7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 1/24

 

2.2 Computer Architecture

There is a general introduction, below; the rest of the topic is covered in thefollowing pages:

• Input Devices• Output Devices• Primary and Secondary Memory Devices• Units of Storage and Speed (Kb, MHz etc• !ecent Deve"opments

Each page has a selection of questions so that you can test yourse"f . If you arerevising, try this #uiz on $ard%are&

Introduction

The physical parts of the computer, sometimes said to be "the bits you cankick"  are known collectively as the hardware.

I!"T

#

!$%&E''

#

%"T!"T

(ata )low *odel

The &!" or &entral !rocessing "nit is the "heart"  of the computer and the otherparts +input, output and backing store devices are known as peripherals.

-ack to top

../ 'erial and (irect 0ccess

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 2/24

These are discussed on the page on primary and secondary storage; here is aquick summary qui1 +fill in the missing words by looking back to primary andsecondary storage if necessary.

..23 &omparison of 'erial and (irect 0ccess

 !oints to remember about these methods of file access:

 

Seria"

 

Direct

0 good method if you need to processevery +or nearly every record in a file.Eg payroll processing, electricity bills

4ood if you need to access only a fewrecords in a file and only by one field oreven a record number. Eg bank accountdetails at customers on'"ine request

Tape or disc (isc only

Tape is cheap &ompared to disc

5arder and slower to update files )aster and easier to update files

-ack to top

%r on to:

• Input Devices• Output Devices• Primary and Secondary Memory Devices• Units of Storage and Speed (Kb, MHz etc• !ecent Deve"opments

%r check out:

Historica" Information 0 page that may be of interest; it gives a brief outlineof the different generations of computers from -abbage on up. ot part of t$eI) sy""abus*

..2 Input (evices

The following devices are named in the 'ub6ect 4uide:

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 3/24

• 7eyboard

• *ouse

• Touch 'creen

• %&$

• *I&$

• 'canner +page, mark sense and bar code• 8&( !anels

• 'ound devices

• 9oice rec

• 'ensors

• 'ound sam

• (igital ca

• 4raphics • !rinters

• !lotters

• *onitors

• $obotics

'ome of the most common peripherals will be described in the followingsections but you do not have to restrict yourself to knowing about only these+see -radley $, "nderstanding &omputer 'cience, th edition, I'- 3<=<

3>?, chapters23 and 22, for e@ample.

7eyboard

0 keyboard is really a series of switches each of which generates a series ofdifferent pulse codes so that the computer knows the one that was pressed.They are very useful for typing in te@t, with word processors for e@ample.Ergonomic keyboards provide wrist rests and place the keys at a morecomfortable angle for prolonged use; thus preventing in6uries +such asrepetitive stress in6ury +$'I or carpal tunnel syndrome.

7eyboards, of course, are very useful for entering and editing te@t and theyfeature short cut keys +function keys and numeric keypads to speed upcommon operations.

*ouse

The movement of the mouse generates a series of pulses by which thecomputer can tell the direction of mouse movement. This is often used to movea pointer on a screen, select a menu option or change and create differentwindows in a 4raphical "ser Environment +4"I. The most common e@ample isthe Aindows operating system from *icrosoft or the systems used by 0pple

*acintosh machines. This type of environment is sometimes called a +IMP environment:

 W   Windows 

I  Icons 

 M   Menus (or Mouse) 

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 4/24

  P  Pointers (or pull-down menus)

4raphics Tablet

0 graphics tablet is a kind of flat board on which a pen is moved. The pen holds

a magnet and underneath the tablet is a fine grid of wires. *ovements of thepen cause disturbances in the electrical pulses in the wires and the coordinates of the pen can be detected. It is used, for e@ample, in sophisticatedcomputer art packages and videoediting systems for special effects.

%ne tablet manufacturer in our region is Aacom who market the Intuos rangeof tablets locally. 'ee http:BBap.wacom.co.6pBinde@.html for more info.

8ight !en

Aorks with light, there are two main types. %ne is used to point to areas on

the screen and works by detecting the light emitted by the T9. T9Cs andmonitors work by directing a narrow beam of electrons onto a fluorescentsurface. This beam performs a regular scan, starting at the top lefthandcorner of the screen and traveling down in closely spaced lines until it reachesthe bottom. 0ll of this happens too fast for us to detect but it does mean thatthe beam passes a given spot and a time which can be calculated from aknowledge of the beams speed of travel and the number of +beam not te@tlines on the screen. Thus, this type of light pen can be used to return a positionon the screen. It is mostly used in drawing programs and &0( +&omputer0ided(esign applications.

