Chapter 2

The Components The Components of the System Unitof the System Unit

Prepared By: Humeyra Saracoglu

The System Unit

What is the system unit? Case that contains

system unit

electronic components of the computer used to process datato process data Sometimes called

the chassissystem unit

system unit

system unit

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The System Unit

What are common components inside the system unit? Processor power supply drive bays Memory Adapter cards Sound card

drive bays

processor

Sound card Modem card Video card

portsmemory

Network card Ports Drive bays sound card Drive bays Power supply

video card

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video cardmodem cardnetwork card

The System Unit

What is the motherboard? Main circuit

processor chipadapter cards

board in system unitC t i d t Contains adapter cards, processor chips, and

memory chips

c ps, dmemory chips

Also calledmemory slotssystem board memory slots

motherboard

Expansionslots for adapter cards

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The System Unitd l i li

What is a chip?dual inline packages (DIP) holds memory chips

Small piece of semi-conducting p gmaterial on which integrated circuits are etched

I t t d i it t i Integrated circuits contain many microscopic pathways capable of carrying electrical

pin grid array (PGA) package h ld

current Chips are packaged so they can

be attached to a circuit board holds processor chips

Click to view animation

be attached to a circuit board

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Click to view animation

Central Processing Unit

PP

What is the central processing unit (CPU)? Interprets and carries ProcessorProcessor

Control Control UnitUnit

Arithmetic Arithmetic Logic Unit (ALU)Logic Unit (ALU)

Arithmetic Arithmetic Logic Unit (ALU)Logic Unit (ALU)

Interprets and carries out basic instructions that operate a computer

Control Control UnitUnit

Control unit directs andInformationInformation

DataDataInformationInformation

Control unit directs and coordinates operations in computer Arithmetic logic unit

InputInputDevicesDevices

OutputOutputDevicesDevicesMemoryMemoryDataData InformationInformation

Arithmetic logic unit (ALU) performs arithmetic, comparison, and logical operations

InformationInformationDataData

InformationInformation

and logical operationsAlso called the processor

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StorageStorageDevicesDevices

Central Processing Unit

What is a machine cycle? Four operations of the CPU comprise a machine cycle

Step 1. FetchObtain program instructionor data item from memory

p p y

MemoryStep 2

Processor

Step 2.DecodeTranslate instruction into commands

Step 4. StoreWrite result to memory

Processor

Control UnitALUcommands

Step 3. ExecuteCarry out command

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The CPU Machine Cycle

Fetch The program’s binary code is “fetched” from its

temporary location in RAM and moved to the CPU.D dDecode The program’s binary code is decoded into commands

that the CPU understands.Execute The ALU performs the calculations. “Inside the Chip” by

IntelStore The results are stored in the registers.

Video Clip

Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall

Making Computers Faster

Pipelining: The CPU processes more than one i i iinstruction at a time

Nonpipelined CPU

Fetch Decode Execute Store

Fetch Decode Execute Store

Instruction 1

Instruction 2

Nonpipelined CPU

Fetch Decode Execute Store Instruction 1

Pipelined CPU

Fetch Decode Execute Store

Fetch Decode Execute Store

Fetch Decode Execute Store

Instruction 2

Instruction 3

Instruction 4 Fetch Decode Execute Store Instruction 4

Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall

Cache Memory

Small amount of memory ylocated on or near the CPU chip Stores recent or frequently used instructions and dataUsed for quick access byUsed for quick access by the CPUDifferent levels of cachee e eve s o c c e

Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall

Central Processing Unit

What is a register? Temporary high-speed storage area that holds p y g p g

data and instructions

Stores location Stores location from where instruction from where instruction

was fetchedwas fetchedStores Stores

instruction while it is instruction while it is being decodedbeing decoded

Stores data Stores data while ALU while ALU computes itcomputes it

Stores results Stores results of calculationof calculation

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Central Processing Unit

How do personal computer processors compare?Comparison of Widely Usedp y

Personal Computer ProcessorsName Date Clock

Introduced Speed®Itanium 2 2002 1 GHZ and up

Xeon 2001 1.4–2.4 GHZ

Itanium 2001 733–800 MHZ

P i 4 2000 1 4 2 53 GH

®

™®®Pentium 4 2000 1.4–2.53 GHZ

Pentium III Xeon 1999 500–900 MHZ

Pentium III 1999 400 MHZ–1.2 GHZ

Celeron 1998 266 MHZ 1 8 GHZ

®

® ™

®®Celeron 1998 266 MHZ–1.8 GHZ

Operon 2003 To comeAthlon MP 2002 1.53–1.6 GHZ

Athlon XP 2001 1.33–1.73 GHZ

®™

™

™Click to view video

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Athlon 1999 500 MHZ–1.4 GHZ™

Data Representation

How do computers represent data? Most computers are digital

Recognize only two discrete states: on or off

p g

discrete states: on or off Use a binary system to

recognize two statesU N b i h Use Number system with two unique digits: 0 and 1, called bits (short for (binary digits)

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Data Representation

What is a byte? Eight bits grouped together as a unitg g p g Provides enough different combinations of 0s and 1s

to represent 256 individual charactersb Numbers

Uppercase and lowercaseand lowercase letters

Punctuation marks

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Data Representation

How is a letter converted to binary form and back?Step 1.

