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Copyright © 2003 Prentice Hall, Inc
Slides created by Bob Koziel
COMPUTERS IN YOUR FUTURE 2004
by Bryan Pfaffenberger and Bill Daley
Chapter 2
Inside the System Unit
Chapter 2
What You Will Learn
Inside the System Unit
 Description of the data computers transfer or store
 Components found inside the system unit
 Components found on the motherboard
 How the CPU processes data
 Characteristics of a microprocessor’s performance
 Types of memory
 Purpose and types of expansion buses
 Differences between analog and digital electrical
impulses
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Describing Hardware Performance
OFF
ON
OR
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= 1 bit
1
= 1 Byte
OR
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 Hardware performance refers to the amount of data a computer can
store and how fast it can process the data.
 Bit (Binary digit)– On or off state of electric current; considered the
basic unit of information; represented by 1s and 0s (binary numbers).
 Byte– Eight bits grouped together to represent a character (an
alphabetical letter, a number, or a punctuation symbol); 256 different
combinations.
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Millions, Billions, and More
8 bits = 1 Byte
1024 Bytes = 1 Kilobyte (KB)
1,048,576 Bytes = 1 Megabyte (MB)
1,043,741,824 Bytes = 1 Gigabyte (GB)
1,099,511,627,776 Bytes = 1 Terabyte (TB)
 Kilobyte, megabyte, gigabyte, and terabyte are terms
that describe large units of data.
 Data storage is measured using these terms.
Example: 20 GB hard drive
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Millions, Billions, and More
1000 bits = 1 kilobit (kb)
1,000,000 bits = 1 megabit (mb)
1,000,000,000 bits = 1 gigabit (gb)
 Kilobits, megabits, and gigabits are terms that
describe units of data.
 Used for measuring data transfer rate (bits per
second). Example: 56 kbps
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The System Unit
 The system unit is boxlike case that houses the
computer’s main hardware components.
 Space taken up on the desk is called a footprint.
 Form factor refers to how the internal components
are mounted in the unit.
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Types of System Units
Desktop
Notebook
Personal Digital
Assistant
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Inside the System Unit
 Motherboard (mainboard)– Large printed circuit
board with thousands of electrical circuits
 Power supply– Transforms alternating current (AC)
from wall outlets to direct current (DC) needed by the
computer
 Cooling fan– Keeps the system unit cool
 Internal Speaker– Used for beeps when error is
encountered
 Drive bays– Housing for the computer’s hard drive,
floppy drive, and CD-ROM / DVD-ROM drives
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The Motherboard
Microprocessor
Keyboard /
Mouse Ports
Printer Port
Click on terms to
view larger images
and information
Memory
Slots
Video Port
AGP Slot
PCI Slots
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Chipset
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Components of the CPU
 Control unit– Coordinates and controls all
parts of the computer system.
 Arithmetic-Logic unit– Performs arithmetic or
logical operations.
 Registers– Store the most frequently used
instructions and data.
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CPUs at Work
 Control Unit– Manages four basic operations (fetch,
decode, execute, and write-back).
 The machine cycle or processing cycle:
• Instruction Cycle
 Fetch- Gets next program instruction from the
computer’s memory.
 Decode- Figures out what the program is telling the
computer to do.
• Execution Cycle
 Execute- Performs the requested action.
 Write-back (Store)- Writes (stores) the results to a
register or to memory.
 Arithmetic-Logic Unit (ALU)– Performs basic
arithmetic or logic operations.
 Adds, subtracts, multiplies, and divides
 Compares data to determine which one is larger or smaller.
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The Processing Cycle
Click to
animate.
Click one
time only
ALU
Control unit
Memory
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Microprocessor Performance
 Data bus width– The number of pathways within the CPU that
transfer data (8, 16, 32, or 64)
 Word size– The maximum number of bits of data that the CPU
can process at a time (8 bits, 16 bits, 32 bits, or 64 bits)
 Operations per cycle (clock speed)– The number of clock
cycles per second measured in Megahertz (MHz) or Gigahertz
(GHz).
 Superscalar– Carrying out more than one instruction per
clock cycle.
 Pipelining– Feeding a new instruction into the CPU at every
step of the processing cycle.
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Parallel Processing
 Parallel processing involves using more than
one CPU to improve performance.
 Complex instruction set computer (CISC)– A
chip that includes special-purpose circuits
that carry out instructions at high speeds.
 Reduced instruction set computer (RISC)– A
chip with a bare-bones instruction set that
results in a faster processing speed than
CISC chips.
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Popular CPUs (of days gone by)
Intel
Pentium IV
Pentium III
Advanced
Micro Devices
(AMD)
Pentium MMX
Cyrix
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Motorola (Apple)
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Memory
RAM
Flash
ROM
 Memory is a term for a device that enables the
computer to retain (store) information.
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Memory Modules
DIMM
RIMM
NOTEBOOK
DIMM
SIMM
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Memory Categories
 Volatile memory– Contents of memory are erased
when power supply is turned off. It is temporary
storage.
