cse1010e chapter 2

8/7/2019 Cse1010e Chapter 2

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CHAPTER 2

STEPPING IN THE COMPUTER

Learning Objectives

Upon completion of this unit, you should be able to do the following:

1. Identify the different components of a computer.

2. Understand how these different components work individually and howthey integrate with each other.

3. Choose the appropriate components for a PC.

4. Understand how to build a computer.

OverviewWhat is a computer? It is a device that processes data and converts it tomeaningful information. So, it needs to acquire the data, process it and thenoutput information which means it needs input devices, output devices anda processing unit (and backing storage devices to store additionalinformation).

To process that data, there needs to be a sort of brain that can analyseinformation; this brain is found inside the system unit which contains manypieces of electronics among which the most important are arguably theprocessor, motherboard, memory and graphics card.

2.0 IntroductionEveryone has seen a computer but how many people have opened one andknow how it works? Very few. In this chapter, we will attempt to understandhow a computer works and we will also see the basics of assembling acomputer.

2.1 Main Components of a ComputerA computer is a device that accepts inputs and transforms them intooutputs. The input is raw, unprocessed data that we feed into thecomputer and the output is the processed information that results.A computer system can be represented as follows:


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Figure 2-1 Simple block diagram of a Computer System

As can be seen in Figure 2-1, a computer is made up of four components:

Input Process Output Backing Storage

2.1.1 Input and OutputInput devices are used to enter data into a computer. The most commonexamples are the mouse and the keyboard.Output devices are used to display the data processed by the computer. Themost common output devices are the monitor and the printer.

2.1.2 Backing StorageBacking storage devices are used to store data processed by the computer.For example, a bank stores data and information about its customers (name,bank account number, address,...) on a backing storage device. Commonbacking storage devices include hard disks, CDs and DVDs.

2.2 System UnitThe System Unit is the core part of the computer. It contains the componentsthat will process the data entered through input devices and will outputmeaningful information. The System Unit is contained inside a casing asshown in Figure 2-2.


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Figure 2-2 Computer inside view

Does all this mess appear scary? To the uninitiated yes, but the apparentlychaotic world is precisely ordered as we will see in the next sub-sections.

2.2.1 ProcessorThe processor is the brain of the computer; it processes data and converts itinto meaningful information. Arguably it is the most important component ofthe computer. It is jam packed with electronic components called transistorsand it operates at very high speeds. The speed of the processor will normallydetermine how fast data is processed by the computer a 3 Ghz processormeans that 3 billions operations are being performed per second (this issometimes referred to as the clock speed of the computer).

Computer SpeedsThe number of calculations that a computer can perform is normally a goodindicator of the power of a computer:

1 Mhz (Megahertz) means that the processor can do 1 millionoperations per second

1 Ghz (Gigahertz) means that the processor can do 1 billionoperations per second

However, it is important to note that speed is not everything when

evaluating the performance of a computer!

There are two major manufacturers of processors for Personal Computers:AMD (Advanced Micro Devices) and Intel (Integrated Eletronics).


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Figure 2-3 Intel Pentium 4 (left) and AMD Processor (right)

A processor is a very compact device. It contains millions of transistorsarranged compactly, very very close to each other. For example, a Pentium 4processor contains 55 millions transistors1 . These transistors will worktogether to allow the CPU (Central Processing Unit another name forprocessor) to process information.

The CPU is made up of two main parts:

ALU (Arithmetic and Logic Unit) which performs mathematicalcalculations

Control Unit which controls the operations of the computer

Figure 2-4 Detailed Block diagram of the Computer System

In addition to those, the processor contains registers, which are small

memory units located inside the processor itself. These store intermediateresults of calculations.

To process data, the Fetch-Execute-Cycle is used sometimes called Fetch-Decode-Execute Cycle. The processor is always looping through this cycle.For example, to add two numbers, the Fetch-Execute-Cycle is executed asfollows:
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Fetch:

o the add instruction ( + ) and the operands (the numbers to be added)are fetched from memory and stored in the registers (all data andinstructions in a computer are stored in memory)

Decode:o the add instruction is then decoded - this is done by the Control Unitwhich sends appropriate signals

Execute:

o the ALU will then perform the addition operation

2.2.1.1 Data representationData inside the computer is represented as a series of 0's and 1s, which arecalled bits. A bit is either a 0 or a 1. Bits can be grouped into bytes; a byteconsists of 8 bits and bytes can then be grouped into Kilobytes (KB) 1 KB =1024 bytes.Note: KB means 1024 bytes while kB means 1000 bytes

This grouping hierarchy is best shown in the Table 2-1 below:

1 Byte 8 Bits1 Kilobyte (KB) 1024 Bytes

1 Megabyte (MB) 1024 KB

1 Gigabyte (GB) 1024 MB

1 Terabyte (TB) 1024

Table 2-1 Data Classification

Inside the computer, both data and instructions are represented as 0s and 1sas this is the only thing that a computer understands.

