System Unit & Input/ Output Devices & Secondary Storage

8/13/2019 System Unit & Input/ Output Devices & Secondary Storage

1/20

Chapter 4 System Unit & Input/ Output Devices &

Secondary Storage

Objectives:In this chapter we will discuss the following topics:

The major system unit components. How a computer uses binary codes to represent data. Types of memory. Four principal types of bus lines. Four types of ports. Latest Input /Output e!ices Latest "econdary "torage

Learning outcomes:

#t the end of the chapter$ students will be able to:

%. &nderstand and e'plain the major system unit components.

(. )'plain how a computer uses binary codes to represent data.

*. escribe the different types of memory.

+. Identify and describe the four principal types of bus lines.

,. Identify and describe the !arious types of ports.

-. Identify and describe the most common Input /Output e!ices

. &nderstand the importance of "econdary "torage

4 ! Introduction# computer is an electronic de!ice$ operating under the control ofinstructions stored in its own memory$ which can accept data input0$

process the data according to specified rules process0$ produce resultsoutput0$ and store and the results storage0 for future use as shown in Figure

+.1.

1

StorageOutputProcessInput
http://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter4/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter4/competencies.html


2/20

"igure 4 !: 2oncept of 2omputer 3rocessing4enerally$ computer is made of collection of hardware components thatfunction together as a system as shown in Figure +.%. It has si' primarycomponents$ namely input de!ices$ the processor control unit andarithmetic/logic unit0$ memory$ output de!ices$ storage de!ices$ andcommunications de!ices. The processor$ memory$ and storage de!ices arehoused in a bo' case called the system unit.

"igure 4 #: # 2omputer &nit

4 # $he major system unit components

#ll general5purpose computers re6uire the following hardware components:

1. 7emory: )nables a computer to store $ at least temporarily$ data andprograms.

2. "torage de!ice: #llows a computer to permanently retain large amounts

of data. 2ommon storage de!ices include dis8 dri!es and tape dri!es .
http://www.webopedia.com/TERM/C/computer.html#%23http://www.webopedia.com/TERM/C/store.htmlhttp://www.webopedia.com/TERM/C/mass_storage.htmlhttp://www.webopedia.com/TERM/C/disk_drive.htmlhttp://www.webopedia.com/TERM/C/tape_drive.htmlhttp://www.webopedia.com/TERM/C/computer.html#%23http://www.webopedia.com/TERM/C/store.htmlhttp://www.webopedia.com/TERM/C/mass_storage.htmlhttp://www.webopedia.com/TERM/C/disk_drive.htmlhttp://www.webopedia.com/TERM/C/tape_drive.html


3/20

3. Input de!ice: &sually a 8eyboard and mouse $ the input de!ice is the

conduit through which data and instructions enter a computer.

4. Output de!ice: # display screen $ printer $ or other de!ice that lets you

see what the computer has accomplished.

5. 2entral processing unit 23&0: The heart of the computer$ this is the

component that actually e'ecutes instructions.

"igure 4 %: # "ystem unit

#s shown in Figure +.($ "ystem unit is made of the following parts:

7otherboard 5 The motherboard is the main circuit board of a microcomputer.

It is also 8nown as the mainboard or system board.

23& 5 The 23& is the central electronic chip that determines the processing

power of the computer.

7emory 5 7emory is the part of the computer that temporarily stores

applications$ documents$ and stem operating information.

3
http://www.webopedia.com/TERM/C/keyboard.htmlhttp://www.webopedia.com/TERM/C/mouse.htmlhttp://www.webopedia.com/TERM/C/display_screen.htmlhttp://www.webopedia.com/TERM/C/printer.htmlhttp://www.webopedia.com/TERM/C/keyboard.htmlhttp://www.webopedia.com/TERM/C/mouse.htmlhttp://www.webopedia.com/TERM/C/display_screen.htmlhttp://www.webopedia.com/TERM/C/printer.html


4/20

9us 5 # bus is an electronic line that allows %s and 1s to mo!e from one place

to another.