 RAM– Random access memory holds data in locations
called memory addresses.
 Cache memory– Memory that the processor uses to store
frequently used instructions and data.
 Virtual memory– The computer uses the hard disk as an
extension of RAM.
 Nonvolatile memory– Contents of memory are not
erased when power is turned off.
 ROM– Read-only memory provides the instructions to start
the computer.
 Flash memory– Memory that can be rewritten.
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Random Access Memory / RAM
 RAM is a type of volatile memory that stores
information temporarily so that it’s available to the
CPU.
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HOW RAM WORKS
MONITOR
WEB
CLICK TO BEGIN
ANIMATION
RAM
KEYBOARD
CPU
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2003
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Prentice
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Hall,
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Virtual Memory
FULL
 Virtual memory involves:
 Part of the hard disk is reserved as RAM.
 When RAM modules become full, the CPU accesses the
hard disk to store and retrieve data.
 Slower than RAM.
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BIOS and CMOS
 BIOS– Basic input/output system is stored in ROM.
 Its instructions provide the boot sequence when starting the
computer.
 The boot sequence includes:
• POST– Power-on self-test checks memory and configures
video and other hardware.
• Locating the disk drive with the boot sector which contains the
operating system.
 CMOS– Complementary metal-oxide semiconductor
is a type of memory which stores essential startup
options.
 It stores the amount of memory installed and tracks date
and time.
 It is volatile.
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Cache Memory
 Primary cache (Level 1 or L1)– Located within the
CPU chip, it is the memory the microprocessor uses
to store frequently used instructions and data.
 Secondary cache (Level 2 or L2; Backside Cache)–
Located near the CPU, it is the memory between the
CPU and RAM.
 It is faster than RAM.
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Chipset
 A chipset is a collection of chips that work together.
 It provides circuitry to move data to and from the
rest of the computer.
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Input/Output (I/O) Buses
Expansion slots
Expansion card
 I/O buses are pathways that enable the CPU to
communicate with input/output devices.
 Typically the buses contain slots, called expansion
slots, in which expansion cards are inserted.
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Outside the System Unit
Drive bays
On/off switch
Reset button
BACK
Indicator lights
FRONT
 Power switch– Is located on the back. It turns power on/off to the
computer.
 Receptacles– Also called connectors or ports, are located on the back to
plug in peripheral devices, keyboard, mouse, and monitor.
 Front panel– Contains drive bays, various buttons, and lights.
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Types of Ports
Click on a port below to view information about it.
Click again to remove the text.
Sound
PS/2
Universal
Serial
Parallel
VGA
Game
connector–
port
port–
card
port–
(mouse
(keyboard
Serial
Data
connectors–
A Data
connector
Bus
A
flows
port)–
15
flows
port)–
(USB)–
pin
inSpecial
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through
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connector
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mini-plugs.
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Microphone,
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slow
a data
time.
data
simultaneously;
transfer
line-in,rate.
line-out,
faster
and
than
speaker
serial connectors
ports.
are used.
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The difference between serial and parallel ports
SERIAL
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PARALLEL
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How a Computer Represents Data
Analog
Digital
OFF
ON
 Computers represent data through electronic signals
or impulses.
 Two types of signals:
 Analog– Continuous waveform. Examples: talking and
computerized gas pumps
 Digital– On/off electrical states (bit). Examples: light
switches and transistors
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Character Codes
 Numerical data, that computers use;
translated into characters readable by
humans.
 American Standard Code for Information
Interchange (ASCII)– Eight bits; used by
minicomputers and personal computers
 Extended Binary Coded Decimal Interchange
Code (EBCDIC)– Eight bits; used by
mainframe computers
 Unicode– Uses 16 bits; over 65,000
combinations
=4
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=A
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Chapter 2 Summary
1. The basic unit of information is the bit.
2. Large units of data are kilobyte (KB), megabyte (MB),
gigabyte (GB), and terabyte (TB).
3. The motherboard is a circuit board that provides
receptacles for chips and input/output buses.
4. The central processing unit (CPU) contains the control
unit (CU) and the arithmetic-logic unit (ALU). It manages
the four basic operations (fetch, decode, execute, and
write-back).
5. The CPU’s performance is measured by the data bus
width, operations per second, speed, and cache memory.
6. Random access memory (RAM) is the computer’s main
memory. It is volatile.
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Chapter 2 Summary cont.
7. There are various types of RAM. They include dynamic RAM
(DRAM), synchronous DRAM (SDRAM), Rambus DRAM
(RDRAM), and double data rate (DDR)SDRAM.
8. Peripheral devices connect to the computer on the outside
of the case.
9. Computers have ports such as serial ports, parallel ports,
SCSI ports, USB ports, FireWire ports, and IrDA ports to
connect input/output devices.
10. Analog computers measure and digital computers count.
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THE
END
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