Transcript The Components in the System Unit, Chapter 3

The Components in the
System Unit, Chapter 3
ITSC 1401
Instructor: Glenda H. Easter
Objectives
 Identify the components in the system unit
and explain their functions.
 Explain how the CPU uses the four steps of
a machine cycle to process data.
 Compare and contrast various
microprocessors on the market today.
 Define a bit and describe how a series of
bits are used to represent data.
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Objectives
 Identify the components in the system unit
and explain their functions.
 Explain how the CPU uses the four steps of
a machine cycle to process data.
 Compare and contrast various
microprocessors on the market today.
 Define a bit and describe how a series of
bits are used to represent data.
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Objectives (Continued)
 Differentiate between the various types of
memory.
 Describe the types of expansion slots and
expansion cards in the system unit.
 Explain the difference between a serial and
a parallel port.
 Describe how buses contribute to a
computer’s processing speed.
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Overview of This Chapter
 This chapter presents the components in
the system unit, describes how memory
stores data, instructions, and information,
and discusses the sequence of operations
that occur when a computer executes an
instruction.
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The System Unit
 The system unit is a
box-like case that
houses the electronic
components of the
computer that are
used to process data.
The system unit, exposed
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The Motherboard or the
System Board
 CPU
 Memory
 Expansion Slots
 Ports
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The Motherboard
 This is also called the system board. It contains
the CPU and some memory chips.
 The motherboard is the main circuit board of a
computer.
 The motherboard has expansion slots designed
for:
 Expansion cards
 Ports to enable the computer to
communicate.
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The Most Important Chip:
The CPU
 The motherboard in the system unit
contains many different types of chips.
 Of these, one of the most important is the
central processing unit (CPU).
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CPU (The Brain of the
Computer)
Two parts:
• ALU (Arithmetic/Logic Unit)
• CU (Control Unit)
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Central Processing Unit
 The CPU is the part of the computer that runs
the program or executes program instructions.
It is also known as the processor.
 The CPU is located on a single electronic
component called the microprocessor chip.
 The chip is housed in the system unit or
system cabinet.
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Parts of the CPU
 There are two parts of the Central
Processing Unit:
 The control unit
 The arithmetic logic unit
 The control unit tells the rest of the
computer how to carry out a program’s
instructions.
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The Control Unit
 The control unit contains the
microprocessor, memory, and storage
devices.
 It directs the control signals between the
CPU and input and output devices.
 The CPU directs movement of electronic
signals between memory and the ALU.
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The Control Unit
 The Control Unit
controls the flow
of data into
and from the
Central Processing
Unit
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Functions of the Control Unit
 The control unit directs and coordinates most
of the operations in the computer.
 For every instruction, the control unit repeats
a set of four basic operations:
–
–
–
–
“Fetching” an instruction
Decoding the instruction
Executing the instruction
Storing the result, when necessary
 These four operations comprise the machine
cycle or instruction cycle.
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Machine Cycle or Instruction
Cycle
 Fetching: The process of obtaining a
program instruction or data from memory.
This is called instruction time.
 Decoding: Translating the instruction into
commands the computer understands.
 Executing: Carrying out the commands.
This is called execution time
 Storing: Writing the result to memory.
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The Arithmetic-Logic-Unit
(ALU)
 The ALU is the device that performs
fundamental math operations such as
addition, subtraction, multiplication, and
division.
 The ALU also handles logical operations
that compare two pieces of data to see if
they are equal, less than, or greater than the
other.
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Pipelining
 In some instances, the computer only
processes a single instruction at a time.
When the CPU has to wait until one
instruction is complete before starting the
next instruction.
 With pipelining the CPU begins to execute a
second instruction before the first instruction
is completed. This results in faster
processing.
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Registers
 The computers have additional storage locations
in the control unit, and these are called registers.
 Registers are high-speed staging areas that hold
data and instructions temporarily during
processing.
 Functions of registers include storing the
location where an instruction was fetched,
storing an instruction while it is being
decoded, storing data while the ALU
processes it, and storing the results of a
calculation.
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System Clock
 A microprocessor’s speed is determined by two
major factors:
 bus speed
 clock speed
 The system clock controls how fast instructions
are processed and the speed of your system.
 The speed is measured in megahertz (MHz).
1 megahertz = 1 million beats (cycles) per
second.
 The speed affects only the CPU and has no
effect on peripherals.
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The System Clock
About MHz: the faster
the clock, the faster the
processing speed.
