16 1

=10x16 =1x1

=160 =1

=160+1

=(161)1

0

2. 37

Binary:

37(3,7) 3 7

8 4 2 1 8 4 2 1

0 0 1 1 0 1 1 1

=(00110111)

2

Decimal: 3 7

16^1 16^0

16 1

=3x16 =7x1

=48 =7

=48+7

=(55)10

3. FF

Binary:

FF-->(15,15)

15 15

8 4 2 1 8 4 2 1

1 1 1 1 1 1 1 1

=(11111111)2

Decimal

: 15 15

16^1 16^0

16 1

=15x16 =15x1

=240 =15

=240+15

=(255)10

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4. ABC

Binary:

(A,B,C)(10,11,12) 10 11 12

8 4 2 1 8 4 2 1 8 4 2 1

1 0 1 0 1 0 1 1 1 1 0 0

=(101010111100)2

Decimal:

Q2. When a key is pressed on the keyboard, the computer stores the ASCII

representation of the character typed into main memory.

The ASCII representation for A is 65 (denary), for B is 66 (denary), etc.

There are two letters stored in the following memory locations:

(a) (i) Show the contents of Location 1 and Location 2 as binary. [2]

(ii) Show the contents of Location 1 and Location 2 as hexadecimal. [2]

(b) The following machine code instruction is stored in a location of main memory:

Convert this binary pattern into hexadecimal. [4]

(c) Explain why a programmer would prefer to see the contents of the locations

displayed as hexadecimal rather than binary, when debugging his program that

reads the key presses. [2]

(a) (i) 01000001

01000011 [2]

(ii) 41

43 [2]

(b) FA97 [4]

(c) easier to identify values easier to spot errors [2]

A B C

16^2 16^1 16^0

256 16 1

=10x256 =11x16 =12x1

=2560 =176 =12

=2560+176+12

=(2572)10

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Q3. Electric guitars consist of strings and frets.

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Q4. Digits on an electronic display board can be represented on a 7 5 grid. For

example, the digit 3 is represented as:

Each column in the grid is represented in a computer as a 7-bit register. Five registers

are required to represent the state of the whole digit. The value 1 represents a

shaded square and the value 0 represents an unshaded square. For example, the

digit 3 is represented as:

(a) Show the contents of the five 7-bit registers when representing the digit 9:

(b) In order to prevent errors, an 8-bit register is used. The 8th bit will contain:

0 if the first 7 bits add up to an even number 1 if the first 7 bits add up to an odd number Complete the 8th bit for each register. The first register has been completed for you.

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1.1.3 Data storage

Q5. Give one benefit of storing music files in MP3 format.

(a) Any one from:

file size is small fast to download/upload files format can be played on several types of devices, e.g. mobile phone, CD player, laptop etc. [1]

(b) Describe the type of memory used in MP3 players. [2]

(b) Any two from:

type of EEPROM non-volatile memories solid state memories NAND based memories mini hard disk drives [2]

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1.2 Communication and Internet technologies

1.2.1 Serial and parallel data transmission

1.2.2 Security aspects

1.2.3 Internet principles of operation

Q6. State two advantages and one disadvantage of having a network of

Computers, rather than a series of standalone machines, in a school classroom. [3]

- Sharing of software and data files

- Sharing of hardware, e.g. printers

- Communication

- Security of files more of a problem

(1 per -, max 3) (3)

Q7. (a) State the meaning of

(i) Serial and parallel modes of data transmission. [4]

(ii) simplex and duplex

- Serial is the transmission of data one bit at a time/through one wire

- Parallel is the transmission of data more than one bit at a time/many wires

- Simplex is the transmission of data in one direction only

- Duplex is the transmission of data in both directions simultaneously (4)

Q8. During transmission data can be corrupted. Check sums and parity checks can be

carried out on the data.

(a)Explain how check sums and parity checks are used to detect transmission errors.

-Check sum is the result of adding all the bytes of data (and ignoring the carry out of

the

byte)

-The result is sent along with the data and

-Checked against the total calculated as the data arrives

-If the two totals differ then a transmission error has occurred

-Parity involves every byte having its bits adding to either an odd or even total

-Type of parity must be agreed between sender and recipient

-Use of a parity bit to make each byte the correct type

-If bit is changed during transmission then the sum of bits will not match parity type

(1 per -, max 2 per type of check, max 4) (4)

[4]

(b)Bytes of data transferred using a serial cable are checked for errors at the

receiving end using an even parity check.

Can these bytes of data pass the even parity check?

(a) 01010101 [1]

(b) 11001000 [1]

(c) How can any errors be corrected? [2]

(a) Yes [1]

(b) No [1]

(c) re-reading the byte that was sent request that the byte is resent [2]

Q9. The data which is transmitted between survey sites and head office is liable to errors.

Data which is received is checked for errors.

(a) One method of checking for errors is to use parity checks.

The following four bytes have been received:

01101001 10111100 10101010 00100100

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(i) One of the bytes contains an error. State which byte. [1]

(ii) Explain your choice of answer in (i). [2]

(iii) Explain why a byte may still be in error even if it passes the parity test.

[1]

(b) A second method of checking for errors is to use check sums.

Explain how check sums are used to check data for transmission errors. [4]

(a) (I)10111100/the second one [1]

(ii)- This has an odd number of ones

- The others all have an even number of ones

- Even parity is being used

(1 per -, max 2) [2]

(iii)- There may be two (or an even number of) errors in one byte [1]

(b) - data bytes are added together

- MOD 256

- Result (Check Sum) is sent with data

- Calculation redone at receiving end

- Results compared

(1 per -,1st +conditional 3, max 4) [4]

Q10. (a) Define the term protocol.

-Set of rules...

-to control the transmission of data [2]

(b) Explain hypertext transfer protocol (http). [2]

Short for HyperText Transfer Protocol, the underlying protocol used by the

World Wide Web. HTTP defines how messages are formatted and transmitted,

and what actions Web servers and browsers should take in response to

various commands

Q11. (a) State two differences between a local area network (LAN) and a wide area

network(WAN). [2]

LAN over short distances/buildings/site // WAN geographically remote LAN uses own communication medium/WAN uses third party LAN more secure/WAN more open to attack (1 per , max 2) [2]

(b) State what is meant by each of the following types of data transmission. Give

an advantage of each.

(i) Serial Individual bits sent one after another/along single wire

can be used over long distances Less chance of corruption/less chance of bits having order changed [2]

(ii) Parallel [4] a byte is sent simultaneously / at the same time along 8 wires Much faster transmission rate [2]

(c) The following bytes were received during a data transmission.

01101101 10101010 10111101 10110001

Parity is being used as an error check.

State which one of the bytes has been corrupted. Explain why you chose the

one that you did. [3]

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Parity is being used as an error check. State which one of the bytes has been corrupted. Explain why you chose the one that you did. Corrupted byte Reason [3]

Q12. (a) Give one effect of hacking. [1]

One effect from

fraud/transferring money

viewing sensitive confidential data

changing data

selling data

virus/logic bomb

blackmail

loss of data/file

misuse + qualification [1]

(b) Give two ways of protecting computer systems against hacking. [2]

(b) Two ways from

passwords/codes

encryption

monitoring attempts to access the system/logging use

lock keyboard/computer/doors

firewalls

smart card

fingerprints/biometrics

do not read emails from unknown sources

USB security device [2]

Q13. Many bank customers now bank on-line using the Internet.

