Hardware…and the stupidity of a computer

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Hardware and software

• In order to make a computer do something useful, we need both hardware and software

• Hardware: The physical parts of the computer (monitor, keyboard, mouse and whatever is ”inside the box”)

• Software: The computer programs (Word, Messenger, Counterstrike, Internet Explorer,…) we use for solving various tasks using the computer

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The computer way

• In order to understand hardware, you need to know a little about how a computer ”thinks”

• A computer does not ”think”, it calculates!

• How can you make pieces of metal calculate anything useful…?

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On or Off

• A computer calculates using metal and current

• A computer can only ”sense” if a current is ”On” or ”Off”

• How can we employ this for doing calculations?

• A transistor is used for this exact purpose

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Transistor

• A transistor is a very simple electronic device

• Two wires lead into the transistor, one wire leads out

• The smart part: The transistor can perform a (sort of) calculation, based on whether or not there is a current in the two input wires

• A so-called logical function

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A smart (?) transistor

• So, what calculation is that?• Not so impressive, actually

A B YOff Off On

Off On On

On Off On

On On OffInput

Output

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Logical, right…?

• The calculation performed by the transistor is an example of a logical function

• A logical funtion takes one or more input values, and pro-duces a single output value

• BUT these values can only be either true or false

• Also know as Boolean logic

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Logical functions - example

A B Y

false false

false true

true false

true true

Two input values

Four possible combinations

Output

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Logical functions - exampleA B C Y

false false false

false true false

true false false

true true false

false false true

false true true

true false true

true true true

Three input values

Eight possiblecombinations

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Logical functions - transistor

A B Y

false false true

false true true

true false true

true true false

If we putOff = falseOn = true

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Zeroes and Ones

• If we now exchange true with 1 (one), and false with 0 (zero), the previous table becomes:

A B Y

0 0 1

0 1 1

1 0 1

1 1 0

• This is how we usually denote ”On” and ”Off”

• A numeral system using only 0 and 1 is also known as a binary numeral system

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The binary numeral system

• Computers use the binary numeral system (aka base-2), humans (mostly) use the decimal numeral system (aka base-10)

• In the context of a base-10 system, 110 means: 1x100 + 1x10 + 0x1 = 110

• In the context of a base-2 system, 110 means: 1x4 + 1x2 + 0x1 = 6

• Alternatively:– 11010 = 1x102 + 1x101 + 0x100 = 110– 1102 = 1x22 + 1x21 + 0x20 = 6

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The binary numeral system• Even if binary numbers appear a bit strange, the

rules for calculation are the same as for base-10– In base-10: 5 + 7 = 12– In base-2: 101 + 111 = 1100

• Using a carry works just as before:0 + 0 = 0

0 + 1 = 1

1 + 0 = 1

1 + 1 = 0, and 1 to carry

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Transistors revisited

• The transistor we saw before was not able to do correct binary addition

• However, if you are clever enough, you can combine transistors to implement other logical functions

• Proper binary addition is just a special logical function

1+1 = ?

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Transistors revisited

• The original transistor worked like this:

A B Y0 0 1

0 1 1

1 0 1

1 1 0

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Transistors revisited

• If you combine two transistors, you can implement a different logical function

A B Y0 0 1

0 1 0

1 0 1

1 1 1

A

B

Y

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Transistors revisited

• The combination before was not very useful, but we can of course just build more complex combinations, involving more transistors

• Our goals is to be able to do binary addition • Binary addition is ”just” a special logical function,

taking three input values and producing two output values

• Can be considered to be two separate logical functions

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Binary additionA B Carry

inY Carry

out

0 0 0 0 0

0 1 0 1 0

1 0 0 1 0

1 1 0 0 1

0 0 1 1 0

0 1 1 0 1

1 0 1 0 1

1 1 1 1 1

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This should do the trick…

• Some clever person found out that the below combination implements proper binary addition

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The first building block

• We have now found a way to do proper addition, using metal and current

• Implementing the other arithmetic operations is then not particularly complicated