The other type of light pen, seen in shops, emits a light beam and detects theamount of light reflected. (ark areas reflect less, light areas more. 0 sensordetects the amount of light reflected:

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 5/24

0 typical use of this kind of light pen is to read bar codes, eg in departmentstores and libraries see picture on left. 'upermarkets typically use a "aserscanner which is fi@ed because this speeds up the reading of the barcodes,particularly because many items sold in supermarkets are easily handled and itis then quicker to pass them over a bar code reader than to use a handheld

light pen.

0 library card with a bar code:

%ptical *ark $ecognition +or *ark 'ensing

This uses the techniques described above to detect black marks on whitepaper. 0 common application is in e@aminations where multiple choice papershave several bo@es; candidates mark the bo@ corresponding to the correctanswer +they hopeD usually with a soft pencil. The forms are an e@ample ofpreprinted stationery, some information is already printed on the form +eg,the questions. our I- registration form is a good e@ample of this. The picture

below shows part of the form used in multiple choice e@amination papers+together with some helpful hints on its use.

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 6/24

 

%ptical &haracter $ecognition

The principle of using reflected light is also applied to scanners, fa@ machinesand optical character recognition +%&$. The scanner passes a beam of lightover a page and measures the reflected light. This gives a twodimensionalpattern of light and dark, which can be represented by 2Cs and 3Cs.

Ahen you have the characters or drawings converted to a binary pattern thenyou can send them as a string of electrical pulses to a fa@ machine or importthem into a computer program. Aith %&$, you can try to match the binarypatterns to patterns stored in the computerCs memory and each recogni1edcharacter is then assigned its standard code +0'&II usually.

*agnetic Ink &haracter $ecognition +*I&$

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 7/24

The FfunnylookingF numbers at the bottom of the cheque are encoded inmagnetic ink for use with *I&$ readers at the bank. 'ome banking systemsprefer *I&$ because of the increased reading speed and e@tra security againstforgery compared to %&$. 5owever *I&$ is much more e@pensive than %&$.Ahen the cheque is received by the bank, the amount has to be encoded in the

blank space on the right before the cheque is processed.

0utomatic data entry

The scanning and reading techniques described above can be grouped underthe general heading direct data entry methods. (o not confuse this withautomatic data entry. This occurs when a sensing device is connectedpermanently to a computer and the computer receives data from the sensor atintervals. Sensors are used to collect data when processes are automated, suchas car washes, automatic washing machines, heating control in buildings, petroldelivery in a modern petrol +gas station. These processes may be controlled

with microprocessor applications rather than general purpose computers. Inthis case the program will be stored in $%* and very little $0* will be needed.

(igital cameras

These are becoming increasingly common, with near photographic quality andprices are now comparable to good quality conventional cameras. They can beused with a monitor for applications like video conferencing or simply to takephotographs to display on a web page. "sually some form of data compressionis used when storing and transmitting photographic images to save space anddecrease transmission time. 0 common standard is G!E4 +Goint !hotographic

E@perts 4roup.

9oice recognition

In this technique, the application digitally records speech and attempts tomatch the digiti1ed patterns to the patterns of known words in memory. 'incethere is a wide variety of speech tones, accents and pitches, each individualusing such a system has first to "train"  the application with a set of standardwords. The accuracy is said to be at about /3H for dictation into a wordprocessing document.

Test Yourself with these IB Questions

1.  Three common techniques of direct data entry are MICR, OMR and OCR. For

each of these outline their method of operation and describe a suitable application

[12 marks]

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 8/24

2. tate t!o different de"ices !hich could be used to import ima#es into a !ord

 processin# pac$a#e.

[2 marks]

%.  &escribe the operation of three different input de"ices !hich ma$e use of li#ht.