(a) State two advantages for the bank of on-line banking. [2]

(a) Two advantages for the bank from

less staff/employment costs/queues in the bank

can close branches/less costs for maintaining branches

less paper/electronic transactions/less cheques/less cash/no cheques/no cash

new international customers [2]

(b) State two disadvantages for a bank customer of on-line banking. [2]

(b) Two disadvantages for the customer from

need to have/be able to use devices capable of accessing the internet

cannot have the personal service offered by the conventional bank

cannot get cash/cannot put in cash

insecure/security risks/fraud/hacking

cost of ISP/phone bill

if there is no broadband then the phone lines are tied up [2]

(c) Give two advantages to customers of using Internet banking. [2]

(c) Any two from:

no time wasted travelling to the bank

easier/faster to manage accounts

no money spent on travelling expenses going to bank

no embarrassment asking for loans face to face with a manager

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possible to still bank even when banks closed/can bank 24/7

dont have to wait for post/immediate payments can be made disabled people dont have to travel to a bank less chance of being robbed for cash [2]

(d) Give two disadvantages to customers of using Internet banking. [2]

(d) Any two from:

hackers can intercept data/risk of fraud

no personal touch

customers can easily mis-manage their accounts

increase in phone bills

without broadband, ties up the phone line

increased risk of losing personal data [2]

Q14. A company has set up an Internet website to sell their electrical goods online.

(a) Give two features you would expect to see on the website. [2]

(a) Any two from e.g.: electronic checkout shopping basket ability to track status of order on line secure buying using credit cards when customer bought X, they also bought Y facility search facilities for items recognise customers as soon as they log on drop down boxes to choose categories sales confirmation by automatic email save customer details/customised pages online help facility hyperlinks to other pages ability to bookmark/tag page(s) [2]

(b) Payments for goods can be made by credit/debit cards. Data from the cards is

encrypted.

(i) What is encryption?

(ii) Why is data encrypted? [2]

(b) (i) Any one from: process of changing/scrambling/encoding data into a meaningless form use of software/algorithms to turn data into a meaningless form [1] (ii) Any one from: to avoid data being read/understood by hackers/unauthorised people to protect sensitive data from unauthorised people [1]

(c) Apart from credit card fraud, people have other fears about buying from the

Internet.

Describe one of these fears. [1]

(c) Any one from: viruses being downloaded from the site bogus/fake sites unwanted sites/porn sites coming up when searching unsolicited mail cookies (etc.) being stored on hard drive (spying software) hacking [1]

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Q15. To log on to a computer, a user needs to type in a user id followed by a password;

these should match up.

(b) Sometimes it is necessary to key in the password twice.

Name this type of data check. [1]

(b) verification [1]

Q16. FIVE security or data loss issues are shown on the left hand side.

FIVE possible methods of data recovery or protection are shown on the right.

Match the definitions/descriptions on the left to the most appropriate method on the

right by drawing connecting arrows.

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(b) Five security or data loss issues are shown on the left-hand side.

Five possible methods of data recovery or protection are shown on the right.

Draw a line to match each definition/description of Issues to the most appropriate

Methods of Data Recovery.

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Q17. Describe THREE ADVANTAGES and TWODISADVANTAGES to the general public of

using the Internet to do online shopping. [5]

Any three advantages from:

can shop 247/in own time worldwide therefore greater choice no need to waste money on travelling to shops no need to waste time travelling disabled/elderly people dont have to leave their homes cost savings often passed on to customer can look for best value in a short time less pollution since fewer car journeys Any two disadvantages from:

shops close down in cities/unemployment/ghost towns increased risk of fraud/hacking less social interaction between people cant see the goods first goods may not arrive/bogus web sites environmental issues/wasted packaging ties up the phone line if broadband not available increase in phone bills [5]

Q18. A company selling CDs uses a unique 6-digit identification number for each CD title.

The right-most digit (position 1) is a check digit.

For example,

The validity of the number and check digit is calculated as follows:

multiply each digit by its digit position add up the results of the multiplications divide the answer by 11 if the remainder is 0, the identification number and check digit are valid (a) Show whether the following identification numbers are valid or not. You must

show how you arrived at your answer.

(i) 4 2 1 9 2 3

working:

valid or not valid?

(ii) 8 2 0 1 5 6

working:

valid or not valid? [3]

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(b) Find the check digit for the following identification number:

5 0 2 4 1 __

working:

check digit: [2]

(c) Describe, with examples, two different types of data entry errors that a check

digit would detect. [2]

Q19. (a) What is meant by the term web browser? [1]

(a) program/software that allows a user to display web pages, web sites, etc. NOT access the Internet

(b) Rock-ICT has set up a website as shown below:

Give the names of the three parts that have been labelled: [3]

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(b) (i) webpage (part of)

(ii) radio button

(iii) hyperlink NOT link

(c) How does the website recognise the users buying preferences as soon as they visit the website? [1]

(c) reference to cookies or description of cookie

(d) Hacking is one security issue associated with the Internet and emails.

State two other security issues. [2]

Q20. A computer system is to have wireless access (Wi-Fi) to the Internet.

(a)State five potential security issues. [5]

Any five from:

viruses hacking cookies pharming phishing spyware tapping into unsecured wifi network/war driving shoulder surfing/over-the-shoulder observation of the Internet users credentials/user name

and password [5]

(b) Ahmed uses the Internet for some time and is puzzled by the terminology.

Draw a line to match each description to the appropriate technical term.

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(c) Ahmed sees the message Set your browser to accept cookies. Explain why some websites make this request. [2]

(c) any two from:

to enable logon information to be kept on his computer to provide pages customised for Ahmed the next time he logs on to implement shopping carts and one-click purchasing to be able to distinguish between new and repeat visitors to the website [2]

Q21. Describe meaning of SSL?

Organizations that use the Web to collect and transmit sensitive data to customers

or other organizations need to secure their Web site. The general standard is the use of secure socket layers (SSL), which encrypts data transmitted via a Web site

Q22. Describe ARQ & FEC.

Error correction may generally be realized in two different ways:

Automatic repeat request (ARQ) (sometimes also referred to as backward error

correction): This is an error control technique whereby an error detection scheme

is combined with requests for retransmission of erroneous data. Every block of

data received is checked using the error detection code used, and if the check

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fails, retransmission of the data is requested this may be done repeatedly, until the data can be verified.

Forward error correction (FEC): The sender encodes the data using an error-

correcting code (ECC) prior to transmission. The additional information

(redundancy) added by the code is used by the receiver to recover the original

data. In general, the reconstructed data is what is deemed the "most likely"

original data.

Q23. In each case below, state which Internet term is being described.

(a) Malicious software installed on a users hard drive or a web server; the software re-directs the user to a fake website without their consent or knowledge. [1]

(b) Personal Internet journals where a writer enters text about a certain topic;

anyone can comment on the topic. [1]

(c) Websites designed to promote the building of online communities who share the

same interests; usually free of charge; users can add friends, post messages to each

other and update personal profiles. [1]

(d) Legitimate-looking email sent to a user in the hope of gathering personal

information; as soon as the recipient clicks on the link in the email (or email

attachment) they are sent to a fake website. [1]

(e) Software that secretly gathers information by monitoring key presses on a users keyboard; this information is relayed back to the person who sent the software

originally. [1]

(a) pharming

(b) blog(s) [1]

(c) social networking (sites) [1]

(d) phishing [1]

(e) spyware/key logging (software) [1]

Q24. A music club keeps its members details on a computer file.

