Chapter 6

The System Unit

McGraw-Hill/Irwin Copyright © 2008 by The McGraw-Hill Companies, Inc. All rights reserved.

System Unit

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System Unit Types

•   Desktop System Units

•   Notebook System Units

•   Tablet PC System Units

•   Handheld Computer

System Units

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Electronic Data and Instructions

•   Data and instructions are representedelectronically

•   Two-state system or Binary System–   Off/on electrical states

–   Characters represented by 0s (off) and 1s (on)

–   Bits (0,1)

–   Bytes (8 bits)

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Binary Coding Schemes

•   Three types of binary coding schemes–   ASCII - American Standard Code for Information

Exchange

–   EBCDIC - Extended Binary Coded DecimalInterchange Code (for ancient IBM punch cards)

–   Unicode – handles languages with large numbersof characters

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Unicode

•   More than 100,000 characters, such as…

•   Rules to deal with things like directionality–   Left-to-Right, Right-to-Left (Arabic, etc.)

•   Still evolving, but in widespread use

•   UTF-8 is the common version of Unicode–   Backward compatible with ASCII

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• • • • 

System Board

Connects all components

Allows communication between devices

Main board or motherboard

Circuit boardelectronic components–   Sockets

–   Slots

–   Bus lines

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System Board

• Sockets: provide a connection point for small specialized electronic parts called chips.

• Slots: provide a connection point for specialized cards or circuit boards (modem card).

• Bus Line: provide pathways that support communication among the various electronic components that are either located on the system board or attached to system board.

Microprocessor

•   Central Processing Unit (CPU)

•   Two Basic Components–   Control unit

–   Arithmetic-logic unit (ALU)

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Clock speed

• Clock speed: which is related to number of times the CPU can fetch and process data and instruction in a second.

Processor Clock Speeds

Hertz – a measure of frequency (Hz)

Megahertz (MHz)

A million times a second (fast)

Gigahertz (GHz)

A billion times a second (faster!)

My laptop:

2.0 GHz

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Clock Speed

•   Kilohertz (thousand) millisecond–   Camera Flash Bulb

•   Megahertz (million) microsecond–   Radio Waves, slow electronics

•   Gigahertz (billion) nanosecond–   Microwaves, modern electronics

•   Terahertz (trillion) picosecond–   Research, fastest transistors

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Specialty Processors•   Coprocessors

–   Designed to improve specific computing operations–   Graphics coprocessors

•   Smart cards–   Credit card sized with an embedded chip–   Used by many universities

•   RFID tags–   Information chips–   Used for tracking purposes

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6-18

RFID Tags

•   Reader sends a pulse•   RFID tag responds

–   Sends back an ID number

"How would you like it if, for instance, oneday you realized your underwear wasreporting on your whereabouts?"—California State Senator Debra Bowen

Page 162

Passports / ID cardsImplantable MicrochipsTiming Racing EventsTraffic Monitoring / TollboothsProduct Tracking

Promotional ItemsLibrary BooksMuseum GuidesMedical / Patient IDs

Memory

•   Holding area for data, instructions, andinformation

•   Memory is contained on chips connected tothe system board

•   Types of memory chips–   RAM

–   ROM

–   CMOS

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6-20

Memory SizesMeasured in bytes

1 byte = 1 character

Kilobyte (KB or Kbyte)1,024 bytes (= 210)

Megabyte (MB or Mbyte)1,048,576 bytes ( = 1K x 1K)

Gigabyte (GB or Gbyte)1,073,741,824 bytes (= 1K x 1M)

Terabyte (TB or Tbyte)1,099,511,627,776 bytes (= 1K x 1G)

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Memory SizesMeasured in bytes

1 byte = 1 character

KilobyteAbout 1/2 page

Megabyte (MB or Mbyte)Novel (500 pages)

Gigabyte (GB or Gbyte)50 feet of shelf space

Terabyte (TB or Tbyte)All of Powell’s Bookstore (est.)

RAM

•   Random Access Memory (RAM) chips holdthe program and data–   Cache memory or RAM cache

–   Flash RAM or flash memory

•   Other types of RAM–   DRAM

–   SDRAM

–   DDR

–   Direct RDRAM

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Cache Memory

•   Inserted between processor and RAM

Processor(CPU)

MainMemory(RAM)

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Cache Memory

•   Inserted between processor and RAM

Processor(CPU)

CacheMemory(L1 or L2)

MainMemory(RAM)

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ROM

•   Read-only memory (ROM) chips are notvolatile and cannot be changed by the user

•   CPU can read, or retrieve data and programsbut the computer cannot write

•   Contain special instructions–   Needed to start a computer

–   Give keyboard keys their special capabilities

–   Put characters on screen

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CMOS

•   Complementary metal-oxides semiconductor(CMOS) chips provide flexibility for acomputer system

•   Contains essential information every time thecomputer is turned on–   Date and time–   Amount of RAM–   Type of keyboard

•   Content can be changed to reflect changes inthe computer system

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System Clock

•   Important measurement indicating speed–   Located on a small chip

–   Produces electrical beats

•   Synchronizes operations•   Expressed in gigahertz (GHz)

(billions of beats per second)

•   Faster clock speed, faster computer

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Expansion Slots and Cards

•   Allow for new devices to be added–   Open architecture

–   Slots provide for expansion

•   Expansion cards are also called …–   Plug-in boards

–   Controller cards

–   Adapter cards

–   Interface cards

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• • • • 

• • 

Commonly Used ExpansionCards

Graphics cards

Sound cards

Modem cards

Network interface cards (NIC)

PC cards (PCMCIA cards)

TV tuner cards

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TV Tuner Cards AndVideo Clips

•   Allows you to view your favorite TV showswhile running other applications such asExcel

•   Video can be captured to a file, added to aWeb page, attached to an email, or added toa class presentation

•   Relatively inexpensive and

easy to install

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Plug and Play

•   Set of hardware and software standardsdeveloped by Intel, Microsoft, and others

•   Creating devices that are able to configurethemselves when installed

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Bus Lines

•   Connect parts of the CPU to each other

•   Data roadway for traveling bits–   Measured as bus width

–   More lanes, faster traffic

•   Two basic categories–   System buses

–   Expansion buses

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Expansion Buses

•   Connects the CPU to other components onthe system board, including expansion slots

•   Principal types–   Industry Standard Architecture (ISA)

–   Peripheral Component Interconnect (PCI)

–   Accelerated Graphics Port (AGP)

–   Universal serial bus (USB)

–   FireWire buses (HPSB)

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Ports

•   Socket for connecting externaldevices

•   Ports can connect directly tothe system board or they canconnect to cards that areinserted into slots on thesystem board

•   Two Types–   Standard Ports Ports

–   Specialized Ports

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Standard Ports

•   Four common ports–   Serial ports

–   Parallel ports

–   USB ports

–   FireWire ports

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Specialized Ports

•   Three specialized ports–   Musical Instrument digital interface (MIDI)

–   Infrared data association (IrDA)

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Cables

•   Used to connect exterior devices to thesystem unit via the ports

•   One end of the cable is attached to thedevice and the other end has a connectorthat is attached to a matching connector onthe port

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Power Supply

•   Computers require direct current (DC)

•   DC power provided by converting alternatingcurrent (AC) from wall outlets or batteries

•   Desktop computers use power supply units

•   Notebooks and handhelds use AC adapters

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