[6 marks]

-ack to top 

-ack to 0rchitecture !age

%n to %utput (evices !age

 

..2 %utput (evices

9ideo (isplay "nit or *onitor

0 9(" is like a T9 screen but often has higher resolution, the combination of9(" and 7eyboard together is usually referred to as a termina". a typicalmainframe computer will have very many such terminals connected to it. %n apc which is essentially terminal with itCs own microprocessor and $0* the9(" is often known as a monitor. 9("Cs may be monochromatic +single colouror polychromatic. The definition or resolution of a 9(" is a function of the

number of picture elements or pi@els on the screen itself. Each pi@el requires amemory location to store information about itCs state +usually itCs colour.Therefore polychromatic 9("Cs require more memory to store informationabout the state of the screen. 9ery high resolution monitors +4raphical (isplayTerminals or 4("Cs might be used in special applications such as cartography,commercial graphics and design work.

8&(

8iquid &rystal (isplay such as is found on small computers like !alm !ilots andother !(0Cs +!ersonal (igital 0ssistants. -ecause this type of screen doesnCt

perform well in low light conditions, it is often FbacklitF. 5owever, theyconsume very small amounts of power compared to conventional displays andare thus useful in battery operated devices.

for laptop computers passive and active 8&( screens are available, the activetypes having one charge controller +colour element per pi@el giving a brighterand sharper display. %ther advantages +besides low power of these screens

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 9/24

over conventional monitors using crtCs is that they are lighter, flatter, thinnerand give out virtually no radiation.

!rinters

!rinters may be classified in a number of different ways:

  by amount of te@t: character, line or page

  by character formation: matri@ vs nonmatri@;

  by method of printing: impact vs nonimpact;

  by colour colour vs black and white

Dot'matri printers used to be about the cheapest but have now probably beenovertaken in priceBperformance by ink6et printers and are often found on lowvolume systems such as pcCs. They are character, impact and matri@ printers,each character is produced by a set of pins punching an inked ribbon onto the

page. The lowest quality are /pin printers, more pins +pin means higherquality. Typical printing speeds are ?333 characters per second. ou can stillsee them in small businesses used for printing credit card and other receipts.

Daisy %$ee" printers by contrast work like oldfashioned typewriters, eachsolid character, held on the end of a spoke, strikes through an inked ribbononto the paper. The quality is better than that of a dotmatri@ printer but thecharacter set is fi@ed and, as it is a nonmatri@ printer, graphical output is notpossible. This type of printer is becoming rare, good quality is now obtainableby other printers +ink6et, laser at comparable or even lower cost and withoutthe associated noise of the daisy wheel.

0 typical -ineprinter is based on a similar concept but there is a solidcharacter for each position across the page and therefore the printhead doesnot move. 'ince they print 2 whole line at a time they are very much fasterthan character printers.

)or many applications dotmatri@ and daisy wheel printers have beensuperseded by Ink6et and (esktop 8aser printers. In./et printers hold acartridge of ink which is sprayed onto the page in small dots, they are matri@printers. The dots form the characters much like a dotmatri@ printer.5owever, because the ink is liquid it spreads a little on the page and makes a

much smoother appearance. &olour versions are also available and are moreversatile than their dotmatri@ equivalents. -aser printers print a page at atime using a wholepage matri@ of dots, they are very similar to photocopiers inaction. 0 laser beam creates very small dots of static charge on the paper andpowdered toner +ink is attracted to the charged areas. The paper is thenheated and the toner melts onto the page. The quality of these printers is veryhigh and colour laser printers are now available.

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 10/24

!lotters

There are two main types: electrostatic and pen plotters. Electrostatic plotters+available in black and white and colour make an image by burning speciallyprepared paper with a small spark. !enplotters hold a cartidge of several pens

of different colours and actually draw onto the page, giving a higher qualityouput. -oth types are able to plot onto large sheets of paper which can be offi@ed si1e +flatbed plotters or on a large roll of paper +drum plotters.

Touch 'creen

These screens are used both as input and output devices, the options can beshown with te@t and or graphics and the position of a press on the screen canbe detected. These screens are often used where general information is beingprovided +banks, hotels, shopping centres for users who may not be competentcomputer users +yes, there are still some of these.

1.  For each of the follo!in# situations, e'plain your choices of suitable input andoutput de"ices

a( ) tourist information system at an international airport.

