The System Unit

1
The System Unit

• Lecture 5

2
Competencies

• Describe how a computer uses binary codes to
  represent data in electrical form.
• Discuss each of the major system unit components.
• Explain the differences among the three types of
  memory.
• Discuss the three principal types of bus lines.
• Discuss five types of ports.

3
Introduction

• How are application programs executed within the
  computer system?
• Why are some microcomputers more powerful than
  others?
• Difference in speed, capacity, and flexibility of
  computers.
• How to plan to buy a new microcomputer system?

4
Electronic Data and Instructions

• A computer is an electronic machine and cannot
  understand human language.
• All data and instructions must be represented
  electronically in the computer.
• A conversion must occur from what we understand
  to what the computer can understand.
• The computer can only understand machine
  language, which is represented by a binary system.

5
Binary Systems

• A binary system is a two-state numbering system
  consisting of 0 and 1.
• Each 0 or 1 is called a bit (short for binary
  digit).
• 0 can be represented by electricity being off and
  1 by electricity being on.
• Bits are combined into groups of eight bits
  called bytes.
• Each byte represents one character.
• 8 bits 1 byte 1 character

6
Binary Coding Schemes

• These provide
• a language for computers to understand
• a means for computers to exchange data with other
  computers.

7
Binary Coding Schemes

• ASCII (American Standard Code for Information
  Interchange) the most widely used binary code
  for microcomputers.
• EBCDIC (Extended Binary Coded Decimal Interchange
  Code) developed by IBM and primarily used on
  large computers.
• UNICODE 16-bit code to support international
  languages like Chinese and Japanese.

8
How binary code is represented in

• circuitry it is either off (0) or on (1) inside
  the computer
• magnetized media magnetized spots are either
  absent (0) or present (1) on floppy or hard
  disks
• laser media laser pits are either absent (0) or
  present (1) on CDs.

9
Binary Coding Schemes
0100 0001
How the letter A is represented in ASCII code.
10
ASCII code
11
ASCII and EBCDIC Codes
12
System Board

• Allows I/O devices to communicate with the system
  unit.

13
System Board

• Main board or motherboard.
• Circuit board with sockets and chips.
• Every component of the system unit connects to
  it.
• All external devices need the system board to
  communicate with the computer.

14
Chip

• A chip consists of a circuit board etched on a
  small tiny postage-stamp-sized square of sandlike
  material called silicon.
• Also called a silicon chip, semiconductor, or
  integrated circuit.
• Chips are mounted on carrier packages, which are
  then plugged into sockets on the system board.

15
Microprocessor

• A microprocessor is a single chip that contains
  the central processing unit (CPU) of the
  computer.
• The CPU is the brains of the computer system.
• The CPU has two components,
• the control unit and
• the arithmetic-logic unit (ALU).

16
Control Unit

• It tells the rest of the computer system how to
  carry out program instructions.
• It directs the flow of electronic signals between
  memory and the arithmetic and logic unit.
• Directs signal flow between the CPU and input and
  output devices.

17
Arithmetic-Logic Unit

• The ALU performs
• arithmetic operations such as addition,
  subtraction, multiplication, and division
• logical operations such as comparing data to see
  if one is equal to (), less than (lt), or greater
  than (gt) another.

18
Microprocessor Chips

• The capacity of a microprocessor chip is
  expressed in word size.
• A word is the number of bits that can be accessed
  at one time by the CPU.
• Common word sizes are 16 bits (2 bytes), 32 bits
  (4 bytes), or 64 bits (8 bytes).

19
Microprocessor Chips

• The more bits in a word, the more powerful and
  faster the computer because it can move larger
  amounts a data at one time.
• Moving larger amounts of data at one time can
  increase the computers speed.
• Speed in processing data in a microcomputer is
  measured in microseconds (millionths of a second).

20
Microprocessor Chips

• CISC
• complex instruction set computer
• Pentium III and Pentium IV are most recent forms
• Includes AMD and Cyrix

21
Microprocessor Chips

• RISC
• Reduced Instruction Set Computer
• Fewer instructions, simpler and less costly
  design than CISC
• Motorolas PowerPC
• Compaq's Alpha
• Silicon Graphics' MIPS

22
Specialized processor chips Smart Cards

• Smart Cards use a tiny built-in microprocessor.
• Smart Cards are about the size of a credit card.
• Smart Cards can be used to hold specialized data
  such as health insurance information, frequent
  flier records, drivers license information, etc.

23
Memory

• Memory is a computer chip in a microcomputer that
  
• holds data for processing,
• instructions for processing the data, and
• information waiting to be output or sent to
  secondary storage.