(a) Complete the table below which shows the data type, field length and

validation check used for the club members data.

Q25. Explain, using examples where appropriate, the following computer terms:

(a) verification

(b) validation

(c) phishing

(d) pharming

(e) DOS

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(f) spyware

(g) tapping into wireless networks

(a) Verification

any two points from:

check on input for errors

on screen checking/checked by human

comparing input/use of second operator/by double entry

examples: password entry, email entry [2]

(b) Any one point from:

computer check on input data check data is wrong/correct = 0

detects any data which is incomplete or not reasonable

(ii) Describe one type of validation check.

(ii) Any one point from:

length check e.g. only 30 characters in name field

character check e.g. name doesnt contain numeric chars

range check e.g. day of month in date is between 1 and 31

format check e.g. date in the form xx/yy/zz

check digit e.g. end digit on bar code to check if it is valid

type check e.g. integer, real

(presence check = 0)

(c) Phishing refers to emails that trick people into giving out their personal and

banking information; they can also be sent by SMS. These messages seem to come

from legitimate businesses, normally banks or other financial institutions or

telecommunications providers. The scammers are generally trying to get information

like your bank account numbers, passwords and credit card numbers, which they

will then use to steal your money.

(d) Pharming is when you are redirected to a fake/scam version of a website which

may look identical to the website you were trying to view. This is sometimes referred

to as page-hijacking or page-jacking. In this scam, the legitimate url you typed into

your browser or the bookmarked link you followed automatically changes and

redirects you to a fake address, often which looks very similar to the legitimate

address.

(e) DoS stands for Denial of Service. A malicious hacker uses a DoS attack to make a

computer resource (i.e. website, application, e-mail, voicemail, network) stop

responding to legitimate users. The malicious hacker does this by commanding a

fleet of remotely-controlled computers to send a flood of network traffic to the

target. The target becomes so busy dealing with the attackers requests that it

doesnt have time to respond to legitimate users requests. That can cause the

target system to stop responding, resulting in long delays and outages.

(f) Spyware is a software that monitors key presses on a users keyboard, and relays

the information back to the person who sent the software.

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Q26. (a) Give two examples of computer crime. [2]

(b) Describe two methods used to prevent computer crime. [2]

(c) Describe ways to guard against each of the following Internet security issues. (A

different method should be given in each case.)

1. viruses

2. hacking

3. spyware

4. phishing

5. tapping into wireless networks [5]

(c) viruses e.g.

use anti-virus software // regular virus scans

dont open/use disks // dont open email attachments from unknown sources

Hacking e.g.

passwords / user IDs

firewalls

Spyware e.g.

anti-spyware software

delete cookies at end of session

Phishing e.g.

dont open emails from unknown sources

dont divulge personal information via email / unsecure website

ensure that the site viewed has a valid security certificate (SSL)

tapping into wireless networks e.g.

secured wifi network (protected by passwords)

encryption / WEP

no broadcast of network ID [5]

Q27. State three effects on society due to the increase of businesses using e-commerce.

Any three effects from:

loss of jobs

traditional shops/banks close

city/town centres become deserted as shops/banks close

gap between rich and poor grows (rich get access to savings by shopping

online)

less interaction between people

increase in small businesses

less pollution/less need to travel

security fears

people will need credit cards/bank accounts/computer systems [3]

[3]

Q28. (i) Name one method used to protect data against unauthorised access. [1]

(i) Any one from:

passwords/biometrics

user id/access rights

firewall

removable storage media

physical protection [1]

(ii) Name one method used to protect data in a file from being understood

when an unauthorised person has gained access to the file. [1]

(ii) encryption [1]

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Q29. A company is concerned about three aspects of the security of data stored in

computer files:

data corruption data loss illegal access to data For each of the above, give one reason why it could occur and state one method

of prevention. Your reasons must be different in each case. [6]

Q30. (a) State three reasons why a computer system failure might occur (malfunction).[3]

(a) Any three from: glitches in the software e.g. divide by zero software conflicts virus operating system software loss/corruption hardware malfunction (e.g. overheating of circuit board, processor fans failing etc.) hardware incompatibility power supply interruption/spikes incorrect power down after use hard disk crash/failure [3]

(b) One effect of a computer system failure is the loss or corruption of files. State one

way of recovering a file if it has been lost or corrupted. [1]

(b) Any one from:

Grandfather-Father-Son (GFS)/file generation system backups parallel systems type/scan and OCR in new data again from the hard copies [1]

(c) How is it possible to ensure illegally accessed files are unreadable? [1]

(c) Any one from:

encryption encrypt files [1]

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Q31. A college secretary inputs data into fields on a computer screen as shown below:

(a)Choose a suitable different validation check for each of the following:

(i) Student Sex which can be M or F only

(ii) Todays Date which must be written as, for example, 15/10/2010

(iii) the Examination Result which can be any number from 0 to 100

EACH RESPONSE MUST BE DIFFERENT

(a) (i) Any one from: character/type check length check Boolean check presence check (ii) Any one from: format check character/type check length check presence check (iii) Any one from:

range check character/type check presence check

(b) Apart from validation, how would it be possible to ensure only certain data could

be input into each of the fields on the computer screen? [1]

(b) Any one from: drop down lists showing M or F only, possible dates, etc. use of touch screens with only certain data options use of restricted lists radio buttons [1]

(c) The secretary takes a ten minute break every hour.

(i) Apart from switching off, how can the secretary make sure the computer system is

secure whilst she takes a ten minute break?

(ii) From a health and safety aspect, why does the secretary need to take regular

breaks? [2]

(c) (i) Any one from: lock computer log off the system if in an office, lock the door put into sleep/hibernate mode with password [1] (ii) Any one from: to prevent RSI to prevent neck/back problems possible to prevent eye sight problems/headaches [1]

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Q32. Which validation methods are being carried out by the following three pseudocode

statements?

(i) ifage > 10 and age < 20 then print "correct"

(ii) ifgender = "male" and title = "Mr" then print "correct"

(iii) iffield = "" then print "input data is missing"

(a) (i) range check

(ii) consistency check / crossfield check

(iii) presence check [3]

(b) Name a different validation technique and give an example to show how it

works.

(b) 1 mark for name and 1 mark for example. Example must match name

Name Example

type/character check only letters typed into name field

format check ensure date typed in correct format

length check ensure year field has four digits

check digit on barcodes to ensure they have been read correctly

Q33. A hospital holds records of its patients in a database. Four of the fields are:

date of visit (dd/mm/yyyy)

patients height (m)

8-digit patient ID

contact telephone number

The presence check is one possible type of validation check on the data. For each

field, give another validation check that can be performed. Give an example of

data which would fail your named validation check.

A different validation check needs to be given for each field.

Field Name Name of validation check

Example of data which

would fail the validation

check

Date of visit

Patients height

Patient ID

Contact

telephone

number

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Q34. The diagram below shows a number of descriptions and terms used in computer

security.

By drawing arrows, connect the correct description to the computer security term.

Program installed.

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Q35. The following five statements about Internet security are incomplete:

(i) Illegal access to a computer system is known as < - - - - (a) - - - - >.

(ii) < - - - - (b) - - - - > are programs that self-replicate (copy themselves) and are

designed to disrupt computer systems.