[3 marks] 

 b(  )n automated birthday card ma$in# system !hich allo!s input of a name and

messa#e, selection of a card style and suitable #raphics. The card can alsoinclude a photo#raph ta$en at the time of ma$in# the card and the output

required is hi#h*quality colour.

[9 marks] 

c( ) computer*controlled security door.

[3 marks]

+ac$ to top

+ac$ to )rchitecture a#e

+ac$ to Input &e"ices or On to rimary and econdary Memory

.. 'tructure of the &!"

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 11/24

The &entral !rocessing "nit or &!" contains the primary memory of thecomputer and the microprocessor, which has two main units, the &ontrol "nitand the 0rithmetic and 8ogic "nit +&" and 08".

 

.. )unctions of the &!"

(ata is e@changed between these units by the buses. The data bus moves datain both directions +the direction being set by the control bus whereas programinstructions go one way from memory to control unit. The address bus +note@plicitly shown sends address data from the microprocessor to the primarymemory.

The 0rithmetic and 8ogic "nit performs calculations on data and also logicalcomparisons. The &ontrol "nit decodes program instructions and sends

commands to the other units.

.. !rimary and 'econdary *emory

!rimary *emory

The main memory stores the program instructions and the data in binarymachine code. The &ontrol "nit deals with the instructions and the arithmetic

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 12/24

and logic unit handles calculations and comparisons with the data. (ata andinstructions are moved by buses.

 There are two types of memory in the Immediate 0ccess 'tore of thecomputer, $0* and $%*:

$0* is $andom 0ccess *emory which loses its contents when the computer isswitched off +it is volatile. This memory can be written to, instructions anddata can be loaded into it.

$%*, or $ead %nly *emory is nonvolatile and is used to store programspermanently +the startup or FbootF instructions, for e@ample, the computercannot store anything in this type of memory.

Ahen the programs and data files +known as the software are not in $0*, theyare stored on backing store such as tapes or discs. The tape or disc drives and

any input and output devices connected to the &!" are known collectively asperipherals.

&ache *emory

There are two main types of $0*, fast dynamic $0* +($0* or even fasterstatic $0* +'$0*, naturally '$0* is more e@pensive and is thus not used forall of the I0'. 5owever, some '$0* can be placed between main $0* and theprocessor as a temporary store for blocks of program instructions. Ahen theprocessor has to look for the ne@t instruction, chances are it can be found inthe cache. *odern processors also contain a small amount of fast memory

incorporated into the processor itself, internal cache which is speedier stillbecause of the very short distance travelled.

The cache on the microprocessor itself is referred to as 8evel 2 cache and thatbetween main memory and the processor as 8evel .

This site has some useful definitions:http:BBwww.techweb.comBencyclopediaB

whereas the primary memory may be anything from 2> to 2= *bytes for atypical microcomputer +personal computer, the primary memory of a

mainframe or supercomputer may reach 4igabytes in si1e. The cache memoryis typically of the order of a *byte.

)or 5igher 8evel: 8ink to This !age all about registers and the fetche@ecutedecode cycle.

-ack to top

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 13/24

'econdary memory

-acking storage is required to keep information which is not needed in memoryall of the time and which may be too large to fit into the memory of thecomputer. -oth programs and data are held on backing store. The two main

ways of storing data on backing store are seria"'access and direct'access. )ore@ample, a payroll program has to access the data file containing all the dataon all of a companyCs employees, it accesses this data one record at a time,one after the other, this is serial access. (irect access +sometimes calledrandom access would be used, for e@ample, in a supermarket where details ofall of the items for sale are held in a file, the computer needs to locate anitem quickly by moving directly to its record.

*agnetic Tape

This is a serialaccess medium, to read a given record on the tape you must

first pass by all of the preceding records. 0 typical magnetic tape as used intraditional data processing might be 33 feet in length and halfaninch wide.*ore modern versions are tape cartridges which are quite compact +abouttwice the si1e of a cassette tape, typically and store several 4igabytes ofdata. They are often used for backing up large volumes of data. Ahile no newsystems would specify tape drives of the old reeltoreel type, there are stilllegacy systems in use. The data on a tape is stored in parallel tracks:

(0$is "eve" of detai" for H- on"y

-ack to top 

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 14/24

 

0 bit +binary digit J 2 or 3 can be stored in each track, with 2 byte per frameas shown above. The diagram shows a /track tape +other types are possible. 0basic unit of data transfer is the byte which is made up of =bits. Theremaining track +not usually located on the edge of the tape by the way is aparity track. Ahen a byte is written to the tape the number of 2Cs in the byte iscounted, the parity bit is then used to make this number +of 2Cs even +evenparity or odd +odd parity. Then when the tape is read again, the parity bit ischecked to see if an odd bit has been lost somewhere.

