computing
ESSENTIALS

4
The System Unit
Copyright 2003 The McGraw-Hill Companies,
Inc.
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computing

ESSENTIALS
Competencies
System unit types
Coding
Memory and chips
Cards and buses
Ports and cables
Copyright 2003 The McGraw-Hill Companies,
Inc.
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computing

ESSENTIALS
System Unit Types

System Unit
 Houses electronic
components
 Basic components
 System board
 Microprocessor
 Memory

Types of System
Units

Desktop

Notebook

Personal Digital
Assistant
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Inc.
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computing
ESSENTIALS

Desktop Units

Non-portable

Input/Output devices
located outside the
system cabinet
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computing

ESSENTIALS
Notebook Unit

Portable

Monitor attached by
hinges

Keyboard and
pointing devices
integral to the system
unit
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computing
ESSENTIALS

PDA Units

Smallest system unit

All input/output and
secondary storage devices
integral to the system unit
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computing
ESSENTIALS

Electronic Data & Code

Binary System

0s and 1s

Each 0 or 1 is a bit

8 bits = 1 byte
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computing
ESSENTIALS

Binary Coding Scheme

American Standard Code for Information
Interchange (ASCII)

Extended Binary Coded Decimal Interchange
Code (EBCDIC)

Unicode
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computing
ESSENTIALS

ASCII



Widely used in
microcomputers
1 byte = 1 character
Examples
 Letter R is represented
by 0101 0010
 Number 3 is
represented by 0011
0011
 Character % is
represented by 0010
0101
Copyright 2003 The McGraw-Hill Companies,
Inc.
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computing
ESSENTIALS

EBCDIC

Developed by IBM

Used in mainframe computers

1 byte = 1 character

Examples

Letter R is represented by 1101 1001

Number 3 is represented by 1111 0011

Character % is represented by 0110 1100
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Inc.
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computing
ESSENTIALS

Unicode

Developed by Unicode, Inc. with support from
Apple, IBM, and Microsoft

Used to support international languages such as
Japanese and Chinese

2 bytes = 1 character
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Inc.
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computing

ESSENTIALS
System Board

Connects all
components

Data path between
devices

Also called the main
board or motherboard
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computing
ESSENTIALS

System Board Components

Sockets
 Connection points on the system board

Chips
 Tiny circuit boards etched into silicon wafers

Carrier Package
 Connects mounted chips into sockets
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computing
ESSENTIALS

Microprocessor



The “brains” of the computer system
Location of the Central Processing Unit
(CPU)
Chip capacity expressed in word size
 16 bit, 32 bit, 64 bit
 Larger the word size
faster the computer
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Inc.
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computing
ESSENTIALS

CPU


Control unit
 Directs the movement of electronic signals
between memory and the ALU
Arithmetic-logic unit (ALU)
 Arithmetic operations
 Fundamental math operations
 Logical operations
 Compares data
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computing
ESSENTIALS

Common Microprocessors


CISC chip
 Complex Instruction Set Computer
 Intel’s Pentium, Itanium chips, AMD
Athlon, Hammer chips
RISC chip
 Reduced Instruction Set Computer
 Simpler, cheaper then RISC chips
 Motorola PowerPC chip, DEC Alpha
chip
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computing
ESSENTIALS

Other Microprocessors

Smart Cards

Plastic card that contains a specialized
processor chip

Stores more than 80 times data of
conventional magnetic strip

Used in credit cards, identification cards,
phone cards
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Inc.
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computing

ESSENTIALS
Memory


Holding area for data and
instructions
Three types
 Random-access memory
(RAM)
 Read-only memory
(ROM)
 Complementary metaloxide semiconductor
(CMOS)
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computing
ESSENTIALS

Random-access Memory



Holds currently running programs and data
being processed by the CPU
Volatile storage
 Contained data is lost when computer is
turned off
Virtual memory
 RAM pages saved to secondary storage until
needed by CPU
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computing
ESSENTIALS

Special RAM Types


RAM cache
 Frequently accessed data
 Acts as high-speed, temporary holding
area between CPU and RAM
 Faster processing results
Flash RAM
 Data is retained even if power disrupted
 Commonly used in cell phone, digital
cameras
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computing
ESSENTIALS