(iii) < - - - - (c) - - - -> is where a user is sent legitimate-looking emails; as soon as the

email is opened and the recipient clicks on the embedded link, they are sent to a

fake website.

(iv) Software that monitors key presses on a users keyboard, and relays the

information back to the person who sent the software, is known as < - - - - (d) - - - - >.

(v) < - - - - (e) - - - - > is malicious code or software installed on the hard drive of a

users computer or on a web server; the code or software will re-direct the user to a

fake website without their knowledge.

Complete the five statements using words from the following list:

cookies

hacking

pharming

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phishing

spam

spyware

viruses

web browsers

(a) ....................................................................................................................................... [1]

(b) ....................................................................................................................................... [1]

(c) ....................................................................................................................................... [1]

(d) ....................................................................................................................................... [1]

(e) ....................................................................................................................................... [1]

(a) hacking [1]

(b) viruses [1]

(c) phishing [1]

(d) spyware [1]

(e) pharming [1]

Q36. (a) Felipe wrote down the following three statements.

In each case, indicate whether the statement is true or false and give a reason for

your choice.

encrypting data prevents it from being hacked TRUE/FALSE ............................................................................................................................

Reason .....................................................................................................................................

backing up data removes the risk of the data being infected by viruses TRUE/FALSE ............................................................................................................................

Reason .....................................................................................................................................

wireless (WiFi) networks are less secure than hard-wired systems TRUE/FALSE ............................................................................................................................

Reason ................................................................................................................................ [3]

(a) FALSE encryption only stops data being read / making sense (but does not prevent the act of hacking)

FALSE data when backed up could still have the virus attached to it when the backed up data is re-loaded at a later date, the virus could be loaded again into the system together with the stored data

TRUE tapping into a Wi-Fi network is relatively easy (even when the network is protected by passwords)

1 mark for each correct TRUE / FALSE with correct corresponding reason [3]

(b) Felipe uses Internet banking. When he logs on, the website asks for the 1st,

4th and 8th characters in his password. He selects the characters from drop-down

boxes.

(i) State why drop-down boxes are used. [ 1]

(ii) Felipe is also asked to confirm the last date and time when he logged onto the

website.

State why he is asked to confirm this. [1]

(iii) When Felipe wishes to return to a previous page on this website, he clicks on the

View My Account option rather than using the browser arrows. If he uses the browser

arrows, he is logged out of the website.

Give a reason why the website does this. [1]

(b) (i) drop down boxes help defeat spyware / key logging software

[1]

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(ii) to ensure that it was in fact Felipe who logged on last time [1] an additional authentication check (iii) in case it is not Felipe who attempts to access the account [1]

Q37. Data sent across the Internet are frequently encrypted. The following flowchart

shows a basic encryption method (Note: the symbol in the flowchart means is replaced by).

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(c) Any three from:

customers need a password / PIN use of card readers / use of Transaction Authentication Number (TAN) only certain characters from password / PIN requested the requested characters change each time user logs on card security code requested

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use of drop down boxes use of a customer reference number inform customer when they last logged on to the website use of image verification code e.g. CAPTCHA make reference to something unique to the customer e.g. their mobile phone number

use of secure protocol e.g. https, padlock symbol [3]

Q38. In a simple symmetric encryption system, each letter of the alphabet is substituted

with another.

The plain text message:

The quick brown fox jumps over the lazy dog.

becomes the cypher text message:

Zag towns jumpy dmh coilp mngu zag bfke qmx.

(a) (i) Decode this cypher text message.

Agbbm Pmubq [2]

(ii) Convert these words to cypher text.

Computer Science [2]

(b) Both the person who sends the message and the person who receives it need to

know what the substitution key is, and they need to keep this secret. A copy of the

substitution key has been sent using SSL transmission.

Explain why this keeps the copy of the key secret during transmission. [2]

(a) 1 mark for each correct word

(i) Hello World [2]

(ii) Nmilozgu Pnwgyng [2]

(b) use of Secure Socket Layer the key itself is encrypted using strong encryption [2]

Q39. Can you decipher this code? Here's a hint: Z=A; +=1; ~=10. Enter the message in the

space below. Try to figure out the code without using the decryption tool for every

letter. Can you think of a faster or easier way to solve this puzzle?

THE CENTRAL INTELLIGENCE AGENCY WAS CREATED IN 1947 WHEN PRESIDENT

TRUMAN SIGNED THE NATIONAL SECURITY ACT.

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Q40. No need for a decoder. Just pick out every third letter!

Use all CAPITAL letters when entering your answer.

GENERAL DONOVAN IS CONSIDERED THE FATHER OF MODERN AMERICAN

INTELLIGENCE GATHERING.

Q41. Can you decipher this code? Here's a hint: 11 = A; 10 = Z. Enter the message in the

space below.

THE CIA IS LOCATED IN LANGLEY, VA.

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1.3 Hardware and software

1.3.1 Logic gates

Q42. A car has an engine management system (EMS). The EMS outputs the following

signals.

(a) (i) Draw a logic circuit for the following fault condition:

All three signals (A = 1, B = 1 and C = 1) indicate a fault. The driver is warned to stop

the engine output X = 1.

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(ii) Draw a logic circuit for the fault condition:

Either (A = 1 and B = 1) or (B = 1 and C = 1) indicate a fault. The driver is warned that

the engine needs a service output Y = 1.

(iii) Draw a logic circuit for the fault condition:

Either A = 1 or B = 1 or C = 1 indicate a fault. A red warning light shows up on the

dashboard output Z = 1.

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Q43. Complete the truth table for the following logic circuit:

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(b) Draw a logic circuit corresponding to the following logic statement:

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Q44. (a) Draw the logic circuit corresponding to the following logic statement:

X = 1 IF ( (A is NOT 1 AND B is 1) OR (B is 1 AND C is 1) ) OR (C is 1)

[5]

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(b) Complete the truth table for the above logic statement:

[4]

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Q45. Complete the truth table for the following logic circuit:

(b) Re-draw the logic circuit shown opposite, using NAND and NOR gates only. [2]

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(c) Write a logic statement that describes the following logic circuit:

[3]

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Q46. Complete the truth table for the following logic circuit:

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(b) Write the logic statement to describe the following logic circuit:

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47. (a) (i) Complete the truth table for the logic circuit which is made up of NAND gates

only.

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Q48. A power station has a safety system based on three inputs to a logic network. A

warning signal (S = 1) is produced when certain conditions occur based on these 3

inputs:

A warning signal (S = 1) will be generated if:

either (a) Temperature > 120C and Cooling Water < 100 l/hr

or (b) Temperature < 120C and (Pressure > 10 bar or Cooling Water < 100 l/hr)

Draw a logic network and truth table to show all the possible situations when the

warning

IF (T=1 AND W=NOT 1) OR (T=NOT 1) AND (P=1 OR W=NOT 1) THEN S=1

Q849 A chemical plant gives out a warning signal (W = 1) when the process goes wrong. A

logic network is used to provide input and to decide whether or not W = 1.

A warning signal (W = 1) will be generated if

either (a) Chemical Rate < 10 m3/s

or (b) Temperature > 87 C and Concentration > 2 moles

or (c) Chemical rate = 10 m3/s and Temperature > 87 C

Draw a logic network and truth table to show all the possible situations when the

warning signal could be received.

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1.3.2 Computer architecture and the fetch execute cycle

Q50. (a) Describe what is meant by Von Neumann architecture. [3]

(b) Explain the purpose of each of the following special registers in a processor.