(1 MHz = 1 million clock
cycles per second)
The Pentium II has 7.5 million
transistors, more than double
the number included on the
original Pentium chip. It
can operate from 233 MHz to
400 MHz and beyond.
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Microprocessor Chips
 Intel
– 486
– 586
 Motorola
– 68030
– 68040
 DEC
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Processing Chip
 In a microcomputer, the central processing
unit is contained on a single silicon chip. This
is called the microprocessor chip.
 Processing chips include:
 Intel Chips used by IBM
 Motorola Chips used by Macintosh
 Digital Equipment Corporation Chips
used by minicomputers, mainframes, and
supercomputers.
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Microprocessor Comparison
 A microprocessor often is identified by its
model name or model number.
 Intel leads the manufacturers of processors.
 After learning the CPU numbers could not
be trademarked and protected from use by
competitors, Intel decided to identify their
microprocessors with names, not numbers.
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Microprocessor Comparison
(Continued)
 Pentium Processors is the number one leader in
microprocessor chips.
 Celetron is designed for less expensive PCs
 Xeon and Itanium are geared toward
workstations and servers.
 Motorola microprocessor which is found in
Apple Macintosh and Power Macintosh systems.
 Alpha microprocessor was developed by Digital
Equipment Corporation is used primarily in
workstations and high-end servers.
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Microprocessor Comparison
(Continued)
 A new type of microprocessor called an
integrated CPU, combines functions of a
CPU, memory, and a graphics card on a
single chip.
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Processor Installation and
Upgrades
 Processor chips are inserted into an
opening or socket on the motherboard.
 Most computers today have a ZIF socket
which is designed to facilitate the
installation and removal of processor chips.
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CPU Manufacturers
• Intel
• Motorola
• AMD
• Cyrix
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CPU Models
• 8086
1978
• 80486
1989
• 8088
1979
• Pentium
1993
• 80286
1982
• Pentium Pro 1995
• 80386 1985
• Pentium II
1997
• Pentium III 1999
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Processor Upgrades
 Processor upgrades take one of three forms:
– Chip for Chip Upgrade where the existing
chip is replaced with a new one.
– Piggyback Upgrade: A new processor chip is
stacked on top of the old one.
– Daughterboard Upgrade: A daughterboard
upgrade is a small circuit board that plugs into
the motherboard. It often adds additional
capabilities to the motherboard.
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Heat Sinks and Heat Pipes
 Newer processor chips generate a lot of heat
which could cause the chip to burn up.
 A heat sink is a small ceramic or metal
component with fins on its surface that is
designed to absorb and ventilate heat produced
by the electrical components.
 A heat sink consumes a lot of room; therefore, a
smaller device called a heat pipe is used to cool
laptop computers.
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Data Representation
 Computers can operate in only two states:
on and off.
 The on state is represented by one (1).
 The off state is represented by zero (0).
 Computers work totally with data that has
been encoded with 0 and 1 and is therefore
called the binary system.
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Computers Represent Data
With Electrical Switches
=1
=0
0
1
0
On-off circuits are simple
and are not prone to errors.
0
1
0
0
0
One byte is made up of 8 bits.
(binary 01001000 = decimal 72)
(ASCII 01001000 = the letter “H”)
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Three Principal Binary
Coding Schemes
 ASCII
 EBCDIC
 Unicode
 Each scheme groups binary numbers in a
different way; therefore, when files are
used or shared by different computers or
applications, they must use the same
coding scheme.
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ASCII (American Standard Code for
Information Interchange Code)
 ASCII is the most widely used binary code
for microcomputers.
 It is the code used on personal computers.
 Some application programs attach special
meanings to certain ASCII codes.
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ASCII
(Continued)
 These designated purposes include
formatting such as boldface and italics.
 For this reason, one program cannot read
data created in another program unless it is
translated to the other program’s codes.
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EBCDIC (Extended Binary
Coded Decimal Exchange Code)
 EBCDIC was developed by IBM and used on
many IBM and other kinds of computers.
 It is almost an industry standard for large
computers, especially mainframes.
 Although EBCDIC is slowly dying out, a
great deal of data stored on tape use EBCDIC
character set, so the need to have programs
convert from EBCDIC to ASCII is not going
away.
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EBCDIC versus ASCII
 EBCDIC was always an 8-bit character
code, and it could represent 256 characters.
 ASCII was initially a 7-bit character code,
so ASCII could only represent 128 distinct
characters.
