Module 2: Computer System
P.1
CUHK FAA Thomas Cheung Secondary School
S.6 AS Level Computer Applications
Module 2: Computer System
Name : _______________________
Class : _____
Class No. : ___
Date : _____________
Section 1 : The System Unit of a Computer System
1. Introduction
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2.
A computer system consists of both hardware and software.
The system unit of a desktop personal computer exists motherboard(底板), interface cards(介
面卡) and storage devices.
The motherboard in the system unit includes many different types of chips. A chip or
integrated circuit (IC)合成電路 is a small piece of semi-conducting material that contain
millions of transistors. They are linked by conducting wires which are metallic paths printed
on the motherboard.
Other devices, like keyboards, monitors and printers, are connected to the ports or interface
cards of the system unit through cables.
Basic Computer System
2.1 A basic computer system consists of the following hardware components:
Item
Motherboard :
Peripheral devices
(周邊設備):
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Components
Central processing unit (CPU)
Main memory
Input devices
Output devices
Secondary storage
Communication devices
2.2 Interrelationship between various hardware components
Central Processing
Unit (CPU)
Input devices
Main Memory
Secondary storage
3.
Output devices
Communication
devices
Central Processing Unit (CPU)
The CPU interprets and carries out the basic instructions that operate a computer.
Central Processing Unit (CPU)
Control
Unit
Input device
Secondary
storage
Main memory
ALU
Control signal
Output devices
Inter-connection
n
Communication
devices
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3.1 Components of the CPU
The CPU consists of 2 major components:
1. Control Unit (CU)
 Controls the overall operations of the computer.
 Interprets an instructs from a program and set off appropriate action.
 Directs and controls the operations of the peripheral.
2. Arithmetic and Logic Unit (ALU)
 Carries out computational jobs, including calculation, comparison and decision.
3.2 Microprocessor
The CPU in a personal computer is the microprocessor.
Question :
1. Clock speed: Higher is better?
3.3 Speed of CPU
 The capability of a CPU is indicated by the clock speed, which is the number of clock cycle.
 Because an instruction requires a fixed number of clock cycles to complete, the higher is the
clock speed, the faster is the CPU.
 Clock speed is measured in hertz(Hz).
1 Mega = 1 M = 106
1 Gaga = 1 G = 109
Section 2 : Main Memory
1.
Introduction
Besides the microprocessor, main memory (or memory) is another important component found
on the motherboard. The main memory stores data and instructions(指令).There are 3 types
memory: Random Access Memory (RAM), Read Only Memory (ROM) and (CMOS).
2.
Types of memory
There are 3 types of memory: RAM, ROM and CMOS
*Volatile
RAM
Main memory
*Non-volatile
ROM
CMOS
RAM, ROM and CMOS
*Memory is classified into volatile and non-volatile.
Volatile : The contents of the volatile memory will be lost when the computer power is turned off.
Non-volatile : The contents of the non-volatile memory will retain after the power is turned off.
2.1 Random Access Memory (RAM)
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RAM stands for Random Access Memory.
A location to hold the necessary instructions and data as long as the computer is running.
It is volatile. Data stored in the RAM are lost when the power is turned off. Therefore, data
needed for future use should be saved.
Saving a file means copying data from RAM to the non-volatile secondary storage.
Loading meaning copying data from secondary storage to RAM.
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Module 2: Computer System
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2.2 Read Only Memory (ROM)
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ROM stands for Read Only Memory.
Store the sequence of instructions that the computer follows in the booting process(when the
computer is power on or reset). This particular sequence of instructions is called the basic
input/output system(BIOS), which is part of the system programs.
The contents in ROM can be read but they cannot be changed.
ROM is also called firmware, which means that the software (program) is stored in a chip
instead of disc.
2.3 Complementary Metal-Oxide Semiconductor memory (CMOS)
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3.
Another type of memory chip on the motherboard is Complementary Metal-Oxide
Semiconductor memory (CMOS).