(i) Program Counter (Sequence Control Register). [2]

(ii) Current Instruction Register. [2]

(iii) Memory Address Register. [2]

(iv) Memory Data Register. [2]

(v) Accumulator

(a) Program is stored in memory

along with data

programs and data are indistinguishable

Uses a single processor

Sequential carrying out of instructions

(1 per point, max 3) (3)

(b) (i) Contains the address of the

next instruction to be carried out

Controls the sequence of instructions

(ii) Holds the instruction

while it is being executed

Contains both function and address/operand

(iii) Holds the address of the

instruction/data

that is next to be used

(Must have first mark point before any credit)

(iv) Contents of any address that has been accessed

are placed in here first before being used

May be an instruction or a piece of data

OR:

Holds data/instructions

When being passed between memory and CPU/acts as a buffer

between memory and CPU

(v) Stores results of calculations/does the arithmetic

All input to and output from processor pass through the accumulator

(1 per point, max 2 per dotty, max 10) (10)

Q51. (i) Explain what the accumulator holds and how the contents change

during the fetch-execute cycle. [2]

(ii) Explain what the program counter (PC) holds and how the contents

change during the fetch-execute cycle. [3]

(i) -Hold the data currently being processed

-Result of calculation is held in accumulator...

-before being passed to memory unit

(1 per -, max 2) [2]

(ii) -The address of the next instruction

-Contents incremented (after being read)

-Contents changed by a jump instruction

(1 per -, max 3) [3]

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1.3.3 Input devices

1.3.4 Output devices

1.3.5 Memory, storage devices and media

Q52. (i) What information would be stored on the bar code? [1]

(ii) Why do airports use the bar codes on baggage? [1]

(f) (i) any one from:

passenger name/passenger ID

destination(s)/point of departure

flight id [1]

(ii) any one from:

tracking/uniquely identifies baggage/ensures baggage gets to right place

increased security

links to passenger/ensures luggage cannot travel without passenger [1]

Q53. Name two devices used for direct data capture. Give one application for each

device named. [4]

Q54. An interactive information system is being designed for use in the terminal building of

an airport.

(a) (i) State an input device which would be suitable for use in this

application.

Justify your choice. [2]

(ii) State an output device which would be suitable for use in this

application.

Justify your choice. [2]

(a) (i) -e.g. Touch screen

-because it has limited options / is a simple user interface

-acts as both an input and an output [2]

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(ii) -e.g. screen / speaker

-To show directions / to see the options

-Output sound warning for incorrect input / verbal instructions [2]

Q55. A supermarket uses barcodes as part of its item price retrieval and automatic stock

control system.

A customer takes items to the point-of-sale (POS) checkout. The barcodes are

scanned.

(a) Describe what happens next regarding data retrieval and stock control. [5]

(b) Name two devices needed at the POS checkout.

Give a reason for your choice of device. [4]

(a) Any five points from:

if the barcode cant be read, the number is keyed in using a keyboard the barcode is the key field in the stock file

the barcode is searched for in the stock file

until a match is found

(if no match, error message sent back to POS)

If match found, the appropriate record is accessed

the price + description of goods is sent back to the POS terminal

the stock level in the record is found and 1 is subtracted for each item

bought/scanned

the new stock level is written back to the file

if stock level

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device 2

use [4]

(b) 1 mark for each device + 1 mark for correct matching use

device: beeper/loud speaker

use: to indicate barcode correctly read/error in reading barcode

device: (LCD) screen/monitor

use: to show prices and other information about goods

device: touch screen

use: to show prices and other information about goods/to select items that

need to be weighed/identified

device: weighing machine

use: to find weight of loose items (e.g. fruit) to enable pricing

device: (magnetic) card reader/CHIP and PIN reader

use: to read customers debit/credit card/enable customer to pay for goods using a credit or debit card

device: printer

use: to print receipts

(NOT keypad) [4]

Q57. Items sold in supermarkets are all marked with bar codes.

(a) Customers are given an itemised bill at the checkout. Give two advantages to

the customer. [2]

(b) Give two ways the information on the bar code can be input at the checkout.

[2]

(c) Describe how bar codes are used in automatic stock control. [3]

(a) Any two advantages from:

know prices of each item/check errors

proof of purchase

can check totals themselves

can check items [2]

(b) Any two ways from:

using bar code reader/scanner/wand/gun to read bar code

key in/type in/enter manually the number under the bar code

laser = 0

light pen = 0 [2]

(c) Any three points from:

bar code read

item identified on the file

number of items reduced by 1 each time item is sold

when new item come in/returned stock level increased by 1

minimum stock level stored on file

if stock level less than minimum/reorder level automatic re-ordering done alert that stock low = 0 [3]

Q58. Describe the difference between speech recognition and speech synthesis. [2]

3 Two points one from each group:

speech recognition is a form of input;

speech recognition requires a microphone;

speech recognition is an example of an expert system

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speech synthesis is a form of output

speech synthesis requires speakers

in speech synthesis words are chosen from a database [2]

Q59. Describe three ways you could modify a typical input/output environment to

enable people with disabilities to use the computer system. [3]

Any three points from: (NB if disability mentioned, shouldnt conflict with method/device)

large/concept keyboards/switches

braille keyboards (for partially sighted/blind)

tracker ball to move pointer if keyboard/mouse cant be used touch screens (using head wands)

software to predict words (e.g. for dyslexic people)

speech recognition

foot activated control (if no arm movement)

large icons/fonts on screens ( if partially sighted) braille printers

speech synthesis speakers = 0

large screen

choice of colours [3]

Q60. A supermarket makes use of barcodes on all its goods as part of its automatic stock

control system.

(a) Describe how the price is found for each item sold. [2]

(b) The following are steps in the automatic stock control system.

Number the steps in the correct order.

[4]

(a) Any two points from:

barcode is scanned/keyed in barcode is validated (by check digit) system looks up barcode in computer files/database retrieves (and returns) price [2]

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Q61. A factory uses a computer system to store information about customers, spare parts

and general administration.

(a) Spare parts can be identified by selecting from diagrams on a computer screen.

Describe what hardware would be needed to allow the parts to be selected in this

way. [2]

(b) The factory needs to buy a new printer. It has decided to buy either a dot matrix

printer or an inkjet printer. Discuss the advantages and disadvantages of using both

types of printer in this application. [3]

(a) Any two correct input devices

OR input device + correct type of screen

mouse/trackerball + CRT screen/TFT screen touch screen + CRT screen/TFT screen light pen + CRT screen [2] (b) Dot matrix printer:

Accept a max of 2 advantages and a max of 2 disadvantages:

Advantages:

suitable for dirty/dusty/damp atmospheres cheap to maintain cheap to run can operate with continuous/multipart stationery Disadvantages:

poor print quality very noisy very limited colours [3] Inkjet printer:

Accept a max of 2 advantages and a max of 2 disadvantages:

Advantages:

inexpensive to purchase high quality printouts can use colours supported by most operating systems quiet Disadvantages:

run out of printing ink quickly/cartridges run out quickly price per page/inks are expensive not suitable for dirty/dusty/damp atmospheres [3]

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Q62. The following table shows three applications which require specialist output devices.

For each application, suggest one possible output device and give a reason for your

choice.

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Q63. A list of four printers and four different applications which use printers is shown below.

(a) Using arrows, link each printer to the most appropriate application.