• This actually forms the foundation for the first electronic computers

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ENIAC

• Built around 1945• Weighs about 30 tons• Based on vacuum tubes• Ca. 18.000 transistors• Used for calculating

projectile trajectories• Was only operational

about half of the time…

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60 years later

• Today we do not use individual transistors. A chip contains a (large) number of transistors

• Most advanced chips contain a few billion transistors – within an area of perhaps 1 cm2

• What if car technology had progressed at the same rate:– Price: 1 $– Gas consumption: 10.000 km/l– Max speed: 100.000 km/h

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Moore’s law

• ”Within two years, the number of transistors on a chip will double”

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From 0 and 1 to Counterstrike

• Even if we can now make metal and current do calcu-lations, there is still a very long way from 0’s and 1’s to Counterstrike…

• A computer can handle vast amounts of data, at vast speeds– How fast?– How much data?

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Bits and bytes

• For a computer, the basic unit for data is an entity which is either 0 or 1

• This entity is called a bit• A computer performs operations on bits.• A more practical unit is a sequence of 8

bits; this is known as a byte.• Why 8 bits? Why not 7 or 9? Tradition…• We can for instance define a character set

using 8 bits

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Bits and bytes• How many distinct bytes are there?• One byte is 8 bits, each bit is either 0 or 1• Combinations: 2x2x2x2x2x2x2x2 = 256 (28)• Each combination can now be interpreted as a

specific symbol (letter, number, etc), for instance the letter ”H”

• With 256 combinations, we have enough combinations for capital letters, small letters, numbers, etc..

• Example: ASCII codes

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ACSII codes

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Amounts of data

• Amounts of data are usually measured in bytes (each byte being 8 bits)

• For a computer, all kinds of data are just sequences of bits

• It requires a program – written by humans – to interpret a bit sequence as e.g. music, video, a Word docu-ment, and so on

• How many bytes does each type of data require?

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Size of some data types

Plain text

(no pictures)

Music

(mp3 format)

Video

(DVD quality)

Kilo-byte Half a page --- --

Mega-byte 500-page novel

One minute One second

Giga-byte Large book-shelf

16 hours 20 minutes

Tera-byte Large library Two years Two weeks

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Speed of calculation

• When a computer calculates, it processes many sequences of bits simultaneously

• All calculation units must be ”syn-cronized” for this to work properly

• A ”conductor” manages when the calculation units should calculate

• The speed of the conductor defines the speed of the computer

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Speed of calculation

• How many ”beats per second” (hertz) can the conductor manage?

• Old computer (ENIAC); about 10.000 beats per second (10 kiloHertz)

• Modern PC; about 3.000.000.000 beats per second (3 GigaHertz)

• Also known as clock rate

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3.000.000.000 Hertz

• Three billion beats per second is quite fast…

• For every beat, light only travels 10 centimeters

• The physical size of the chip begins to matter

• Unfortunately, energy consump-tion rises with the clock rate, at a quadratic rate

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CPU

• Where are calculations actually performed?• Calculations are done in a unit called the CPU

(Central Processing Unit)• This unit is basically just one large chip, which

looks fairly uninteresting…

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The CPU and Primary Storage

• The job of the CPU is to perform calculations on streams of bits, but who provides these bits?

• Somebody has to feed bits to the CPU, and ”consume” the results produced by the CPU

• For this task, the computer uses the Primary Storage

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Primary Storage• A calculation involves the below steps

– Input data is moved from primary storage to the CPU– The CPU performs the calculation– The result is moved from the CPU to primary storage

• The primary storage is thus just a ”container” for a certain amount of data

• The primary storage is ”passive”; no kind of data processing is performed here

• Primary storage is usually of the type RAM (Random Access Memory)

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Primary Storage

• What is primary storage physically?• Just some chips, which contains a

certain amount of data• A modern PC will typically have 2-8

Gigabytes of primary storage• What could the data represent? For

instance data from an mp3-file, for which the CPU must perform some calculation to transform it into music