Decimal and BinaryHuman beings have ten fingers and when we count, we use our fingers tocount in sets of ten. We use what is known as the decimal system (0, 1, 2,3, 4, 5, 6, 7, 8, 9).

The computer does not have any fingers; it uses digital electrical signalswhich can only be On (1) or Off (0). So the latter can only count in sets of


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two and so uses the binary system (0, 1).

Another number representation system is the hexadecimal system. Here wecount in sets of 16 (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F)

2.2.1.2 Trends in CPUsAccording to Moore's Law, the number of transistors in a processor issupposed to double every 18 months. For quite some years, this law hasbeen duly respected but since transistors are physical components made ofatoms and molecules, there is a limit to which they can be miniaturized.Eventually in the last few years, we have not been able to double thenumber of transistors as we would have liked to and so we have had to findnew ways to increase the power of processors. These new ways have comeunder the name Hyper-threading, Dual Core and 64-bit processors whichrepresent new ways of increasing the performance of processors.

HyperthreadingA processor can execute only one instruction at a time during the Fetch-execute-Cycle. However, with Hyper-threading, it is as if we have twoprocessors (though we have only one) and so two instructions can appear tobe executed at the same time.

Dual CoreA Dual-Core processor physically has two processors into one packing for aprocessor. So, this time, two operations can be really executed at the sametime.

64-Bit processorsPreviously micro-processors were referred to as 32 bits - the 32 bits refers tothe size of the registers (small memory units) in the processor. Recently Inteland AMD have introduced 64-bit processors the registers are now 64 bitslong instead of 32 bits long. Thus more data can be accessed directly frommemory and also accessing the data is faster.

64-bit processors and programsThough 64-bit processors can cope with 64-bit long instructions, we needprograms than create these 64-bit instructions. Right now (at the time thisbook is being written), only a few Operating Systems can create 64-bitinstructions and so 64-bit processors find themselves underused.

2.2.1.3 Cooling the processorProcessors have not only become more powerful in recent years but theyalso generate more heat. If we do not find a way of cooling them down, theywill eventually burn!


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Figure 2-5 Fan (black) on top of heat sink (grey)

So CPUs are normally equipped with a heat sink and a fan on top of the heatsink. The heat sink will be placed on top of the CPU and normally somethermal paste is spread over the processor to increase heat conductivity

between the latter and the heat sink.

Figure 2-6 Processor with thermal paste applied on top

Overclocking the CPUOverclocking means running your processor at a faster speed thandesignated by the manufacturer. E.g. a 1.5 Ghz CPU is made to run at 1.7Ghz. CPU are overclocked to get a performance gain but as they workharder (they get more tired), they heat up more and so need better heatdissipation mechanisms.

2.2.2 MemoryWhenever software is installed on a computer, the latter is placed on thehard disk of the computer. However, when that software is run (e.g. whenyou double-click on its icon), the latter has to be transferred to the memoryof the computer for the CPU to be able to execute it.Memory in a computer is in the form of RAM (Random Access Memory)modules. RAM can be purchased in the form of RAM sticks and it is normallymeasured in terms of its size (256 MB, 512MB, 1 GB,...). RAM is said to be


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volatile, meaning that, information stays here as long as the computer is onbut as soon as it is turned off, the information inside the RAM disappears.

2.2.2.1 Types of RAMThe current type of RAM memory used in computer systems is referred to as

DDR (Double Data Rate) RAM. It has replaced the old SD (SynchronousDynamic) RAM which was used some time back and it offers improvedperformance.DDR2 is the new type of RAM technology that is very likely going to takeover from DDR RAM. However, it seems that we will have to wait a few moreyears to see this taking place completely. Intel has already adopted theDDR2 standard while AMD is still using DDR for now.

RAM PerformanceThe performance of a RAM module does not depend only on its size. There

are other factors like the speed at which the data can be transferred fromthe RAM to the processor (the frequency). There's also the speed at whichthe data can be accessed inside the RAM.

Figure 2-7 SD, DDR and DDR2 RAM


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2.2.2.2 Cache Memory

The purpose of cache memory is to speed up a computer while keeping itsprice low. Cache exists in different forms in computer but it primarily refersto the small memory locations found on the processor.There are usually two levels of cache in the processor of a computer; theseare Level 1 cache (L1) and Level 2 cache (L2).When a program is being run, it will take data from the hard disk and place itin the RAM. RAM is closer to the CPU and is also faster to access but yet, it isstill slower than the processor. To speed things up even more, the data thatare going to be worked with are transferred from the RAM to the cache whichmeans that when a program is being executed by the CPU, the latter will lookfor information in the cache and not in the RAM.