(b) Give one feature of each printer which makes it appropriate for the application.

3D printer

Dot matrix printer

Colour inkjet printer

Colour laser printer [4]

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Q64. For each of the following five groups of hardware items, write down a computer

application that would need those items.

Q65. (a) An airport uses electronic devices as part of its security systems.

One system matches the face of a passenger with the photograph in their

passport.

What two input devices would be needed to do this? Give reasons for your

choice of

device. [4]

(b) When the passenger goes to the check-in desk, their luggage is weighed.

(i) How does the computer system capture the luggage weight? How

does it Then check that it does not exceed the airlines weight limit?[3] (ii) The computer also prints out a label identifying passenger ID, flight

number and destination. This label, which is tied onto the luggage, is

computer readable.

Describe a suitable data capture system which could be used to read

these labels so that the luggage can be tracked. [2]

(a) 1 mark for name of device + 1 mark for reason

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scanner

to produce an electronic/digital map version of the passport photograph

(scans) into computer readable format

digital camera/video camera

to produce an electronic image of the passengers face produces a similar format to the scanned image [4]

(b) (i) 1 mark for each point

use of a pressure sensor

sends data back to computer system

need for conversion to digital form (ADC)

computer calculates weight based on sensor data

this calculated value is compared / (or equivalent) to stored values

sends weight back to a small screen at check-in

if weight exceeds airline limit, operator warned at check-in by, e.g., a

flashing screen or

beeping sound / if weight below limit luggage accepted [3]

(ii) 1 mark per point

(labels printed in form of) a barcode

barcode is unique

use of barcode reader/scanner

barcode is used as a key field in passenger record

barcode read at each stage .. ... and this data is stored in passenger record

thus allowing tracking/whereabouts of luggage at any stage [2]

Q66. Name a suitable hardware device to enable automatic data capture in each of the

following applications. Each device must be different.

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Q67. The following diagram shows six descriptions of automatic data capture methods

and six terms.

Draw lines to connect each description to the correct term.

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Q68. (a) State two differences between random access memory (RAM) and read only

memory(ROM). [2]

(b) Describe what is stored on

(i) RAM,

(ii) ROM

explaining why that type of memory is appropriate. [4]

(a)-ROM cannot be altered, RAM can.

-ROM is not volatile, RAM is.

-ROM is normally smaller capacity than RAM

(1 per -, max 2) [2]

(b) (i) RAM,

-Data in use/software in use/ part of operating system

-Processor can only use what is stored in RAM/not needed for long [2]

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(ii) ROM

-Bootstrap/boot loader/loader/startup program

-It must be available when the computer is switched on/must not be

altered [2]

Q69. Name THREE different types of storage media and give an example of each.

Q70. A company produces animation effects using computers rather than producing

them manually.

(b) Each image takes about 400 kilobytes of storage. 25 images per second are

produced.

How much memory would be needed to store a 30-minute animation?

Q71. Juan uses a company which offers the following

Internet broadband transfer rates:

56 megabits per second DOWNLOAD 16 megabits per second UPLOAD (b) If each music track is 3.5 megabytes in size, how long would it take Juan to

download his 40 tracks?

(Show your working.)

(c) He has decided to upload 36 photographs onto his social networking website.

Each photograph is 1.8 megabytes in size.

How long wo uld it take to upload his photographs?

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Q72. (a) John has bought a 4 Gbyte MP3 player.

(You may assume: 1 byte = 8 bits, 1 Mbyte = 1024 kbytes and 1Gbyte = 1024 Mbytes)

(i) We can assume that each song lasts 3 minutes and is recorded at 128

kbps(kilobits per second).

How much memory is required per song? [2]

(ii) Using your answer in (i), how many songs can be stored on Johns MP3 player?[2] (b) John also bought a device for recording television programmes. It allows him to

record a programme at the same time as he is watching an earlier recording.

Describe how such a system would work. [3]

Q73. The doors on a train are opened and closed automatically. Motors are used to

operate the doors.

The system is controlled by a microprocessor.

Each door has a sensor which detects if a passenger enters or leaves the train as the

doors are closing. If a passenger is detected, the doors are automatically re-

opened.

(a) Name a sensor which could be used to detect a passenger. [1]

(b) If the sensor in one of the doors fails, describe a safety mechanism to prevent

injury to a passenger. [1]

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(c) Describe how the sensors, microprocessor and door motors interact to ensure a

passenger is not trapped in a closing door. [4]

(a) Any one from:

infra red (sensor) pressure (sensor) proximity (sensor) [1]

(b) Any one from:

additional sensors used door defaults to open position sounds an alarm if a sensor fails [1]

(c) Any four points from:

sensors continuously send signals/data sensor sends signals/data sent to the microprocessor signal converted to digital if necessary (using ADC) microprocessor checks which door(s) is (are) affected microprocessor compares sensor reading with stored values if reading indicates passenger detected microprocessor sends signal/data to actuators/motor (converted to analogue using DAC) to operate motors to open doors microprocessor also send signal to drivers cab (automatically) to sound an alarm monitoring continues until system switched off [4]

Q74. Data-logging is used for monitoring the level of oxygen in a river.

(a) State one item of hardware that is used to collect the oxygen data. [1]

(b) Explain how the oxygen data is processed by the computer. [2]

(c) State two ways that the oxygen data could be displayed for a user to

understand. [2]

(d) Explain what the computer would do if the amount of oxygen in the water is too

high. [1]

(e) Give two advantages of using data-logging for monitoring the oxygen data in a

river. [2]

8 (a) One item from

probe/sensor, oxygen sensor/gas sensor

AD converter [1]

(b) Two from

AD converter (if not awarded in (a))

sensor (if not awarded in (a))

data stored in database/file

compared with

set parameters

previously stored readings [2]

(c) Two from

spreadsheet

graph/chart

database/table [2]

(d) alarm, signal/messages on screen [1]

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(e) Two advantages from

data downloaded periodically/in batches

readings are taken automatically

accurate measurements are made

no human error

readings are taken at exactly the right time

readings are taken continuously/ 24/7

automatic calculations can be made [2]

Q75. A computer is used to control the traffic lights at each end of a narrow bridge.

(a) State one type of sensor that could be used to detect a vehicle approaching

the bridge. [1]

(b) Give one reason why an analogue to digital converter (ADC) may be needed.

[1]

(c) Describe how the data received from the sensors is used to control the timing of

the traffic lights.[3]

(d) If the computer controlling the traffic light system detects an error in the system,

or fails completely, what should the lights on the bridge do? [1]

(e)List use of following sensors:

temperature magnetic field gas pressure moisture humidity pH/acidity/alkalinity motion/ infra-red

(a) Any one from:

pressure

infrared [1]

(b) Any one from:

sensor signal is analogue

computers can only understand digital [1]

(c) Any three points from:

number of cars in both directions are totalled

computer compares this total .. .. with values stored in memory/simulation results changes lights/takes action if necessary

if no data received, default timing is used [3]

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(d) Any one point from:

all lights change to red/amber

lights flash

automatic timing sequence [1]

(e) Temperature Sensor:

A temperature sensor produces a signal that depends on the temperature of its

surroundings.

We can use temperature sensor in many appliance such:

Automatic washing machine

Digital thermometer

Controlling heating system in buildings, including greenhouses and chemical

reaction vessels.

Pressure sensor:

A pressure sensor produces a signal that depends on the pressure to which it is

exposed.