)'pansion "lots 5 )'pansions slots appear on the motherboard. They are

soc8ets into which adapters are connected.

3orts and 2onnectors 5 # port is a connector located on the motherboard or

on a separate adapter.

9ays 5 # bay is a space inside the computer case where a hard dri!e$ floppy

dri!e or 2 5 O7 dri!e sits

3ower "upply 5 # power supply changes normal household electricity into

electricity that a computer can use.

"ound 2omponents 5 # sound card lets a computer play and record high

6uality sound.

Centra 'rocessing Unit (C'U)

Following are the functions of 2&3:


5/20

oes all of the wor8 for the computer

oes all of the mathematics$ mainly addition

oes all the logical comparisons of !alues

irects the flow of data in a computer

2ontrols the operation of the parts of the computer

Today$ all 23&s are microprocessors. # microprocessor is a complete computer on a

silicon chip. It does all of the functions of a computer such as stores data and

instructions waiting to be used$ follows changeable instructions$ does input$

processing$ and output$ 23&s ha!e three basic parts:

a0 The #rithmetic Logic &nit #L&0 5 does all of the mathematics in a computer andall of the logic comparisons of !alues. "ome common logic comparison symbols are:

; e6ual to

< less than

greater than


6/20

7ost computers ha!e a 23& that can do more than +11 7H>. 7H> stands for

megahert>s. # 7H> is %$111$111 cycles per second. 2omputers will soon be

at speeds of o!er a gigahert>$ %$111$111$111 Hert>s.

4 % *o+ a computer uses binary codes to represent data

The computer stores information as a string of >eros 10 and ones %0. The

standard string length is eight 1@s or %@s in a row. This standard length is

called a byte.

# byte e6uals one character

# character is a letter$ number$ or symbol 5 it is about any thing that

can be typed on a 8eyboard

There are (,- standard characters used by almost all computers

In,ormation si-e measurements

Ailobyte A90

o One 8ilobyte e6uals about %1(+ bytes

o %A9 is about %+1 words$ about a half page of typed double5

spaced te't words only0

7egabyte 790

o One megabyte e6uals about %111 A9

o One megabyte e6uals about %$111$111 bytes

o One megabyte e6uals about ,11 pages of te't$ or one large boo8

4igabyte 490

o One gigabyte e6uals about %111 79

o One gigabyte e6uals about %$111$111 A9

o One gigabyte e6uals about %$111$111$111 bytes

o One gigabyte e6uals o!er %$111 boo8s of te't

4 . $ypes o, memory


7/20

3rimary memory can be used directly by the 23&. 3rimary memory is also called

primary storage. It consists of silicon chipsB usually either CL" or CL"I technology is

used to create the chips. Two forms of 3rimary 7emory are:

ead Only 7emory O70

andom #ccess 7emory #70

ead Only 7emory O70

"tores instructions that are used by the 23&

Tells the 23& how to be the 8ind of computer it is$ for e'ample a

Dindows$ 7acintosh$ or 3lay "tation computers.

Tells the 23& how to wor8 with the different parts of the computer

O7 can also hold programs that are directly accessed by the 23&.

One such program is the self5test when the computer is first turned on.

The self5test tests to seem if all the parts on the main circuit board

mother board0 are wor8ing correctly.

The instructions in O7 can not usually be changed

The instructions are built into the electronic circuits of the chips

These instructions in O7 are called firmware

To change the instructions in O7 you need to usually change the

chips or do some other special process that is normally not a!ailable to

an a!erage user.

The instructions in O7 are non!olatile. They stay in O7 e!en when

the computer is turned off.

andom #ccess 7emory #70

7


8/20

#ccess to information is random access.

andom access means that any piece of information in O7 can be

accessed at any gi!en time without access other information first. It is

a lot li8e the trac8s on a music 2 . Eou can access any trac8 at any

time and in any order.