 

2 ? > < =

3 2 2 3 2 3 3 2

3 2 2 3 2 3 3 2

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 15/24

2 3 3 3 2 2 2 2

To avoid possible errors, the speed of the

tape drive must be held very steady,however, it does take time for the tape toget up to speed so data is written inblocks separated by interblock gaps seediagram above.

'maller tape units are available for microcomputers and are typically used forbacking up information from fi@ed disc packs. Tape streamers are used inmicrocomputers +pcCs for the same purpose as they are a very efficient way tostore a lot of data. 0 typical tape cartridge used for this purpose can storeseveral 4bytes.

-ack to top 

*agnetic (iscs

'erial access using tapes has itCs disadvantages, particularly if you are in ahurry. If you are running some kind of information system in which speed isimportant you want to be able to locate a given record very much more quicklythan be using serial access on magnetic tapes.

ou can compare serial access and direct access by using a musical analogy, to

find a given song on a tape cassette requires you to wind on through all thoseintervening tracks. %n a &( player however, you can move directly to the pieceyou want to hear.

There are two main types of magnetic disc in general use, the removablefloppy disc and the fi@ed +or hard disc. The fi@ed disc of the pc is the smallercousin of removable disc packs which are found on mainframe and minicomputers. 0 floppy disc stores up to 2.? *bytes or so, a typical pc hard discstores up to 23 4bytes or so +these things change quickly, of course, amainframe disc pack may well store several hundred 4igabytes. 0supercomputer used to model weather patterns over the continental "'0 has asecondary memory of Terabytes. +2 Tbyte J 23 4byte. 0 disc pack +andthe pc hard disc consists of several plates of magnetic material arranged on asingle spindle:

Disc surface termino"ogy (H- On"y

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 16/24

The disc surfaces themselves are divided up into sectors andtracks. 0 typical floppy disc has 23 sectors and =3 tracks. 0 harddisc may have several hundred tracks on each surface +or side.

Disc assemb"ies

In the disc pack, the readBwrite heads are all attached to acommon arm, so that all are reading the same track and sector oneach surface, this is known as a cylinder.

Each part of the disc pack can be referenced by its surface, sector and tracknumber and this combination will be unique for the pack. This part is known asa block.

 

(epending upon the computer operating system in use several blocks may betransferred from disc to Immediate 0ccess 'tore +memory in one go and this isreferred to as bucket si1e. -ecause each block has a unique address, it ispossible to store the addresses of files, and their si1es, in a catalogue on thedisc itself and data +or programs can be retrieved by looking up the address inthe catalogue.

%ptical (iscs

Essentially &( $%*Cs and related technology. The &( $%* in your pc is thesame as those used for playing music but the data is stored in a different

format. The surface of a &( has lands and pits in the surface each of whichcan represent binary states. These very small irregularities are read by areflected laser beam. In practical terms &(Cs are useful for distributinginformation because they are portable and rugged +unlike, say floppy discs andthey store much more data +from around >33 *byte for conventional &( up to.< 4bytes for (9( formats. There are also &($Cs +recordable &(Cs on themarket which you can write to once but read many times +Arite %nce $ead*any J A%$*. 0lso increasingly affordable are the &($ACs which can beused like a large floppy disc. These compete with such magnetic media as KI!discs which typically hold a few hundred *bytes of data.

)or revision, you could print out this summary table and complete it.

-ack to top 

'ome questions on material covered so far.

1.  tate t!o different de"ices !hich could be used to import ima#es into a !ord

 processin# pac$a#e.

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 17/24

[2 marks]

2.  Outline t!o situations in !hich photo#raphic ima#es in compressed form !ould

 be preferred o"er ima#es as bitmaps.