Pressure sensor can be used in many appliances such as automatic blood pressure

monitor. Pressure sensor can also control the pressure of gases or liquids in chemical

reaction vessel.

Magnetic Field:

The Magnetic Field Sensor can be used to study the field around permanent

magnets, coils, and electrical devices

Gas:

A gas sensor produces a signal depending on the concentration of a particular gas

or vapor. We can use gas sensor for an inflammable gas to monitor the atmosphere

and sound an alarm if there is a leakage. We can use gas sensor in other

applications such as:

Breathalyser, which measure the concentration of alcohol vapour in a sample of

breath and estimate the concentration of alcohol in blood.

Process control in chemical industry.

Environment monitoring of air pollution.

Moisture/ Humidity sensor

A moisture sensor produces a signal that depends on the concentration of water

vapors in the atmosphere. A moisture sensor can control an irrigation system more

efficiently only allow water when soil is dry. We can use moisture sensor in many

other application including:

Controlling a heating system and air conditioning system.

Maintaining sufficient humidity in the air in a greenhouse.

Measuring humidity for meteorological record and forecasting in a weather

station.

pH/acidity/alkalinity sensor:

pH Sensor measures the pH of aqueous solutions in industrial and municipal process

applications. It is designed to perform in the harshest of environments, including

applications that poison conventional pH sensors.

Typical activities using our pH sensor include:

Acid-base titrations

Studies of household acids and bases

Monitoring pH change during chemical reactions or in an aquarium as a result of

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photosynthesis

Investigations of acid rain and buffering

Analysis of water quality in streams and lakes

Infrared sensor:

An infra (IR) sensor produces a signal that depends on the level of invisible IR

radiation falling on it.

All objects (unless they are extremely cold) emit significant IR radiation. Security

camera equip with lens and grid of IR sensors uses these IR radiation to form a

detector for a person.

(f) Advantage of using sensors to collect data are:

They can collect data far more frequently than a person.

They are more reliable than a person, who may forget to take readings.

They are more accurate than a person who may misread the signal.

They can collect data from places where it is not possible for a person to go such as

inside a chemical or nuclear reaction vessel.

Disadvantage of using sensors are that they may need a power source to work and

may need regular calibration to check their accuracy.

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Q76. The following flowchart shows how a burglar alarm system uses light sensors to

determine if an intruder has entered the house and decides to sound an alarm.

Select statements from the list below, using numbers only, to complete the flowchart.

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Q77. The following flowchart shows how sensors (which can be analogue or digital) and a

computer are used to control the temperature of a greenhouse for plants.

Complete the flowchart using the items from the list below.

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Q78. The following flowchart shows what happens when a customer uses a credit card to

pay for goods at a supermarket. Ten of the boxes are blank.

Using the items from the list, insert the ten missing statements using the appropriate

number only. Each statement may be used once only.

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Q79. The following flowchart shows how the bar code written on an item is used to find

the price, do stock control and produce an itemised bill. Select statements from the

list below to complete the flowchart.

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Q80. A digital camera contains a microprocessor. The cameras specification includes: 20 megapixel resolution 32 gigabyte memory card autofocus facility (a) A more expensive model of the camera has 40 megapixel resolution.

(i) Describe one advantage of increasing the resolution. [1]

(ii) Describe one disadvantage of having 40 megapixel resolution. [1]

(b) (i) Describe the type of memory used in the memory card. [1]

(ii) Give one benefit of using this type of memory. [1]

(c) (i) What is the meaning of the term pixel? [1]

(ii) If a compressed image file requires an average of 1 byte per pixel, what is the

maximum number of photos that can be stored on the memory card? [1]

(d) Apart from autofocus, describe one other feature you would expect to see on a

digital camera controlled by a microprocessor.

(a) (i) higher quality photos when blown up less likely for photo to pixelate [1] (ii) uses up more memory (on card) takes longer to upload/download a photo file size will be greater [1] (b) (i) solid state memory flash drive non-volatile [1] (ii) no moving parts (so more robust) can be removed from camera and retain its contents can erase contents and reuse memory card [1] (c) (i) (pic)ture (el)ement [1] (ii) 819 or 1638 [1] (d) Any one point from: e.g.

auto flash anti (hand) shake facility easy deletion of unwanted photos ability to manipulate images after they have been taken/special effects smart operation e.g. automatically pick out objects, faces, etc. auto capture [1]

Q81. The workers in the office use three different types of storage medium.

For each of the three types, state a use to which the medium could be put and

justify your answer.

(i) Hard Disk

(ii) DVD-RW

(iii) CD-ROM

(i) Hard Disk

- Files/Software/Operating system

- Need to store large volumes of data/semi-permanently/access to

data/ability to alter contents easily

(ii) DVD-RW

- Back up/Archive

- Need to be portable/to be rewritable

(iii) CD-ROM [6]

- Import software/keep original copies of software

- Cannot be changed (hence lost)/kept in case of need to reinstall [6]

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Q82. State an example of each of the following types of storage medium and give a use

for each.

(i) Magnetic [2]

(ii) Solid state [2]

(iii) Optical [2]

(i) e.g. Hard drive/tape e.g. Storing OS/Software/User files/Back-up (for tape)/transaction file [2] (ii) e.g. Flash Memory/Memory card e.g. Take data from one machine to another/use in camera/mobile phone use as back-up/backing store (iii) e.g CD/DVD/Blu Ray - use as backup/offline storage [2]

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1.3.6 Operating systems

Q83. (a) Define operating system?

Operating system is a software program which controls the operations of the

computer system & manages all of the computers hardware and programs. It acts

as a layer of software between applications programs and hardware and provides

an interface through which a user can run an application. It controls how the

computer responds to users requests and how the hardware communicates with

each other.

(b) Describe the main differences between batch processing and real time

transaction processing. [2]

(b) batch processing

Any one from:

all data (collected together before) processed in one go no human interaction required once processing started system not time sensitive real time transaction processing

Any one from:

requires immediate/quick response updates as data input/received [2]

(c)State three tasks done by the operating system. [3]

Any three points from:

file management resource management = 0

input/output control/peripheral management

spooling

memory management

multitasking/JCL/batch processing

multiprogramming

handling interrupts

error reporting/handling

security

interfaces with users/WIMP type interfaces

loads/runs programs

processor management

manages user accounts

copy/save/format/DOS utilities [3]

Q84. Many household appliances contain embedded microprocessors.

Explain why most of these microprocessors dont need operating systems. [2] (i) Give one example of such a device. [1]

(ii) Give one reason why it does not need an operating system.

(i) any typical device such as a microwave oven [1]

(ii) any one reason from:

has only one set of tasks to perform

simple input expected (e.g. keypad on front of device)

simple, never-changing hardware

would increase development and manufacturing costs [1]

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Q85. Most operating systems provide a user interface.

(a) User interfaces can be either command line interfaces (CLI) or graphical user

interfaces (GUI).

Give ONE advantage and ONE disadvantage of both types of interface.