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Unicode
 Unicode is a sixteen-bit code designed to
support international languages like
Chinese and Japanese.
 It was developed by Unicode, Inc. with
support from Apple, IBM, and Microsoft.
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A Bit about Bytes
 The smallest unit of measure is a nibble.
This is one-half of a bit.
 Today, both ASCII and EBCDIC use an
eight-bit coding system.
 ASCII added one bit for parity.
 An extra bit, called a parity bit, is
automatically added to each character’s
code in a computer system.
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A Parity Bit
 A parity bit is used to check for memory
or data communication errors. It verifies
the validity of data as it passes through the
electronic circuitry of the computer
components.
 A parity bit enables the computer to detect
an error, but does not tell the computer
how to correct the error.
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A Parity Bit (Continued)
 An even-parity bit system is set to either o
or 1 to ensure the number of 1s is even in
the byte.
 With an odd-parity bit system, the parity
bit is set to either 0 or 1 to ensure the
number of 1s is odd in the byte.
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Internal Memory
 RAM
 Virtual Memory
 Cache Memory
 ROM
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Memory
 Most computers use memory as scratch pads to
hold programs and data in use in the CPU.
 The four types of memory are:
 RAM
 Virtual
 Cache
 ROM
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The Capacity of Memory
 The capacity of memory is measured by
the number of characters of data or
instructions it can hold.
 Before you buy any software package,
check to see how much memory it requires
to run.
 You can add more memory by adding
memory chips.
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Addresses
 During the processing cycle, data or
instructions are placed in main memory
locations called addresses.
 Each address location is identified by a
unique number that always remain the same.
 Although the memory address numbers
always stay the same, the contents within the
addresses locations are continually changing.
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RAM
(Random-Access Memory)
 RAM is the internal storage area of the
system unit called memory of primary
storage.
 RAM holds the program and data that the
CPU is presently processing.
 RAM is temporary or volatile storage.
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RAM (Continued)
 Data and programs must be loaded into
RAM before they can be used by the
computer.
 RAM’s temporary storage capacity is
measured in terms of bytes.
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Random Access Memory
data
• In RAM, each memory location has an
address, just like a post office box.
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DRAM and SRAM
 Two basic types of RAM exist:
– Dynamic RAM (DRAM): This type of RAM
must be re-energized constantly or it loses its
contents.
– Static RAM (SRAM): It is faster and more
reliable than any form of DRAM. It does not
have to re-energized as often as DRAM.
– SRAM is much more expensive than DRAM.
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RAM Memory
 RAM is divided into sections.
 Conventional RAM - First 640 Kb
– DOS (about 130Kb)
– TSR programs
– Other DOS programs must run in this area
 Upper memory area- Next 386 Kb.
– Subdivided into 64 Kb Upper memory blocks
– Device drivers/system files which manage video and
other hardware
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RAM-Expanded Memory
 Original solution which gave PCs access to
RAM beyond 1 Mb
 Originally required an expansion card and
software
 Access to expanded memory slow
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RAM-Extended Memory
 Better solution to access RAM beyond 1
Mb
 Requires an extended memory manager(s)
– EMM386.EXE
• Provides access to the additional RAM
– HIMEM.SYS
• Ensures that two programs don’t try to use the
same memory space
 Access to extended memory relatively fast
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RAM- Extended Memory
(Continued)
 High memory area (HMA)-First 64 Kb of
Extended Memory
– DOS can be “forced” into this area to free up
additional conventional RAM using DOSHigh command
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RAM Memory
 Conventional - The first 640K of RAM
accessed by system and software.
 Upper - Located between 640K and 1MG
of RAM. It is usually used by DOS to
store information about the computer’s
hardware.
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Four Types of RAM Memory
(Continued)
 Extended - Accessible memory above
1MG. It is usually used by some programs
such as Windows.
 Expanded - Special “island” of memory of
up to 32 MB that exists outside of the DOS
640K limit. It was initially designed to
assist users of older 8086 and 8088
processors access memory beyond 640K.
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Virtual Memory
 Virtual memory is used to run very large
programs or two or more smaller programs,
without running out of memory.
 The computer can swap portions of the
program between the hard drive and RAM, as
they are needed.
 Virtual memory sounds great: more memory
for “free” assuming that you have disk space
left.
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Cache Memory
 Each time the CPU requests data from the
slower main memory, the computer places
a copy of the data in the faster memory
cache.