[4 marks

%.  Ma#netic tapes !ith - trac$s can be used to store *bits of data plus a parity

trac$. If the system is usin# e"en parity, complete the follo!in# table/

 

Trac$ 1 2 % 0 3 4i( 5 1 1 1 5 5 5 1 6

4ii( 1 1 1 1 6 5 1 1 1

4iii( 1 1 5 5 5 5 1 5 6

[3 marks]

0.  7'plain, usin# a labeled dia#ram, the concepts of trac$, sector and cylinder !hen

describin# ma#netic fi'ed disc 4hard disc( stora#e.

[6 marks]

.  7'plain the follo!in# terms

 

a( Cache memory.

[4 marks]

 b( C)7.

[3 marks]

c( bus.

[2 marks]

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 18/24

.  tate t!o reasons !hy secondary memory is needed in a computer system.

[2 marks]

3.  It mi#ht be thou#h that, !ith the ad"ent of stora#e de"ices such as !riteable C&8s

and hi#h capacity floppy discs 4systems storin# se"eral hundred me#abytes ofdata( that ma#netic tape is no lon#er needed for secondary memory. Outline t!o

situations in !hich ma#netic tape !ould still be preferred.

[4 marks]

.  &escribe !hat happens to a floppy disc !hen it is formatted.

[6 marks]

..? "nits of 'torage and 'peed

The smallest unit of storage in memory or on disc is the bit +symbol b and thiscan store a 1ero or a one +or equivalent states anyway. The most commonunit is = bits combined into a byte +symbol -:

1 2 2 1 1 2 1 2

The speed of processors describes the number of instructions they can carryout in a second and is measured in cycles per second +or 5ert1 as forfrequency. 0 typical !III processor operates at around ?33 <?3 *51 +cancarry out ?33,333,333 operations per second. )ast.

..>B<B= 'I otation &ompared with &omputer 'torage Terms

'tandard 'I units use prefi@es for si1e such as m for milli +as in mm or

millimetre and k for thousand +as in km or 2333 metres. The prefi@es are:

TTera @2,333,333,333,333

4 4iga @ ,3233,333,333

* *ega @ 2,333,333

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 19/24

k kilo @ 2333

c centi @ 233

m milli L 2B2333

M micro @ 2B2,333,333

nnano @2B2,333,333,333

ppico @2B2,333,333,333,333

*odern computers have masses of memory and disc space to store bytes ofdata and this is therefore measured in larger units as shown below:

k- 0 kilobyte holds 23 bytes

*- 0 megabyte holds 23 kilobytes4- a gigabyte holds 23 megabytes

T- a terabyte holds 23 gigabytes

otice that the storage units are not in 2333Cs but in 23Cs and this is becausecomputer storage is measured in units of 23 +23. 

0 typical pc hard disc of = 4- or so can thus store the equivalent of=,?=/,/,?/ characters, say 2 billion words or ? million pages of data.

-ack to top

-ack to 0rchitecture !age

-ack to %utput (evices or %n to $ecent (evelopments

 

..22 $ecent (evelopments

The architecture in which a single instruction is fetched into the &!" then

decoded and e@ecuted is often called the von eumann architecture after Gohnvon eumann who first described it in a formal paper +see the history page forfurther details and links. This can be restrictive +the von eumannbottleneck since, for e@ample, it is often more efficient to have a single taskperformed by many people.

!rocessor 0rchitecture

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 20/24

Recent de"elopments ha"e included the sin#le and multiple pipeline architectures. In the

sin#le "ersion an instruction can be fetched and another decoded !hile the first is still

e'ecutin#/

fetch decode e@ecute

N instruction

instruction

instruction2

N

In the multiple version pipelines work in parallel to increase the rate ofprocessing of instructions still further. 0 similar idea is to use multipleprocessors in parallel but in both these cases some additional coordination isneeded in case one instruction depends upon the results of another e@ecutingat the same time or later on.

*uch more detail for those interested can be found at, for e@ample, at pagesby Gohn *orris of The "niversity of Aestern 0ustralia. There you will find notes

such as http:BBodin.ee.uwa.edu.auBOmorrisB&03>Bpipelines.html you do notneed this for your studies but you may want to e@plore the topic via ane@tended essay.

'upercomputers and mainframe computers make e@tensive use of multipleprocessors to share the workload. In relatively recent developments such as(eep -lue and the &ray TE supercomputer massively parallel architecture isemployed.