Read-Only Memory

Programs and data are permanently encoded

CPU can only retrieve data

Nonvolatile, cannot be changed by the user

Used for storing special instructions, such as
computer startup
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computing
ESSENTIALS

Complementary Metal-Oxide
Semiconductor

Provides the flexibility and expandability for a
computer system

Saves data even when computer power is shut
off

Contents can be changed by the user

Stores information such as amount of memory,
type of keyboard, mouse
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computing

ESSENTIALS
Memory Measure
Unit
Capacity
Kilobyte (KB)
1,000 bytes
Megabyte (MB)
one million bytes
Gigabyte (GB)
one billion bytes
Terabyte (TB)
one trillion bytes
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computing
ESSENTIALS

System Clock

Special chip that produces precise
electrical impulses

Used to coordinate and synchronize
computer operations

Expressed in megahertz or gigahertz

Faster clock speed, faster computer
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computing
ESSENTIALS

Expansion Slots

Slots provided to add expansion cards to the
system unit

Used on open architecture system boards
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computing
ESSENTIALS

Expansion Cards

Expansion cards used to connect to devices
outside the system unit

Controller cards, Adapter cards, Interface
cards, plug-in boards

Usually have ports to connect the card to a
device outside the system unit
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computing
ESSENTIALS

Types of Expansion Cards







Network interface cards
(NIC)
Modem cards
Sound cards
Video cards
SCSI adapter
TV tuner cards
PCMCIA cards
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ESSENTIALS

“Plug and Play”

Hardware and software standards


Makes system expansion easy for the user
Automatically installs drivers and system
configuration

System unit recognizes the new device
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computing

ESSENTIALS
Bus Lines


More lines, the faster
data can travel
 64 bit data bus is
faster than a 32 bit
Data pathways that
link parts of the CPU
together and
components to the
CPU
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computing
ESSENTIALS

Principal Bus Architectures

Industry Standard Architecture (ISA)

Peripheral Component Interconnect (PCI)

Advanced Graphic Port (AGP)

Universal Serial Bus (USB)

High performance Serial Bus (HPSB)
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computing
ESSENTIALS

ISA Bus

Developed by IBM for personal computers

Slow


Originally 8 bit, later expanded to 16 bit

Still used by some expansion cards
Replaced by PCI bus in the near future
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computing
ESSENTIALS

PCI Bus

Originally developed to meet demands of
graphical user interfaces

High speed


32 bit or 64 bit
Widely used to connect CPU, memory, and
expansion cards
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Inc.
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computing
ESSENTIALS

AGP Bus

Dedicated bus for acceleration of graphics
performance

Replacing the PCI bus for transfer of video data
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computing
ESSENTIALS

Other Bus Types


USB
 Connects directly to the PCI bus on the
motherboard
 Supports external devices without inserting
expansion cards for each device
HPSB
 FireWire
 Similar to USB but faster
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Inc.
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computing
ESSENTIALS

Ports


Sockets that connect
external devices to the
system unit
Four common port
types
 Serial
 Parallel
 USB
 FireWire
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computing
ESSENTIALS

Serial & Parallel Ports


Serial Port

Data sent one bit at a time

Good long distance transmission of data
Parallel Port

Data sent 8 bits simultaneously

Used for short distances
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Inc.
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computing
ESSENTIALS

USB and HPSB Ports


USB Port
 Replacing serial and parallel ports
 Faster
 Each port can support
more than one device
HPSB Port
 FireWire ports
 Faster then USB ports
Copyright 2003 The McGraw-Hill Companies,
Inc.
37
computing

ESSENTIALS
Cables

Connect
Input/Output devices

Mouse

Keyboard

Printer

Monitor

Newer cables
 AGP
 graphics monitor
 USB
 joy stick; scanner
 HPSB
 video camera
Copyright 2003 The McGraw-Hill Companies,
Inc.
38
computing
ESSENTIALS

Look to the Future


Wireless Technology and PDAs
Personal wearable computer
 POMA®
 Wireless pointing device, head
mounted display
 Developed by Xybernaut
Corporation
 Currently being evaluated for
use in airport security
Copyright 2003 The McGraw-Hill Companies,
Inc.
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Chapter 4: The System Unit