 Cache contains data that is most recently
used by the CPU.
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Cache Memory
(Continued)
 Cache reduces the time it takes to get information
from main memory.
 The CPU is the main chip that processes data in a
computer. The CPU gets data from internal
cache, external cache or main memory.
 If the CPU cannot find the data it needs in the
external cache, it looks in the slower main
memory or RAM.
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Cache, Cache, and More
Cache
 Used to store data and program code for
quicker access
 Internal Cache Memory (Designated as L1
Cache)
– Part of the CPU
– Internal Cache is very small and comprises
0-16K of storage
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Cache, Cache, and More
Cache (Continued)
 External Cache Memory (Designated as
L2 Cache)
– Referred to as SRAM (static RAM-higher
speed chips)
– SRAM is very high speed RAM chips.
– The typical SRAM is 64 to 512K
• The reason everything isn’t high speed is due to the
expense. They are a very expensive staging area
going into and out of CPU.
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Cache, Cache, and More
Cache (Continued)
 Disk Cache
– This is referred to as DRAM (Dynamic RAM) -
–
–
–
–
–
Designated as L3.
Faster than accessing data from the hard drive
Slower than accessing data from L1 or L2 cache
Contains frequently used data and or program
code
The computer decides what goes into Disk Cache,
but the user controls the size of disk cache.
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Internal, External
and Memory Cache
 Internal Cache (L1): When the CPU
needs data, it looks first in the internal
cache. This is the fastest.
 External Cache (L2): External cache or
secondary cache resides on the
motherboard. External cache is slower
than internal cache but much faster than
main memory.
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Internal, External and
Memory Cache (Continued)
 Main Memory cache: When information
can’t be found in internal nor external cache,
the computer looks to main memory cache.
 The computer decides which information is to
be copied to cache memory.
 Cache memory acts as a temporary highspeed holding area between the memory and
the CPU.
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Cache, Cache, and More
Cache
 Compare looking for a document in cache
similar to looking for a document in your
office.
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Cache Is Your Personal
Organizer
 When you need information in your office,
you first look on your desk. This is the
fastest way to find something. Think of
this as internal cache.
 If you can’t find the document on your
desk, you look in your desk drawer.
Compare this to external cache.
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Cache Is Your Personal
Organizer (Continued)
 If the information is not in your desk
drawer, you may have to go to the file
cabinet to retrieve the document. Think of
the filing cabinet as main memory cache.
This slows you down drastically.
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Cache Is Your Personal
Organizer (Continued)
 But can you imagine what it is like if you
don’t know where something is filed?
Having to look through everything in the
file cabinet is very time consuming. The
same is true without cache.
 Cache helps you maintain order.
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Read-Only Memory (ROM)
 ROM enables your computer to start again
without having everything erased.
 Some computers store ROM which has certain
basic operating procedures used after start-up.
 The instructions to start the computer are stored
in read-only memory chips (ROM).
 ROM is also called firmware.
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ROM
(Continued)
 ROM chips cannot be changed by the
users.
 ROM chips contain special instructions for
detailed computer operations to start the
computer, give keyboard keys their special
control capabilities and put characters on
the screen.
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Two Variations of ROM
 PROM: Programmable Read-Only
Memory. Once this is written, it cannot
be changed.
 EPROM: Erasable Programmable - ReadOnly Memory. Instructions on this chip
can be erased with a special ultraviolet
light, and then new instructions can be
written on it.
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Head
Hard drive
RAM
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Expansion Card or Adapter
 Expansion cards are designed to allow the
attachment of other peripheral devices;
therefore, expansion slots are located along
the back or side of the computer.
 Three types of expansion cards include:
– Video card
– Video adapter or graphics card
– Sound card
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Plug and Play
Module
A
Microsoft and Intel created the Plug and Play
(PnP) standard. This standard requires
special chips on the motherboard, compatible
hardware that is expressly compatible with
the Plug and Play standard, and a system
BIOS that supports Plug and Play.
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Flash Memory or Flash ROM
 Flash memory is another vo latile memory.
 It can be erased electronically and
reprogrammed.
 It is used to store programs on personal
computers, as well as cellular telephones,
printers, digital cameras, pagers, and
personal digital assistants.
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CMOS
 Used to store startup configuration options
such as:
 Disk drives, keyboard, monitor; the current
date and time
 Other startup information needed when the
computer is turned on.
 CMOS chips use batteries to maintain the date
and time when the computer is turned off.