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Primary vs. Secondary

• Primary storage (RAM) has a large advantage: transfer of data between the CPU and RAM is quite fast (several Gigabytes pr. second)

• Fast – but compared to what?• There are however also several drawbacks:

– RAM is expensive (compared to what?)– When power is cut, all data in the primary storage will

be lost

• We thus also need secondary storage

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Secondary storage

• Who provides data to the primary storage? That data is provided by secondary storage

• What is secondary storage? In principle the same as primary storage – a passive container for data - but– Is much cheaper than RAM (per byte)– Data is preserved when power is turned off

• Presently, the most common form of secondary storage in a PC is a hard drive

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Quite hard…(old school)

• A (traditional) hard drive con-tains a number of magnetic platters, on which individual bits are stored by magnetising a specific area of the platter

• A modern hard drive contains 500-2,000 Giga-bytes of data

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Quite hard…(new school)

• A SSD (Solid-State Drive) hard drive contains a number of memory chips, on which individual bits are stored in transistors (but retained when power is turned off)

• A modern SSD contains 60-500 Giga-bytes of data

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Hard drive vs. RAM

Hard drive

(Traditional)

Hard drive

(SSD)

RAM

Typical amount in PC

500-2000 GB 60-500 GB 2-8 GB

Price pr. Gigabyte

≈ 0,5 kr. ≈ 10 kr. ≈ 100 kr.

Data transfer speed

0,1-0,3 GB/sek 0,5-1 GB/sek 4-8 GB/sek

Preserves data without power

Yes Yes No

Technology Mechanical Electronic Electronic

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Harddisk vs. RAM

• In other words:• RAM:

– Very fast and stable, BUT– Expensive, does not preserve data

without power

• Hard drive:– Cheap, large capacity and preser-

ves data without power, BUT– Rather slow, mechanical technology

(except SSD)

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Other types of secondary storage

USB-key CD, DVD and Blu-ray

Floppy disks Online

Capacity

(Gigabytes)

2-256 0,7-30 0,0015 (!) ??

Price

(kr pr. GB)

Ca. 10 Ca. 1 >100 ??

Speed

(MB pr. sek)

10-100 25 < 1 Depends on connection

Technology Electronic Optical / Mechanical

Magnetic / Mechanical

Internet

Note Same tech as SSD

Stagnant Almost extinct

On the rise

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Motherboard

• A PC contains a board, on which the central components of the PC are mounted – this board is usually denoted the motherboard

• The motherboard will (at least) contain– CPU– RAM (primary storage)– Auxiliary components– Sockets/slots for adding ”other components”

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Other components

• Examples of ”other components” are:– Graphics card– Sound card– Network card– TV card

• In some PCs, these components are found directly on the motherboard, on others they are found as extra components, inserted into slots on the motherboard

• Why…?

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Other components

• Even though a modern CPU is very fast, it may benefit from being relieved from certain tasks

• Graphics card– Specially designed for effective

graphics calculations– Takes computational load off CPU– May increase graphical performance

by a factor 100– Typical application: GAMES!

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Data exchange by bus

• All these units and components need to exchange data in order to do their job

• How do they do that?• Data exchange is done using

so-called data buses• A data bus transports data

between two units

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Data exchange by bus

• A data bus sends data:– A number of times pr. second– A certain amount of data each time

• Example: a 32-bit bus running at 100 Mhz– Carries 32 bit (4 bytes) each time– Sends 100 million times pr. second

• A PC contains a number of buses running at different speeds

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Countryside bus

• A bus is also used for exchanging data with additional components, like a graphics card

• Types of buses for extra components:– PCI (Peripheral Component Interconnect) – those

slots in which additional components (such as a graphics card) can be inserted

– USB (Universal Serial Bus) – used by many external devices such as printers, USB memory keys, etc..

• Fortunately, buses follow a standard

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External devices

• Devices which enable communication between humans and computers

• Typical external devices– Keyboard and mouse– Monitor– Speakers / headset– Printer

• But also– Digital camera, phone, USB-key, …