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1.
Computer Systems
Introduction to Personal Computer (PC) system
Computer system is made up of many parts called hardware. Hardware is controlled
by software – a set of instructions you send to your computer.
Computer System
Hardware
Software
Input
Device
System
Backing
Central
Output
Main
Applications
Software
Store
Processing Device
Memory
Software
Unit
The figure below illustrates how the hardware, the systems software and the
applications software are related:
Applications
Software
Systems
Software
Hardware
The figure below shows how the major hardware components are related:
2. Hardware
2.1 System Units
(a) Central Processing Unit (
)
CPU is the "brain" of the computer, which consists of:
i) Control Unit (
)
- it takes instructions from memory, interprets and causes the other
hardware elements to function.
ii) Arithmetic and Logic Unit (
)
- it performs the arithmetic operations (+, -, *, / ) and the logical
operations (AND, OR, NOT).
iii) Registers (
)
-
They are special temporary memory locations inside a CPU to store
instruction or data for certain purposes.
iv) Cache
- it is a high-speed memory that holds data which duplicate some data
stored in MM. When the data needed by the CPU are stored in cache,
the access time will be much smaller than fetching from MM.
(b) Main Memory (
)
i) Random Access Memory (
)
- temporary working space for computer to store program and data.
- everything in RAM will be cleared once the computer is turn off.
ii) Read Only Memory (
)
-
information in ROM is permanently recorded.
it stores system program.
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2.2 Peripheral Devices
(a) Input Devices
1) Keyboard – a typical input device for entering text and numbers.
2) Pointing devices
Mouse – It consists of a ball which touches the desk and rotates freely in
any direction as the mouse is moved around. Its movement is detected to
generate electrical signals which are transmitted to the computer.
Light pen – When a light pen is put against a certain spot on the screen, it
picks up a significant amount of light energy when the electron beam
inside the VDU is passing under the light pen. When this happens, a signal
will be sent to the computer which will then deduce the position of the
spot pointed to by the light pen.
Touch screen – Touch screen device is designed to receive input (e.g.
choose an option from a menu) when a position of the screen is touched by
the fingers of the user.
Digitizer – It consists of a graphic tablet and stylus (a pen or a mouse). A
graphic tablet is a flat rectangular slab consisting of a grid of sensor wires.
User draws on it with a stylus. When the tip of the stylus touches the tablet,
information about its position is sent to the computer.
3) Scanning devices
Image scanner – It operates like a photocopier. However, the image is
scanned into the computer in form of graphics instead of being printed on
paper.
Bar code scanner – Bar code is a set of black and white stripes used to
represent numbers. A bar code can represent a product code or a library
card number. Bar code scanner is used to scan bar code and sent to the
computer.
Magnetic Ink Character Reader – The input is human-readable
characters printed with magnetic ink. The characters are read by a
magnetic sensor. This technique is known as Magnetic Ink Character
Recognition (MICR). It is used in bank cheque processing.
Optical Character Reader – The input is human-readable characters.
Characters are read photo-electrically by light sensor. This technique is
called Optical Character Recognition (OCR). It is used to sort mails
automatically.
Optical Mark Reader – The Optical Mark Recognition (OMR) technique
can read pencil marks (by the conductivity or reflection of light) registered
in specified positions on a form.
Fax machine – A scanner + a printer + a communication device
4) Voice-input devices
The voice signal can be detected and recognized by voice recognition
device/program.
5) Chinese handwriting recognition device
Chinese hand writing can be entered through digitizer or mouse and the
character can be recognized by certain pattern recognition device/program.
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6) Video-capturing devices
Capture card is used for capturing video signals. For traditional video capture
card, it can capture analog video signal (video / S-video). For digital video
capture card (IEEE1394), it is for digital video camera.
b)
Output Devices
1)
2)
Visual Display Unit (VDU) – Information is displayed on the screen. Each
character is formed by a matrix of dots. Graphics can be displayed by
controlling the position of each dot on the screen. Large amount of data can be
displayed instantly.
Technologies of VDU: CRT (Cathode Ray Tube), LCD (Liquid Crystal
Display) and Plasma display.
Different resolution of VDU: 800x600 (VGA), 1024x768 (XGA)
Printer
Dot-matrix printer – A character is printed by striking a combination of pins
against the ribbon onto the paper. A pattern of dots in a rectangular array forms
a character. It can also produce graphics.