)rom http:BBwww.research.ibm.comBdeepblue

"The latest iteration of the Deep Blue computer is a 32-node IB !#$%%%  &hi'h-performance computer( which utili)es the new &ower Two uper *hip

 processors +&2*, .ach node of the & employs a sin'le microchannel cardcontainin' / dedicated 01I chess processors( for a total of 2$ processorsworkin' in tandem The net result is a scalable( hi'hly parallel system capableof calculatin' $% billion moes within three minutes( which is the timeallotted to each player4s moe in classical chess" 

)rom http:BBwww.cray.comBproductsBsystemsBcrayteBoverview.html 

"The *ray T3.-52%%. T series efficiently scales performance and

 price#performance from tens to thousands of processors and up to 26 trillioncalculations per second +teraflops, The *ray T3.-52%%. distributed-memory

 parallel processin' system follows the successful *ray T3. T system with twicethe performance and four times the memory Breakthrou'h technolo'iesestablish *ray T3.-52%%. as the world4s first 'lobally scalable supercomputerseries

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 21/24

*ustomers include Department of Defense 7aal 8ceano'raphic 8ffice(.lectronic Data ystems +.D,( 9erman !esearch *enter :orschun's)entrum

 ;uelich +<:=,( 7==4s 9oddard pace :li'ht *enter( &hillips &etroleum*ompany( 7ational .ner'y !esearch cientific *omputin' *enter( 7ational8ceano'raphic and =tmospheric =dministration4s 9eophysical :luid Dynamics

1aboratory( ystem .n'ineerin' !esearch Institute in <orea( >nited <in'dometeorolo'ical 8ffice( and the > =rmy ?i'h-&erformance *omputin'*enter"  

Hig$"ig$ts3 

• The industryleading highly scalable supercomputer

• %ffered in configurations from > to ,3= processors; provides fle@ibility

for customer acquisitions• 4lobal scalability allows customers to buy what they need

• *ore than . T)8%!' peak performance, offers the greatest amount of

power for parallel applications• 'upports large parallel workloads with up to T- central memory

• Industryleading bisection bandwidth in e@cess of 24- per second

speeds overall performance on applications• IB% bandwidth of up to 2=4- per second delivers solutions fast

• Easily installed in standard computer facility

 A supercomputer user:

O44567D-Improving weather predictions and environmental research with &raytechnology 

"?i'h-performance supercomputers are critical tools for our research efforts*ray4s systems proide a cost-effectie computin' enironment supported byan e@cellent pro'rammin' enironment The company4s systems were able tosupport our research while proidin' competitie price#performance( a

 predictable 'rowth path( and sufficient archie capacity"  

-ack to top

!rimary memory Technologies

The standard $0* technologies have been '$0* +'tatic $0* and ($0*+dynamic $0*. 5ere is some information taken from the e@cellent site at:

 http:BBwww.hardwarecentral.comBhardwarecentralBtutorials

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 22/24

Memory TypesRAMDavid Risley

Random Access Memory (RAM) is what most of us think of when we hear the word

memory associated with computers. It is volatile memory, meaning all data is lostwhen power is turned off. he RAM is used for temporary storage of program data,allowing performance to !e optimum.

"ike R#M, there are different types of RAM$

• Static RAM (SRAM) his RAM will maintain its data as long as power is

provided to the memory chips. It does not need to !e rewritten periodically.

%RAM is very fast !ut much more e&pensive than DRAM. %RAM is often usedas cache memory due to its speed. 

• Dynamic RAM (DRAM) DRAM, unlike %RAM, must !e continually rewritten in

order for it to maintain its data. his is done !y placing the memory on a

refresh circuit that rewrites the data several hundred times per second. DRAMis used for most system memory !ecause it is cheap and small.

here are several types of DRAM, complicating the memory scene even more$

• Fast Page Mode DRAM (FPM DRAM) 'M DRAM is only slightly faster than

regular DRAM. It uses a slightly more efficient method of calling data from the

memory. 'M DRAM is not used much anymore due to its slow speed, !ut it is

almost universally supported. 

• Extended Data Out DRAM (EDO DRAM) D# memory incorporates yet

another tweak in the method of access. It allows one access to !egin whileanother is !eing completed. *hile this might sound ingenious, the

performance increase over 'M DRAM is only slight. D# DRAM must !eproperly supported !y the chipset, !ut it is the most common type of memoryfor most users. ower users with high !us speeds typically opt for something

faster, though. 