The problem is that the cache is very small (we do not have a lot of space onthe processor to have a big amount of cache) and so cannot store a lot ofinformation. Therefore before trying to access data from the cache, we mustfirst check if it is there a cache hit. Else, we have a cache miss and weneed to go retrieve the data from the RAM.

Cache Size and processor performanceThe size of the cache is an important aspect that will determine the overallperformance of processor. The cache size usually quoted is that of the Level2. For example, the size of the cache on a Pentium 4 Northwood (the

codename for that processor) is 512 KB.

Cache memory is arranged in a hierarchy as shown below:

Figure 2-8 Cache Hierarchy

The table below shows the approximate size of each component.

Memory TypeSize


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L1 Cache ~ 16 KB

L2 Cache ~ 512 KB 2 MB

RAM 256 MB 2GB

Hard Disk 60 GB 200 GB

Table 2-2 Memory Type and Speed

Another domain where the term cache is often used is the web. Connectingto the Internet (especially on a 56 KB modem) is very slow and also the datathat we are trying to access might be for example in Hawaii making dataretrieval an even slower process. So to try to improve the speed of accessingthe page, that page can be stored in a web server in Mauritius the first timeit is accessed and the next time another user wants access to the samepage, the latters browser will not have to fetch the page from Hawaii butcan instead get it directly from the web server in Mauritius, thus speeding up

data access.

2.2.3 The MotherboardThe motherboard is at the heart of the computer; it links all the differentcomponents (processor, memory, graphics card,...) together.As can be seen from Figure 2.9, the motherboard is very complex andcontains many small parts welded on it. We will now have a look at some ofthese different components.

Figure 2-9 The Motherboard2

2.2.3.1 The socket connection
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This is where the processor is connected to the motherboard. Differentmotherboards accept different types of processors depending on the type ofsocket they have. For example, Pentium 4 processors are connected to amotherboard through socket 478 while Athlon XP processors areconnected through socket A (also known as socket 462).

Figure 2-10 Socket 478 (left) and socket 462 (right)

2.2.3.2 The North Bridge and South BridgeThe North Bridge and South Bridge are two controllers found on themotherboard.The North Bridge controls the exchange of data between the processor,memory and graphics card. It is a high speed component that is usuallyequipped with a heat sink and a fan.The South Bridge controls exchanges of data between the PCI slots (in whichwill be plugged in the sound card, modem,...) and the backing storage

devices.

North Bridge and South Bridge CoolingThe North Bridge and South Bridge are basically two small processors. Sowhen they work they tend to heat up and need cooling else they will burn.

2.2.3.3 Memory BanksThis is where the memory modules will be connected on the motherboard.Memory banks can be single (DDR) or double sided (DDR2) allowing eithersingle memory modules to be connected or requiring two memory modulesnext to each other respectively. The current trend in new motherboards is to

have dual channels.


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Figure 2-11 DDR slot

2.2.3.4 The AGP SlotThe AGP (Accelerated Graphics Port) slot is where the graphics card will beconnected to the computer. It is physically very close to the CPU and soallows rapid interchange of information. Current AGP slots found onmotherboards are referred to as 8x reaching a data transfer speed of2Gbps.

2.2.3.5 PCI SlotsPCI (Peripheral Component Interconnect) slots allow sound cards, networkcards and modems to be connected to the computer. They are inherentlyslower compared to the AGP slot (transfers are of the order of 133Mbps).

2.2.3.6 PCI ExpressThis is going to be the successor to AGP. It is available in different flavoursranging from 1x, 2x, 4x, 8x and 16x. They are going to be faster that PCI (1xoperates at 250 Mbps) and they have already started to replace AGP slots onmotherboard the 16x version has been reserved for graphics card and it isoperating at 8Gbps (4Gbps in each direction)

2.2.3.7 IDE ConnectorsThese connectors will allow Hard Disks, CD-ROM and DVD-ROM Drives to beconnected to the computer. Typically two devices can be connected to oneIDE through the use of IDE(ATA) cables.

Figure 2-12 IDE Cable

2.2.3.8 Serial ATA (SATA)This is the new technology that is slowly replacing parallel ATA (IDE)connectors especially for hard disks. SATA I runs at 1.5Gbps resulting in a


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maximum transfer rate of 150 MBps while SATA II runs at 3.0 Gbps resultingin a maximum transfer rate of 300 MBps.