(a) Any one advantage of CLI from:

direct communication with computer system not restricted to a number of pre-determined options simple interface using keyboard only faster response Any one disadvantage of CLI from:

need to learn a number of/long/complex commands need to type in the commands (possibility of errors) slow having to type in commands every time Any one advantage of GUI from:

only need to click on one simple picture so much easier for the novice several instructions are replaced by one icon no need to understand how computer systems work Any one disadvantage of GUI from:

wasteful of computer memory if user wants to communicate with computer system directly, GUI is effectively more complex. [4]

Q86. Explain, with examples, the following five computer terms:

buffer polling interrupts handshaking checksum.

buffer any two points from:

temporary store/memory

allows speed of CPU/devices to be matched

to hold data being transferred between peripherals and CPU

e.g. pages stored waiting to be printed [2]

polling Method in which operating system periodically checks each peripheral device for

communication is called polling

interrupts any two points from:

a signal/request generated by a device/program power cut = 0

causes a break in execution of a program/stops program

e.g. printer out of paper [2]

handshaking any two from:

exchange of signals/protocols

to establish communication/readiness (to send and receive)

between two devices/computers

examples: printer and computer, modem and computer [2]

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checksum. (v) count of the number of bits before transmission which is sent with the transmission

so that the receiver can check to see whether the same number of bits have arrived

Q87. Give three file management tasks that are done by a computer operating system.

The operating system is responsible for the following activities in connections with file

management:

File creation and deletion. Directory creation and deletion. Support for manipulating files and directories. Mapping files onto secondary storage. File backup on stable (nonvolatile) storage media. Identify and locate a selected file Use a directory to describe the location of all files plus their attributes On a shared system describe user access control Blocking for access to files provide simple and fast algorithms to read and write files give and deny access rights on files to users and programs allocate and de allocate files to processes provide users and programs with simple commands for file handling

Q88. A student gave the following three computer definitions.

Give the name of the term being described in each case.

(i) a signal from a device sent to a computer causing the CPU to stop its current operation temporarily (ii) an exchange of signals between two devices when communicating to ensure synchronisation (iii) a temporary memory to store data waiting to be sent to a device

(i) interrupt

(ii) handshaking

(iii) buffer [3]

Q89. Which five computer terms are being described below?

(ii) signal sent from a printer requesting attention from the processor; this causes a

temporary break in the execution of whatever the processor is doing

(iii) exchange of signals between two devices to ensure synchronisation when

communication starts

(iv) temporary storage area in a printer that holds data waiting to be printed [5]

(v) count of the number of bits before transmission which is sent with the transmission

so that the receiver can check to see whether the same number of bits have arrived

1 mark for each correct term.

(ii) interrupt [1]

(iii) handshaking [1]

(iv) (printer) buffer, RAM [1]

(v) checksum [1]

Q90. State why the process known as handshaking is necessary between a computer

and the file server before use.

To ensure that both are on and ready for communication/to ensure that both are

using same protocol. [1]

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Q91. Describe how buffers and interrupts are used in the transfer of data from primary

memory to secondary storage.

-Data sent to buffer from primary memory

-Processor can continue with other tasks

-Data downloaded from buffer to file server

-When buffer empty, interrupt sent to processor requesting refill of buffer

-Interrupt added to queue and dealt with when top of queue/interrupt dealt with on

receipt by processor.

(1 per -, max 4) [4]

Q92. Describe the stages of the process of transferring data from memory to backing

store. Your answer should include references to buffers and interrupts.

-Processor fills buffer with data

-Processor continues with other job

-Buffer is emptied to storage device

-When buffer empty

-signal sent to processor (interrupt) -requesting further data to be sent to buffer

-dependent on priority

-Processor interrupts present job to refill buffer

-Mention of double buffering

(1 per -, max 6) [6]

Q93. (i) Explain the role of the buffer and interrupts when a large document of over

200pages is sent to a laser printer. [3]

(ii) The use of two buffers would speed up the printing process.

Explain why.

(i) Any three points from:

data is transferred from (primary) memory to printer buffer

when the buffer is full, the processor can carry on with other tasks

printer buffer is emptied to printer

when printer buffer is empty, printer sends an interrupt to the processor

requesting more data to be sent

according to priorities [3]

(ii) Any two points from:

first (block) of data sent to the first buffer

whilst this data is being printed by the printer

next block of data is sent to the second buffer

when the first buffer is empty

data from the second buffer is then printed

meanwhile more data is then sent to the first buffer

this continues until all data has been processed by the printer [2]

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1.3.7 High- and low-level languages and their translators

Q94. Look at these two pieces of code:

(a) Which of these pieces of code is written in a high-level language? [1]

(a) code B [1]

(b) Give two benefit of writing code in a high-level language. [1]

(b) Any one from:

no need to understand workings of a computer easier to understand for programmer/closer to English much easier to debug much easier to test one-to-many when writing commands not machine-specific/portable [1] (c) Give two benefit of writing code in a low-level language. [1]

(c) Any one from:

can address memory addresses directly no need for compilers/interpreters shorter code/code requires less storage/RAM can be written to run faster [1]

(d) High-level languages can be compiled or interpreted.

Give two differences between a compiler and an interpreter. [2]

(d) compiler produces object code / interpreter doesnt produce object code compiler translates whole program in one go / interpreter translates and executes line at a time

compiler produces list of all errors / interpreter produces error message each time an error encountered

compiler produces stand alone code / interpreter doesnt produce stand alone code compilation process is slow but resultant code runs very quickly / interpreted code runs slowly

(e) Give two differences between high level languages and low level languages.

Any two differences from:

high level low level

portable

problem-orientated machine-orientated

close to English can be difficult to read/understand

one-to-many relationship one-to-one relationship

easier to debug/change/upgrade needs assembler

needs compiler/interpreter [2]

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1.5 Ethics

Q95. List ten commandments of computer ethics.

1. Thou shalt not use a computer to harm other people.

2. Thou shalt not interfere with other people's computer work.

3. Thou shalt not snoop around in other people's computer files.

4. Thou shalt not use a computer to steal.

5. Thou shalt not uses a computer to bear false witness (aka Lie).

6. Thou shalt not copy or use proprietary software for which you have not paid.

7. Thou shalt not use other people's computer resources without authorization or

proper compensation.

8. Thou shalt not appropriate other people's intellectual output.

9. Thou shalt think about the social consequences of the program you are writing or

the system you are designing.

10. Thou shalt always use a computer in ways that ensure consideration and respect

for your fellow humans.

Q96. Distinguish between free software, freeware and shareware

Free Software:

Free software means that the users have the freedom to run, copy, distribute, study,

change and improve the software. Thus, free software is a matter of liberty, not

price.

Freeware Software:

Freeware is copyrighted software that is licensed to be copied and distributed

without charges.

Freeware is free because the license says it is, but its still under the owners control.

Example:

Netscape

Internet Explorer

Shareware Software:

The software is licensed for copying and sharing for a trial period, but payment must

be made to the owner for permanent use.

Q97. Explain Lossy and Lossless Compression. Give example of each compression

technique.

Lossless

These are used to make a file a smaller size but without losing any of the

information. Using this method you can always get back to the original file

Example:

PNG

RAW

Lossy

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Sometimes some loss of quality is acceptable. For example the human ear

cannot hear all frequencies, so a file format that throws away parts that people

can't hear may end up with a smaller file, but it is not possible to get back to how

exactly the original music sounded.

Example:

MP3

JPEG

Q98. List the difference between Copyright Vs. Plagiarism

Copyright Plagiarism

One who violets copyright breaks laws

that protect the right of the creator of

an original work.

One who plagiarizes breaks a moral

code by claiming credit for the work of

someone els.

Violation of copyright law may results

in fines, imprisonment or both.

Plagiarism may result in academic

dismissal or loss of job.

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