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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.

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the components in the system unit chapter 3

The Components in the System Unit, Chapter 3

ITSC 1401

Instructor: Glenda H. Easter

  • 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.
  • 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.
objectives continued
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.
overview of this chapter
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.
the system unit
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

the motherboard or the system board
The Motherboard or the System Board
  • CPU
  • Memory
  • Expansion Slots
  • Ports
the motherboard
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.
the most important chip the cpu
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).
cpu the brain of the computer
CPU (The Brain of the Computer)

Two parts:

  • ALU (Arithmetic/Logic Unit)
  • CU (Control Unit)
central processing unit
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.
parts of the cpu
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.
the control unit
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.
the control unit1
The Control Unit
  • The Control Unit controls the flow of data intoand from the Central ProcessingUnit
functions of the control unit
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.
machine cycle or instruction cycle
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.
the arithmetic logic unit alu
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.
  • 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.
  • 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.
system clock
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.
the system clock
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.

microprocessor chips
Microprocessor Chips
  • Intel
    • 486
    • 586
  • Motorola
    • 68030
    • 68040
  • DEC
processing chip
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.
microprocessor comparison
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.
microprocessor comparison continued
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.
microprocessor comparison continued1
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.
processor installation and upgrades
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.

CPU Manufacturers

  • Intel
  • Motorola
  • AMD
  • Cyrix

CPU Models

  • 8086 1978
  • 8088 1979
  • 80286 1982
  • 80386 1985
  • 80486 1989
  • Pentium 1993
  • Pentium Pro 1995
  • Pentium II 1997
  • Pentium III 1999
processor upgrades
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.
heat sinks and heat pipes
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.
data representation
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.

Computers Represent Data

With Electrical Switches

= 1

On-off circuits are simple

and are not prone to errors.

= 0

0 1 0 0 1 0 0 0

One byte is made up of 8 bits.

(binary 01001000 = decimal 72)

(ASCII 01001000 = the letter “H”)

three principal binary coding schemes
Three Principal Binary Coding Schemes
  • 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.
ascii american standard code for information interchange code
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.
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.
ebcdic extended binary coded decimal exchange code
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.
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.
  • 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.
a bit about bytes
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.
a parity bit
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.
a parity bit continued
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.
internal memory
Internal Memory
  • RAM
  • Virtual Memory
  • Cache Memory
  • ROM
  • 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
the capacity of memory
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.
  • 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.
ram random access memory
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.
ram continued
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.
random access memory
Random Access Memory
  • In RAM, each memory location has an address, just like a post office box.


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.
ram memory
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
ram expanded memory
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
ram extended memory
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
      • Ensures that two programs don’t try to use the same memory space
  • Access to extended memory relatively fast
ram extended memory continued
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 DOS-High command
ram memory1
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.
four types of ram memory continued
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.
virtual memory
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.
cache memory
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.
cache memory continued
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.
cache cache and more cache
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
cache cache and more cache continued
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.
cache cache and more cache continued1
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.
internal external and memory cache
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.
internal external and memory cache continued
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 high-speed holding area between the memory and the CPU.
cache cache and more cache1
Cache, Cache, and MoreCache
  • Compare looking for a document in cache similar to looking for a document in your office.
cache is your personal organizer
Cache Is Your PersonalOrganizer
  • When you need information in your office, you first look on yourdesk. 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.
cache is your personal organizer continued
Cache Is Your PersonalOrganizer (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.
cache is your personal organizer continued1
Cache Is Your PersonalOrganizer (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.
read only memory rom
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.
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.
two variations of rom
Two Variations of ROM
  • PROM: Programmable Read-Only Memory. Once this is written, it cannot be changed.
  • EPROM: Erasable Programmable - Read-Only Memory. Instructions on this chip can be erased with a special ultraviolet light, and then new instructions can be written on it.



Hard drive

expansion card or adapter
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

Plug and Play



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.

flash memory or flash rom
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.
  • 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
memory access time
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 - ameasure of how long it takes the device to read or write a given amount of data.
ports on the motherboard
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.
ports on the motherboard continued
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.
universal serial bus port
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.
all those ports
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.
all those ports continued
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.


Freeways for Data

Circuits that carry data from one component to another are called buses. The wider the bus, the more quickly the data can flow



data bus
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
the data bus
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.
bus lines
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.
bus width
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.
bus speed
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.
  • 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.
bays continued
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.
power supply
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.
power supply1
Power Supply
  • Converts AC (115 to 120 volts) to DC (5 to 12 volts)
  • Some peripheral devices have an AC adapter
laptop computers
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
summary of the components in the system unit
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
company on the cutting edge
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