Figure 2-13 SATA Cable

2.2.3.9 BusWhat is a bus?Bus lines are what connect the different components found on themotherboard together. Data is going to flow along these lines. So the size of

the bus and speed at which data can flow is a good indicator of theperformance of the motherboard the processor needs data to work and itneeds to get that data very quickly. Having a very fast processor and a verynarrow and slow bus is useless - the processor will be idle while waiting fordata to arrive.

Front Side BusThe Front Side Bus (FSB) is what actually connects the CPU to the memory,graphics card and other components of the motherboard together. Modernmotherboards typically have busses of size 64 bits and a bus frequency ofabove 100 MHz. For example, Pentium 4 has bus of frequency

100/133/200/266 MHz.

The speed of the CPU is determined by applying a multiplier to the FSB.For example, a processor running at 550 MHz might be using a 100 MHzFSB. This means there is an internal clock multiplier setting of 5.5; the CPU isset to run at 5.5 times frequency of the front side bus: 100 MHz x 5.5 = 550MHz. 3

So, by altering the speed of the FSB, we can achieve different CPU speeds.This is the basis behind overclocking a processor. The speed of the FSB andthe multiplier can be set by modifying the BIOS.

2.2.4 Graphics CardGraphics card are very important in modern computers their job is tohandle most of the graphics work that has to be done by the computer. Assuch, they will have a processor, (which is hidden under the heatsink and fanin Figure 2-14) also known as the Graphical Processor Unit (GPU) as well assome memory on the card to allow them to process graphical information.
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Graphics cards are manufactured by two main companies nowadays: nVidiaand ATI. Graphics card used to come with AGP connectors but the currenttrend is to have PCI Express graphics card.

Figure 2-14 ATI Radeon 9800 Pro

2.2.5 Flash ROMThe BIOS is stored in a component called the Flash ROM (Read OnlyMemory). Information stored in ROM is stored there permanently, meaningthat even when the computer is turned off, the information stays there, in

comparison to RAM which is volatile.There are several types of ROM memory:

PROM: Programmable Read Only Memoryo This type of ROM is programmed by a special device and informationwritten onto it is permanently stored there

EPROM: Erasable Programmable Read Only Memoryo This is a type of ROM that can be erased through exposure to ultra-violet light

EAPROM: Electrically Alterable Programmable Read Only Memoryo This type of ROM can be erased electronically but changes can onlybe made one bit at a time so it is considered to be slow and thusrarely used

EEPROM: Electronically Erasable Programmable Read Only Memoryo An electronically erasable type of ROM that is sometimes referred toas Flash ROM. It can be erased and rewritten to while it is inside thecomputer.


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Flashing the BIOSThe BIOS contains instructions used to start the computer (a smallprogram). Like any other programs, there are sometimes improvements

and corrections to be made to it. Flashing the BIOS is the operation ofreplacing the instructions stored on the ROM by a set of more efficientones.

2.2.6 CMOSThe Complementary Metal Oxide Semiconductor is a type of memory thatworks with the BIOS; it stores configuration information for the computer. Asmall battery is required since the CMOS needs a small source of power sothat it does not lose any information.The CMOS is what you can access on pressing the Delete key (or some

other key on the keyboard) when the computer is started. It is usually a bluescreen arranged into menus that will allow changes made to theconfiguration of the computer.

2.2.7 PortsThese are sockets that allow devices like keyboard, joystick, mouse andprinter to be connected to the computer. Different types of ports exist, eachoperating at different speeds and meant for different devices.


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Figure 2-15 Ports on a computer

The table below shows the different ports in a computer

Port Use

USB (Universal SerialBus)

Connect Printers, Digital cameras, Pen drives - 480Mbit/s (USB 2)

Firewire Connect camcoders, some harddisks - 400 Mbit/s

Serial PortConnect some types of modem currently beingreplaced by USB - 19200 bit/s

Parallel Port Connect printers - currently being replaced by USB

PS/2 PortKeyboards and mouse currently being replacedby USB

Video Port Connect VGA monitors to the computer

DVI Connect LCDs to the computer

ModemConnect computers to the Internet usually dial-upconnection.

Network port Connect computers to networks

Power Connect the computer to power supply

Table 2-3 Memory Type and Speed

USB ports are connectors which are often used to connect digital cameras,scanners, printers,... to the computer. The USB (Universal Serial Bus) 2.0allows transfer speeds of up to 480 Mbps.


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A technology similar to the USB is the FireWire which supports speeds of upto 800 Mbps.