The other 8ind of access is se6uential access. Eou must access the

information in the order that they are located. This is a lot li8e a music

tape. Eou must play the songs in order$ or you ha!e to fast forwardpast songs to get to the one you want.

"tore data and instructions that are used by the 23& to perform some

tas8.

These instructions are usually loaded into #7 from a secondary

storage de!ice.

#7 is also used to store instructions that tell the 23& how to wor8

with its parts. These instructions are usually called dri!ers. The instructions in #7 are constantly changing$ depending on the

needs of the 23&.

The instructions in #7 are !olatile.

Dhen the computer is turned off the information in #7 disappears.

The information in #7 needs to be sa!ed to secondary storage before

the computer is turned off.

#ccess to information is random access.

egisters 5 &sed to store data and instructions inside the processor and si>e

of the registers can affect the speed and performance of the processor.


9/20

2ache memory

2ache pronounced cash 0 memory is e'tremely fast memory that is built into

a computer s central processing unit 23&0$ or located ne't to it on a

separate chip. The 23& uses cache memory to store instructions that are

repeatedly re6uired to run programs$ impro!ing o!erall system speed. The

ad!antage of cache memory is that the 23& does not ha!e to use the

motherboard s system bus for data transfer. Dhene!er data must be passed

through the system bus$ the data transfer speed slows to the motherboard s

capability. The 23& can process data much faster by a!oiding the bottlenec8

created by the system bus. 2ache that is built into the 23& is faster than

separate cache$ running at the speed of the microprocessor itself. Howe!er$

separate cache is still roughly twice as fast as andom #ccess 7emory

#70. 2ache is more e'pensi!e than #7$ but it is well worth getting a 23&

and motherboard with built5in cache in order to ma'imi>e system

4 4 "our principa types o, bus ines

# bus is a communication pathway connecting two or more de!ices. # 8ey

characteristic of a bus is that it is a shared transmission medium. 7ultiple

de!ices connect to the bus$ and a signal transmitted by any one de!ice isa!ailable for the same time period$ their signals will o!erlap and become

garbled. Thus$ only one de!ice at a time can successfully transmit. In many

cases$ a bus actually consists of multiple communication pathways$ or lines.

)ach line is capable of transmitting signals representing binary % and

binary1. O!er time$ a se6uence of binary digits can be transmitted across a

single line. Ta8en together$ se!eral lines of a bus can be used to transmit

binary digits simultaneously in parallel0. For e'ample$ an G5bit unit of datacan be transmitted o!er eight bus lines. 2omputer systems contain a number

of different buses that pro!ide pathways between components at !arious

le!els of the computer system hierarchy. # bus that connects major

computer components 23&$ memory$ I/O0 is called a system bus. The more

9


10/20

common computer interconnection structures are based on the use of one

more system buses.

us Structure

# system bus consists$ typically$ of form ,1 to %11 separate lines. )ach line is

assigned a particular meaning or function. #lthough there are many different

bus designs$ on any bus the lines can be classified into three functional

groups: data$ address$ and control lines. In addition$ there may be power

distribution lines that supply power to the attached modules. The data lines

pro!ide a path for mo!ing data between system modules. These lines

collecti!ely are called the data bus. The data bus typically consists of G$%-$

or *( separate lines$ the number of lines being referred to as the width of the

data bus. "ince each line can carry only % bit at a time$ the number of lines

determines how many bits can be transferred at a time. The width of the

data bus is a 8ey factor in determining o!erall system performance. For

e'ample$ if the data bus is G bits wide$ and each instruction is %- bits long$

then the 23& must access the memory module twice during each instruction

cycle. The address lines are used to designate the source of destination of

the data on the data bus. For e'ample$ if the 23& wishes to read a wordG$%-$ or *( bits0 of data from memory$ it puts the address of the desired

word on the address lines. 2learly$ the width of the address bus determines

the ma'imum possible memory capacity of the system. Furthermore$ the

address lines are generally also used to address I/O ports. Typically$ the

higher order bits are used to select a particular module on the bus$ and the

lower order bits select a memory location or I/O port within the module. For

e'ample$ on an G5bit bus$ address 1%%%%%%% and below might reference

locations in a memory module module 10 with %(G words of memory$ and

address %1111111 and abo!e refer to de!ices attached to an

I/O module module %.0


11/20

The control lines are used to control the access to and the use of the data

and address lines. "ince the data and address lines are shared by all

components$ there must be a means of controlling their use. 2ontrol signals

transmit both command and timing information between system modules.