St 2p

The user presses the capital letter D(shift+D key) on the keyboard.

Step 2.An electronic signal for the capital letter D is sent to the system unit.

Step 3S Step 3.The signal for the capital letter Dis converted to its ASCII binary code (01000100) and is stored in memory for processing.

Step 4.After processing, the binary code for the capital letter D is converted to an image, and displayed on the output device

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y p gdisplayed on the output device.

Memory

What is memory? Electronic components that

Seat #2B4 Seat #2B3

store instructions, data, and results

Consists of one or Consists of one or more chips on motherboard orth i it b dother circuit board

Each byte stored in unique location called an address, similar to addresses on a passenger train

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on a passenger train

Memory

How is memory measured? By number of bytes available for storage

Term Abbreviation Approximate Size

y y g

Kilobyte KB or K 1 thousand bytesMegabyte MB 1 million bytesGigabyte GB 1 billion bytesTerabyte TB 1 trillion bytesTerabyte TB 1 trillion bytes

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Memory

What is random access memory (RAM)?

Memory chips that can be Memory chips that can be read from and written read from and written

to by processorto by processor

Also called Also called main memorymain memory

oror primaryprimary

Most RAM is Most RAM is volatilevolatile, it is lost , it is lost when computer’s when computer’s

y py p

The more RAM aThe more RAM a

or or primary primary storagestorage power is power is

turned offturned off

The more RAM a The more RAM a computer has, the computer has, the faster it respondsfaster it responds

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Memory

How do program instructions transfer in and out of RAM?Step 1. When you start the computer, certain operating system files load into RAM from the

RAM

operating system files load into RAM from the hard disk. The operating system displays the user interface on the screen.

Operating system Operating system instructionsinstructions

Operating system Operating system interfaceinterface

Step 2. When you start a Web browser, the program’s instructions load into RAM from the

Web browser Web browser instructionsinstructions

Web browser Web browser windowwindow

hard disk. The Web browser window is displayed on the screen.

Step 3. When you start a word processing program, the program’s instructions load into RAM f th h d di k Th d i

Word processing Word processing program instructionsprogram instructions

Word processing Word processing program windowprogram window

RAM

RAM from the hard disk. The word processing program, along with the Web Browser and certain operating system instructions are in RAM. The word processing program window is displayed on the screen.

Step 4. When you quit a program, such as the Web browser, its program instructions are removed from RAM. The Web browser no longer is displayed on the screen.

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Web browser program Web browser program instructions are instructions are

removed from RAMremoved from RAM

Web browser Web browser window no longer is window no longer is

displayed on displayed on desktopdesktop

Memory

How much RAM do you need? Depends on type of applications you intend to runp yp pp y

on your computerRAM 128 to 256 MB 256 to 1 GB 1 GB and up

Use • Home and businessusers managingpersonal finance

• Using standard

• Users requiring more advanced multimedia capabilities

• Running number-intensiveaccounting, financial, or

• Power users creating professional Web sites

• Running sophisticatedCAD, 3D design, or

application softwaresuch as word processing

• Using educational or entertainment

spreadsheet programs• Using voice recognition• Working with videos, music, and

digital imaging

other graphics-intensive software

or entertainmentCD-ROMs

• Communicating with others on the Web

digital imaging• Creating Web sites• Participating in video conferences• Playing Internet games

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Memory

What is read-only memory (ROM)?M hi th t tM hi th t t ii i ii iMemory chips that store Memory chips that store

permanent data permanent data and instructionsand instructions

Nonvolatile memoryNonvolatile memory, it is not , it is not lost when computer’s lost when computer’s

power is turned offpower is turned off

Three types:Three types:

FirmwareFirmware——

EEPROMEEPROM((eelectrically lectrically

eerasable rasable pprogrammable rogrammable rreadead--oonly nly mmemory)emory)——

Type of PROMType of PROMManufactured with Manufactured with permanently written permanently written data, instructions, data, instructions, or informationor information

Type of PROM Type of PROM containing microcode containing microcode

programmer programmer can erasecan erase

PROMPROM((pprogrammable rogrammable

rreadead--oonly nly mmemory)emory)——y)y)

Blank ROM Blank ROM chip onto which chip onto which a programmer a programmer

can write permanentlycan write permanently

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Ports

What are ports and connectors? Port connects external devices to system unit Connector joins cable to peripheral

Available in one of two genders: male and female

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Buses

What is a bus? Channel that allows devices

i idinside computer to communicate with each other System bus connects processor

and RAM Bus width determines number

of bits transmitted at one time Word size is the number of

bits processor can interpret and execute at a given time

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