 It can be changed.
 Each memory location has an address
 Volatile
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Memory Access Time
 Factors that Affect Drive Performance
– Average Access Time
– Data Transfer Rate
• Average Access Time - the average time it
takes a read/write head to move from one place
on the recording medium to any other place on
the medium.
• Data-transfer Rate - a measure of how long
it takes the device to read or write a given
amount of data.
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Ports on the Motherboard
 A port is a socket at the back of a
computer where you plug in an external
device.
 A serial port is known as a male connector
and this type of port connects a modem,
mouse, or scanner.
 A computer internally labels each serial
port with letters COM.
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Ports on the Motherboard
(Continued)
 A parallel port is known as a female
connector and this type of port is used to
connect printers.
 A parallel port is labeled with LPT.
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Universal Serial Bus Port
 USB ports can connect up to 127 different
peripheral devices with a single connector.
 A USB port connects to newer peripherals
such as digital cameras and joysticks.
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All Those Ports
 Midi Port: Musical Instrument Digital Port.
This will accommodate synthesizers.
 SCSI Port: Parallel port used to attach disk
drives and printers.
 1394 Port: FireWire can connect to multiple
types of devices requiring faster data
transmission such as that needed on a digital
video camcorder, and digital VCRs and color
printers.
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All Those Ports (Continued)
 IrDA Port: Some peripheral devices do
not use any cables; instead they transmit
data via infrared light waves. For these
wireless devices to transmit signals to a
computer, both the computer and the
device must have an IrDA port.
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Buses:
Freeways for Data
Module
A
Circuits that carry data
from one component to
another are called
buses. The wider the
bus, the more quickly
the data can flow
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Data Bus
 Data Bus Width & Word Size
 number of bits in bus determines word size
 16-bit CPU works with 16 bit word size
 CISC (complex instruction set computer)
 many instructions & special-purpose circuits
 RISC (reduced instruction set computer)
 bare-bones instruction set
 less expensive, more efficient
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The Data Bus
 The width of a CPU’s address bus
determines the maximum amount of memory.
 The CPU and the ALU, as well as other
components of the computer, are connected
by a bus which is a highway of parallel
wires.
 The bus is the electronic pathway in a
computer that carries information between
devices.
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Bus Lines
 Bus Lines or (simply bus) are data
roadways that connect parts of the CPU to
each other and the CPU to other important
hardware.
 A bus line resembles a multi-lane highway.
 Bits travel along the bus highway.
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Bus Width
 Bus width is similar to the number of lanes
on a highway.
 The greater the width, the more data that
can flow along the bus at a time.
 Width is measured in bits.
 Eight bits represent one character.
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Bus Speed
 Bus speed is similar to the speed limit on a
highway.
 The faster the speed, the faster data travels.
 Speed is measured in megahertz (MHZ).
 The speed of a computer is determined by:
 the system clock
 the bus width.
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Bays
 A bay is an open area inside the system
unit used to install additional equipment.
 Bays are not to be confused with expansion
slots, which is used for the installation of
expansion cards.
 Because bays most often are used for disk
drives, these spaces commonly are called
drive bays.
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Bays (Continued)
 Two types of drive bays exist:
– External drive bay or exposed drive bay
allows access to the drive outside the system
unit.
– Internal drive bay or hidden drive bay is
concealed entirely within the system unit.
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Power Supply
 Computers use DC power ranging from 5 to
12 volts.
 When plugged into standard wall outlets,
which supply an alternating current (AC) of
115 to 120 volts.
 The Power Supply converts the wall outlet
AC power into DC power.
 External peripheral devices have an AC
adapter.
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Power Supply
 Converts AC (115 to 120 volts) to DC (5 to
12 volts)
 Some peripheral devices have an AC
adapter
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Laptop Computers
 Used for mobile users
 Typically weighs four to ten pounds
 Include a system unit
– System unit has many other devices built into
it
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Summary of the Components
in the System Unit
 The system unit
 CPU and the microprocessor
 Data representation
 Memory
 Expansion slots and expansion cards
 Ports, Buses, Bays
 Power supply
 Laptop computers
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Company on the Cutting Edge
 Intel
– Started by Robert Noyce and Gordon Moore
in 1968
• Joined by Andy Grove
• 4004 was introduced in 1971
– 2,300 transistors
• IBM chose Intel 8088 for the IBM-PC in 1980
• Now employs over 60,000 people
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