Timing signals indicate the !alidity of data and address information.

2ommand signals specify operations to be performed. Typical control lines

include.

0emory 1rite: 2auses data on the bus to be written into the addressed

location.

0emory 2ead: 2auses data from the addressed location to be placed on

the bus.

I/O 1rite: 2auses data on the bus to be output to the addressed I/O port

I/O 2ead: 2auses data from the addressed I/O port to placed on the bus.

$rans,er 3C : Indicates that data ha!e been accepted from or placed on

the bus.

us 2e5uest: Indicates that a module needs to gain control of the bus.

us 6rant: Indicates that a re6uesting module has been granted control of

the bus.

Interrupt 2e5uest: Indicates that an interrupt is pending.Interrupt 3C : #c8nowledge that the pending interrupt has been

recogni>ed.

C oc7: &sed to synchroni>e operations.

2eset: Initiali>es all modules

The operation of the bus is as described in Figure +.+. If one module wishes

to send data to another$ it must do two things:

%. Obtain the use of the bus$ and

(. Transfer data !ia the bus.

If one module wishes to re6uest data from another module$ it must do two

things:

11


12/20

%. Obtain the use of the bus$ and

(. Transfer a re6uest to the other module o!er the appropriate control and

address lines.

It must then wait for that second module to send the data.

"igure 4 4: Instruction cycle state diagram

4 8 "our types o, ports

There are lots of external devices that you can connect to your computer. #lle'ternal de!ices connect to the computer s system unit !ia cables and ports

where a JportJ is the slot into which you plug a cable0. &nless you re using a

portable computer$ you probably ha!e se!eral e'ternal de!ices attached to

your computer already$ including a mouse$ 8eyboard$ monitor$ microphone$

and spea8ers$ as in Figure +.%. Dhate!er e'ternal de!ices you ha!e$ they@re

all connected to the system unit where the actual JcomputingJ ta8es place0

!ia cables. )ach cable plugs into a specific port on the system unit. The ports

are usually on the bac8 of the system unit. 9ut they can be on front or side

as well. )!erything has a name$ e!en belie!e it or not0 those little plugs on

the bac8 of your computer. Figure +., shows e'amples of some ports. 9ut

your computer@s ports won@t necessarily be the same.


13/20

&"9 and FireDire 3orts

Of all the ports on a computer$ &"9 and I))) %*K+ a.8.a. FireDire0 get all the

hype. There are se!eral reasons for this: 9oth are new technologies$ both

pro!ide Jhot5pluggableJ connecti!ity$ both pro!ide !ery high5speed data

transfers. The hot5pluggable part means you can just plug in some de!ice$

li8e a digital camera or !ideo camera$ and start using it right away. The

older ports would all re6uire you to shut down the computer$ plug in the

de!ice$ restart the computer$ and then install the de!ice.0. In short$ both &"9

and FireDire are a lot more con!enient than the older ports that preceded

them. "o what are the differences In a nutshell$ &"9 &ni!ersal "erial 9us0

was created as a general5purpose high5speed connection to the computer. Its

high speed ma8es it ideal for connecting digital cameras to the computer.

9ut it@s good for lots of other de!ices too$ li8e a Deb cam$ broadband

modem$ whate!er.