24
Memory Three types

• RAM (Random Access Memory)
• ROM (Read Only Memory)
• CMOS (Complementary Metal-Oxide Semiconductor)

25
Memory
RAM programs and data
CMOS flexible start-up instructions
26

RAM

• Chips that hold the program and data that the CPU
  is presently processing.
• Temporary and volatile as soon as the
  microcomputer is turned off, everything in RAM is
  lost.
• Exception - flash RAM (very expensive, only used
  primarily in high-end portable computers)

27
Amount of RAM

• RAM must be large enough to hold software
  instructions for all programs that are running.
• RAM must be large enough to hold all data needed
  for processing.
• The more RAM (memory) a computer has, the more
  instructions and data it can hold at one time.

28
Memory Capacity
Megabyte (MB) 1 million bytes
Terabyte (TB) 1 trillion bytes
29
Virtual Memory

• Virtual Memory is the concept of dividing a large
  program into parts and storing the parts on a
  secondary device, such as a hard disk, during
  processing.
• Each part of the program is read into RAM only
  when needed.
• Most of todays operating systems support virtual
  memory.

30
Cache Memory a high speed holding area

• Cache Memory is a temporary holding area between
  the memory and the CPU.
• It is used to store the most frequently accessed
  information stored in RAM.
• Cache Memory is also known as RAM cache.

31
Cache Memory a high speed holding area

• The computer detects which information in RAM is
  most frequently used and copies that information
  into the cache.
• Not all computers have cache memory.
• Computers with cache memory are faster because
  the CPU can access data more quickly.

32
ROM (Read Only Memory)

• ROM are chips that have programs built into them
  at the factory.
• ROM chips are not volatile and cannot be changed
  by the user.
• ROM chips typically contain special instructions
  for computing operations.
• The CPU can read, or retrieve, the programs
  written on the ROM chip when needed.

33
ROM (Read Only Memory)

• The CPU cannot, however, write, encode, or change
  any information on a ROM chip.
• ROM chips are also known as firmware.
• ROM instructions usually contain instructions to
  boot up the computer, translate keyboard keys, or
  display characters on the screen.

34
CMOS (Complementary Metal-Oxide Semiconductor)

• CMOS are chips that are powered by a battery and
  do not lose its contents when the power is turned
  off.
• The contents of CMOS chips can be changed to
  reflect changes in the computer system.
• CMOS contains information that is required every
  time the computer is turned on.

35
CMOS

• CMOS contains such information as
• RAM size
• Keyboard type
• Mouse device type
• Monitor type
• Disk drive types

36
CMOS

• CMOS chips can be changed to reflect the changes
  if more memory or new hardware devices are added
  to the computer system.

37
The System Clock

• The system clock is a component that controls the
  speed of operations within a computer.
• Program instructions are processed in conjunction
  with system clock cycles.
• The system clock is measured in millionths of
  beats (cycles) per second.
• The system clock measurement is called its speed.
• The speed is expressed in megahertz (MHz).

38
Expansion Slots and Cards

• Expansion cards are circuit board devices that
  can be inserted into expansion slots in a
  computers motherboard to add expanded
  capabilities to computer operations.

39
Expansion Slots and Cards

• Other names plug-in boards, controller cards,
  adapter cards, or interface cards.
• On the side of each expansion card is an area
  called a port, which allows a cable to be
  connected from the expansion card to a device
  outside the system unit.
• Expansion slots provide an open architecture
  which allows users to add new devices to the
  system.

40
Expansion Slots and Cards

• Network Adapter Cards
• SCSI adapter
• Television boards
• PC/TV combo cards

41
Expansion Slots and Cards

• PC cards
• PCMCIA cards
• Sound Board
• Video Adapter Card
• CD-ROM card

42
Plug-and-Play

• A computer system needs to be reconfigured when
  an expansion board is added.
• Plug and play may eliminate reconfiguration
  tasks.
• Reconfiguration may require setting special
  switches on the expansion board and creating
  special configuration files.

43
Plug-and-Play

• Plug and play is a set of hardware and software
  standards recently developed by Intel, Microsoft,
  and others.
• With plug and play, operating systems, processing
  units, and expansion boards are able to configure
  themselves.
• Not all computers are plug and play, but most new
  computers are.

44
Bus Lines

• Data pathways that connect system components

45
Bus Lines
46
Bus Lines

• Data roadway for travelling bits
• More lanes, faster traffic 64 bit bus faster
  than a 32 bit

47
Ports and Cables

• Ports are connecting sockets
• Cables connect input and output devices to ports

48
Ports and Cables

• Four common ports
• Serial (mouse, keyboard, modem)
• Parallel (printer)
• USB (for several devices faster than serial and
  parallel ports)
• FireWire (the newest for high speed sprinters
  and video cameras faster than USB)

49
Cables
50
Major System Unit Components
System board Holds the various other
system components
Memory Holds programs and instructions
Expansion Connect to network and
other slots/boards system capabilities
Ports Connect outside devices to system unit