Stores the configuration information about a computer.
Includes information like the capacity of the hard disk; the types of existing ports, keyboard
and monitor; the current time and date. However, CMOS doesn’t store program.
Unlike ROM, the computer can change the information in CMOS.
Unlike RAM, CMOS is non-volatile. The contents in CMOS can be retained after the
computer is power off.
Comparison between RAM, ROM and CMOS
RAM
Permanence
Flexibility
Type of
information
Size
Upgradeable
4.
ROM
CMOS
Non-volatile
Non-volatile
Read only
Read and write
System program and data Configuration data
Volatile
Read and write
Data and instructions
being processed
Largest
small
Yes; memory size can be no
increased
Smallest
no
Memory Size
1 Byte = 8 bits
1 KiloByte = 1 KB = 1024 Bytes
1 MegaByte = 1 MB = 1024 x 1024 Bytes = 106 Bytes
1 GigaByte = 1 GB = 1024 x 1024 x 1024 Bytes = 109 Bytes
Term
KiloByte
MegaByte
GigaByte
Abbreviation
KB
MB
GB
Exact memory size (bytes)
1024
1024 x 1024 (106)
1024 x 1024 x 1024 (109)
Question :
1. 128 KB = _______________ Bytes
2. 5 MB = _________ KB
3. 3 GB = __________ MB
5.
Access of Data in Memory
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The main memory can be thought of as a series of locations each of length one byte.
Each location has a unique address, counting from zero upward. The address is called
memory address.
For example, for a computer with a memory size of 1 K, the memory address ranges from 0
to 1,023.
Since the size of address is limited, the memory size is also limited. The largest memory size
depends on the architecture of a computer.
Memory size = 2 no. of address bus
For example, for a computer with 32 bits address bus, the memory size = 2 32 =__________
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Module 2: Computer System
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6. Buses in a computer
6.1 What is a bus?
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The CPU gets data from and stores data onto the memory. A channel links between the CPU
and the memory. Similar channels exist between the memory and the peripheral devices.
Each channel, called a bus, allows a serried of electronic bits to transmit at the same time.
A bus consists of 3 parts : address bus, data bus and control bus.
Address bus carries address of memory location.
Data bus carries data contents.
Control bus carries control signal.
6.2 Types of bus
 There ate 2 basic types of bus : system bus (or processor bus) and peripheral bus.
 System bus transfer data between memory and CPU.
 Peripheral bus transfers data between memory and peripherals.
CPU
System bus
Peripheral device
(Keyboard)
Peripheral device
(Monitor)
Main
memory
Peripheral device
(Hard disk)
Peripheral buses
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Examples of peripheral buses in a IBM-compatible PC are shown below:
Bus
Full Name
ISA bus
Industry Standard Architecture bus
PCI bus
Peripheral Component Interconnect bus
SCSI bus
Small Computer System Interface bus
USB
Universal Serial Bus
AGP bus
Accelerated Graphic Port bus
CPU
System bus
Peripheral bu
Hard disk
Main memory
Keyboard, mouse
USB device
(web cam)
AGP video card
6.3 Ports and Interface Cards
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A port is build on the motherboard and forms the interface between peripheral devices and
the memory or CPU.
An interface card is a circuit board that connects a peripheral device to the motherboard or a
computer.
Interface slots, build on the motherboard, allow interface cards to be inserted.
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Module 2: Computer System
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Port Name
Peripheral devices
Keyboard and mouse port (PS2 or serial port) Keyboard, mouse
Serial port
Mouse, graphic tablet
Parallel port
Printer
SCSI port
Fast devices, e.g. hard disk
USB port
Printer, scanner
1394 port
DV camera
Common ports and their corresponding peripheral devices
Card Name
Network Interface Card (NIC)
AGP video card
Sound Card
Modem Card
Peripheral devices
Switch or hubs of LAN or Internet
Visual Display Unit (VDU)
Microphone, speaker
Telephone network
Interface cards corresponding to their peripheral devices
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