13


14/20

"igure 4 8: )'amples of ports

I))) Institute of )lectrical and )lectronics )ngineers0 %*K+$ also 8nown

commercially as FireDire$ is a faster connection than &"9$ but not as widely

used. In consumer electronics$ it@s mostly digital !ideo cameras that connect

through a FireDire port. There are also some high5speed e'ternal dis8 dri!es

and networ8ing components that can use that port. 9ecause FireDire de!ices

are relati!ely rare$ FireDire ports are also rare. Must about any computer you

buy will ha!e at least two &"9 ports. 9ut it@s unli8ely you@d get a FireDire

port if you didn@t specifically order it with your 32. Of course$ you can always

add a FireDire port at any time. ?o problem there0.


15/20

#s though to confuse matters e!en more$ the plugs for &"9 and FireDire loo8

!ery much ali8e. )ach port type$ howe!er$ has its own little logo$ as shown in

Figure +.,.%. #s you can see just by loo8ing at the plugs$ the plug for &"9 will

not go into a FireDire port$ or !ice5!ersa.

"igure 4 8 #: &"9 and FireDire ports computer side of cable0

?ote that Figure +.,.% shows how &"9 and FireDire ports as they loo8 on a

computer. On the de!ice you@re connecting for e'ample0$ the plug might be

an entirely different si>e and shape. 2hec8 the manual that came with your

de!ice if you can@t find the right plug.

4 9 Latest Input /Output DevicesDireless es8top 7ouse

The latest wireless des8top mouse is claimed to be (1 times more sensiti!e

than a typical optical mice$ for greater accuracy and impro!ed use on shiny

surfaces ideal for gamers$ graphic design or those who simply demand

ma'imum accuracy. It is rechargeable !ia the &"9 charge cable. Direless

technology pro!ides a clean$ uncluttered wor8space free from cables. De can

just plug the wireless recei!er and charge cable into the e'tension port$ andthere is no need to reach around your 32. It can scroll5up$ scroll5down$ #lt5Tab

application window switch0 and Internet na!igation Nforward and Nbac8

buttons pro!ide simple and producti!e short cuts for Dindows use. Figure

+.-.% shows a wireless mouse.

15


16/20

"igure 4 9 #: # Direless 7ouse

Direless Aeyboard

# wireless 8eyboard can do more anytime$ anywhere. It wor8s with many

popular 3 #s$ 3 #/2ellular and "mart 3hones. It is full5si>e$ wireless infrared

I 0 8eyboard5 Folds out in seconds$ adjusts to ideal !iewing angle$ and then

folds to fit in your poc8et or purse. It feels li8e a standard 8eyboard. "ee

Figure +.-.(

"igure 4 9 %: # Direless Aeyboard

igital "canner: # digital scanner has become a !ery popular input de!ice for

a 32. Dhen a scanner is attached to the computer$ the scanner can read

information of color or blac8 and white picture. The scanner sends

information to the computer$ which we place on the glass surface of the

scanner. The computer can store this information fore!er$ or can send it

across the world by using Internet in few minutes.

7icrophone: 9y using microphone$ we can record our !oice in a computer.

This de!ice is !ery easy to use and we can record our !oice with music in the

computer through this de!ice.


17/20

igital 2amera: igital camera is used to draw photos. 9y using this input

de!ice images or photos are sent directly to 32 instead of storing on a usual

camera film.

4 Latest Secondary Storage

"econdary storage$ being non!olatile$ retains data e!en when the computer

is turned off. "econdary storage is the nearest thing to permanent storage$

but it will e!entually wear out or be discarded due to outdated technology. It

is also infinite. Dhen one storage de!ice runs out of space$ you can replace it

with another$ which differs from #7$ which has a finite si>e.

# !ariety of secondary storage de!ices are a!ailable$ and they include floppy

dis8ettes$ tape storage systems$ magnetic dis8 dri!e systems$ optical data

storage products$ and remo!able cartridge hard dri!es. # well58nown

manufacturer of secondary storage de!ices is Iomega$ which produces the

popular Pip dri!e. #nother Iomega secondary storage de!ice$ the Ma> dri!e$ is

no longer being produced$ although Iomega continues to offer Ma> %49 and

(49 dis8s and accessories. For large storage needs$ Iomega offers 3eerless$

a remo!able storage product that can hold %149 and (149 dis8s. Theseproducts pro!ide high5capacity data storage: Pip dis8s hold (,179 and Ma>

dis8s hold as much as (49. #nother secondary storage manufacturer is

"torageTe8$ which produces dri!es and cartridges for secondary storage.