Figure 2-16 FireWire (left) and USB (right) cables

2.2.8 Expansion CardsThis is a general term used to refer to printed circuit boards that can be

inserted into PCI slots on the motherboard of the computer. These cardsprovide additional functionalities to the computer, for example, dial upInternet access (modem), radio or TV on the computer (TV card)

2.2.8.1 ModemA modem is a device that allows a computer to be connected to the Internet.The modem can be an expansion card inserted on the motherboard of thecomputer or it can exist as an external device (external modem).56 Kb modems are typically used for dial-up access in Mauritius. If fasterconnection is required, ADSL modem or the recently introduced WiMax(wireless) modem can be used.

2.2.8.2 Sound CardThis is an expansion card that is plugged in on the motherboard that willallow us to have sound output. Speakers and Microphones are usuallyconnected to it.However, sound cards are very often integrated on the motherboardmeaning that a separate sound card is not required.

2.2.8.3 TV CardThis is an interesting option to add to a computer. Basically it will allow you

to listen to radio and watch TV on your computer. It will contain a few plugswhere an antenna can be connected for the radio and the TV. A softwareassociated with the card will allow for tuning of the different radio and videochannels.


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2.2.8.4 Network cardThis allows a computer to be connected to a network. Normal 10/100 MbEthernet network cards are available that will allow a PC to connect to anetwork (like what you see in some Cyber Cafes and the university labs).Another type of network card that is gaining a lot of popularity is the

Wireless network card. It allows a computer to be connected to a networkwithout requiring any physical cable.


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EXERCISES

MULTIPLE CHOICE QUESTIONS

1. How many bits are there in 1 Kilobyte?

(a) 8 bits(b) 1000 bits(c) 1024 bits(d) 8192 bits(e) 1048576 bits

2. Which of the following is not a type of RAM?

(a) DDR RAM(b) SD RAM(c) DDR2 RAM(d) EDO RAM(e) AMD RAM

3. A processor is connected to the motherboard through a

(a) Socket(b) Port(c) Bus

(d) PCI slot(e) Memory slot

4. Which of the following is NOT TRUE?

(a) USB cables can be used to connect printers and cameras to a computer(b) A network port allows computers to be connected to a network(c) Parallel ports allow monitors to be connected to a computer(d) PS/2 ports allow keyboard and mouse to be connected to the computer(e) FireWire can be used to connect camcoders and hard disks to thecomputer


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5. How would you represent the decimal value 26 in Hexadecimal?

(a) 26(b) 1A(c) 11010

(d) 10(e) A1

6. Which of the following is NOT TRUE about cache?

(a) L2 cache is faster than L1 cache(b) A cache miss indicates that the information we are looking for is not inthe cache(c) RAM can be thought of as a cache for the Hard Disk(d) L2 cache is bigger than L1 cache(e) The size of L2 cache is approximately between 512 KB and 2 MB

7. AGP 8x looks likely to be replaced by _______________ ports in the nearfuture.

(a) PCI(b) PCI Express(c) AGP 16x(d) ISA(e) SATA connectors

8. Which type of ROM is commonly used in modern PCs?

(a) PROM(b) EPROM(c) EAPROM(d) EEPROM(e) None of the above

9. Which of the following gives a list of memory in ascending order of speedaccess?

(a) RAM, Hard Disk, L1 Cache, L2 Cache

(b) L1 Cache, RAM, Hard Disk, L2 Cache(c) L1 Cache, L2 Cache, RAM, Hard Disk(d) L2 Cache, L1 Cache, RAM, Hard Disk(e) Hard Disk, RAM, L2 Cache, L1 Cache


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10. Which of the following is NOT a type of Personal Computer?

(a) Desktop computers(b) Laptops/notebooks

(c) PDAs(d) Minicomputer(e) None of the above

OPEN-ENDED QUESTIONS

1. Describe the importance of cache in a computer.

2. Compare and contrast the features of the latest Intel Processor and the

AMD Processor.

3. Compare and contrast among the PCI, AGP and PCI Express slots.

4. How can the BIOS on a computer be upgraded?

5. Identify the different ports on a computer and give an example of a use for

each of them.

6. What components would be most important in building a PC that wouldallow you to play the latest games? Discuss (Note: games are very greedy in

terms of graphics resources)

7. Why is heat bad for the computer? What can be done to cool down the

computer and the processor?

8. Suppose you want to assemble a PC to allow you to play the latest 3D

games. What minimal configuration would be required for such a computer?

9. What is the Front Side Bus? How can it be used to overclock a computer?

10. What expansion card would you require for each of the following?

(a) Allow you to watch TV on the computer

(b) Allow you to connect to the Internet

(c) Allow you connect to a network

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