• Burst EDO DRAM (BEDO DRAM) his is !asically D# DRAM with com!ined

pipelining technology. he result is a much faster D# memory chip capa!le

of working with faster !us speeds. %upport for the +D# technology is rathersparse. %DRAM has caught on faster. 

• Synchronous DRAM (SDRAM) %DRAM is the developing new standard for

memory. Its speed is synchronous, meaning that it is directly dependent

on the clock speed of the entire system. It works at the same speed as thesystem !us, up to -M/0. Although %DRAM is faster, the speed difference

isn1t noticed !y many users due to the fact that the system cache masks it.

Also, most users are working on a relatively slow 22M/0 !us speed, whichdoesn1t use the %DRAM to its full capacity. 

• RAMBus DRAM (RDRAM) his is a technology still !eing developed !y Intel

that may prove to surpass %DRAM. Its goal is to get rid of the latency, thetime taken to access memory. It does this !y actually narrowing the !us path

and treating the memory !us as a separate communication channel.

3o see 4 http$55www.hardwarecentral.com5hardwarecentral5tutorials 4 for more on

hardware...

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 23/24

$%*

The point is always made about $%* that it cannot be written to e@cept by aspecial machine +the blower. 0n early development to allow testing ofprograms stored in $%* was the E!$%* or Erasable !rogrammable $%*. These

chips can be recogni1ed by a special window on top of the chip, shining "9light through this window will erase the chips contents and allow it to be reprogrammed.

Aith the very rapid advances in modem and other technologies +scanners, &(Ariters, digital cameras, there was a need for a $%* that could be upgradedin the component itself and these newer devices are fitted with )lash $%* inwhich the program can be changed by downloading suitable software from awebsite.

'econdary 'torage (evices

Ae have mentioned KI! discs and drives and &($A which are relatively newtechniques for storing large +233*- 4- data on portable media. There area number of new storage media for portable devices like *! players anddigital cameras. These include:

• 'mart media

• &ompact )lash

• *emory stick

• *ultimedia &ard

These media contain nonvolatile memory, are typically very small and havelow power consumption. They are ideal for use in small portable electronicdevices which need to store data. Typical si1es range up to > *b on a cardabout twice the si1e of a standard postage stamp.

(ata &ommunications

Increasingly available are two similar types of device. The mobile phone whichhas data acquisition features for web browsing and email reading. Aith the

advent of A0! +Aireless 0pplications !rotocol this technology is e@pected toimprove the amount of data that can be transferred to a mobile phone thusenabling portable web browsing, contact with company intranets and 9!Cs+9irtual !rivate etworks. The !(0 +palm top or personal digital assistantwhich is useful for storing contact information and can be synchroni1ed with apc. !robably these two devices will converge so that you can carry yourschedule and reminders with your telephone and, again, these can be linked toyour companyCs network +and company databases too.

7/27/2019 obje_9.doc

http://slidepdf.com/reader/full/obje9doc 24/24

These kind of technologies are supplemented by ever faster FbackbonesF+systems for transmitting data in networks, including the internet andassociated technologies such as 0T* +asynchronous transmission via cablemodems +about 3 times faster than a ?> k modem.

-ack to top

It is always worth reading about recent developments in technology, theyhappen faster than this web page or books can cover them. Try computermaga1ines and technical websites for items of interest.

:inally( some test Auestions( ust for a chan'eC

1.  The terms serial, sequential and direct access can be used !ith reference to

secondary memory de"ices. Compare these three methods of access.

[6 marks]

2.  &escribe the operation of three different input de"ices !hich ma$e use of li#ht.

[6 marks] 

%.  Outline a situation in !hich a supercomputer !ould be used rather than amainframe.

0.  &efine the term macro and outline a situation in !hich a macro could be used in a

#eneral purpose applications pac$a#e.

[3 marks]

.  &isabled people often ha"e trouble usin# computer systems. &escribe ho! threedifferent input de"ices could be used by people !ith specific disabilities

[9 marks 

.  Compare the operation of a 9:I !ith that of a C;I

[6 marks]

-ack to top

-ack to 0rchitecture !age

%n to &omputer 'ystems