One of the more popular secondary storage de!ices is the optical disc. Dith

optical discs$ a laser beam reads and writes data to a disc. Optical discs do

not spin and they do not need to mo!e read/write heads or access arms

because the laser beam mo!es electronically. The capacity of optical disc

storage is far greater than other types of storage de!ices. The most

fre6uently used type of this secondary storage de!ice is a 2 5 O7.

17
http://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.htmlhttp://highered.mcgraw-hill.com/sites/0072464194/student_view0/chapter6/competencies.html


18/20

#nother e'ample of secondary storage is a magnetic tape. The tape is

coated with magnetic material on which data is stored. 7agnetic tapes are

usually used for bac8up purposes. They are slower than a hard dri!e$ but

they are an ine'pensi!e solution for data storage. ata is encoded from your

computer onto a magnetically coated strip of plastic tape0. Tape dri!es are

slower because tapes are a se6uential5access media. This means that to get

to any specific point on the tape$ the dri!e must go through all of the

preceding pointsB this is why tapes are only used for long5term storage.

"econdary storage de!ices pro!ide two types of data access: se6uential or

direct. Dith se6uential storage$ the computer searches for and retrie!es data

in the same order it was stored. 7agnetic tapes are e'amples of a se6uential

secondary storage de!ice because they store date se6uentially. irect5access

storage de!ices$ which are also called random access$ go directly to the

storage location for the re6uested data without reading through other data in

se6uence.

Summary:# computer is an electronic de!ice$ operating under the control of

instructions stored in its own memory$ which can accept data input0$

process the data according to specified rules process0$ produce results

output0$ and store and the results storage0 for future use . #ll general5

purpose computers re6uire the following hardware components: memory ,

storage de!ice$ input de!ice , output de!ice , and the central processing unit

23&0. The computer stores information as a string of >eros 10 and ones %0.

There are four types of memory: primary memory$ ead Only 7emory

O7 0$ andom #ccess 7emory #70$ egisters and 2ache memory.

3rimary memory is also called primary storage$ consists of silicon chips and

can be used directly by the 23&.
http://www.webopedia.com/TERM/C/memory.htmlhttp://www.webopedia.com/TERM/C/mass_storage.htmlhttp://www.webopedia.com/TERM/C/device.htmlhttp://www.webopedia.com/TERM/C/input_device.htmlhttp://www.webopedia.com/TERM/C/output_device.htmlhttp://www.webopedia.com/TERM/C/output_device.htmlhttp://www.webopedia.com/TERM/C/CPU.htmlhttp://www.webopedia.com/TERM/C/memory.htmlhttp://www.webopedia.com/TERM/C/mass_storage.htmlhttp://www.webopedia.com/TERM/C/device.htmlhttp://www.webopedia.com/TERM/C/input_device.htmlhttp://www.webopedia.com/TERM/C/output_device.htmlhttp://www.webopedia.com/TERM/C/CPU.html


19/20

# bus is a communication pathway connecting two or more de!ices. #ll

e'ternal de!ices connect to the computer s system unit !ia cables and ports .

Latest Input /Output e!ices include the Direless es8top 7ouse$ Direless

Aeyboard$ igital "canner$ 7icrophone and the igital 2amera . "econdary

"torage includes floppy dis8ettes$ tape storage systems$ magnetic dis8 dri!e

systems$ optical data storage products$ and remo!able cartridge hard dri!es.

;


20/20

*. &"9 &ni!ersal "erial 9us0

+. ports.

,. control lines

-. data bus

. cache memory

G. #7

K. O7

%1. gigabyte

Documents

System Unit & Input/ Output Devices & Secondary Storage