Ink-jet printer – In an ink-jet printer, electrically charged ink droplets are
produced and fired onto the proper position of the paper. Characters and
graphics are formed as dot-matrix form.
Laser printer – Uses the input data to control the scanning of laser beam onto
a charged cylinder. Carbon powder is then spread onto the charged cylinder and
transfer to a roll of paper. Finally it is made permanent by heat. Characters and
graphics are formed as dot-matrix form. Since the image is represented as a
series of minute dots, the print out is with “high quality”.
Others: Thermal printer, daisy wheel printer.
c)
3)
Plotter – Plotters can produce colourful graphic displays on paper. The
coloured pins move continuously on the paper under the control of the
computer.
4)
Voice-output device – Output can be in a sound format through a speaker.
Speech can also be outputted by using speech synthesizer.
Storage Devices / Backing Stores
It stores data permanently. Its capacity is large and it is cheaper than RAM.
Terms to be clarified on storage capacity:
1 bit
= 1 Binary digit
1 Byte =
1 K Byte =
1 M Byte =
1 G Byte =
1 T Byte =
1)
8 bits (1 character)
_______________ Byte
________________K Byte = ______________________ Byte
________________M Byte = ______________________ Byte
________________G Byte = _______________________Byte
Magnetic Disk
- A circular plastic / metallic sheet coated with magnetizable material.
- Data are stored as magnetized spots and non-magnetized spots on surface(s)
of the disk.
- Data are organized on the surfaces as a set of concentric circles called
______.
-
A track is divided into ____________. A sector holds a specified number
of bytes.
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Floppy disk – It is made of plastic material. It is removable with capacity
normally 1.44 MB. It is relatively low in accessing speed.
Hard disk – It is made of hard metal. It is a built-in storage with capacity from
20MB to xxx GB. It is relatively high in accessing speed.
2)
Magnetic Tape
- A strip of flexible polyester coated with magnetizable material is mounted
on a reel.
- Divided into 9 (or 7) parallel tracks. Data are recorded by a combination of
magnetic spots (a frame) vertically across with the width of a tape.
- A parity bit is added to each character for data validation.
- A tape is read / written by the read/write head of a magnetic tape unit.
- To access a location on a magnetic tape, all the preceding ones must be
accessed. This kind of access mode is called _________________________.
3)
Optical disk
- Optical disk is a glass of plastic disk coated with reflecting medium, on
which there are hole patterns representing information.
- When an optical disk is read, a very fine laser beam falls on the reflecting
surface. By detecting the variation of light intensity reflected from the
surface, the information stored in the disk can be obtained.
- The storage density of optical disk is high.
- 3 kinds of optical disks:
Read Only optical disk: ________________________________________
Write-Once-Read-Many (WORM) optical disk:_____________________
Read-Write optical disk:________________________________________
Capacity of different types of optical disk: CD (650MB), MD(140MB),
DVD(4.7GB)
4)
Flash memories
Flash memories are made of semi-conductors. They are small in size and
transferred in high speed. They are commonly used in digital cameras. They
will become a popular portable storage.
Examples: Compact flash, Smart media, Memory stick, SD card, MMC card,
XD card, Flash drive.
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3.
Software
Software is instruction or program to control the hardware. It can be divided into
two categories.
3.1 Systems software
Systems software provides a platform for users and applications software to
access the hardware. It helps us to communicate with the hardware.
(a) Operating System (OS)
An operating system is a collection of programs that control the operations
of a computer system. Generally it has the following functions:
 Memory management
 Input / Output control
 Error handling
 User Interface
(CLI: Command Line Interface, GUI: Graphical User Interface)
Examples: Windows, MacOS, UNIX, Linux
(b) Utility programs
Utility programs are supporting programs designed to perform specific
tasks to aid in achieving high levels of processing productivity. Examples:
1) File compression utility
2) Diagnostic utility
3) Disk scanner
4) Uninstaller
5) Disk defragmenter
6) Backup utility
7) Screen saver
8)
9)
Anti-virus program
Personal firewall
(c) Driver
Driver program or device driver is a small program designed to provide
information of a device to the operating system. Without certain device
driver, OS cannot control the corresponding device. OS includes common
device drivers such as those for keyboard, mouse and USB drive.
Examples: Printer driver, scanner driver etc.
3.2 Applications software
Applications software help us to solve our daily life problem. Examples:





(a)
Office software: Word processing, spreadsheet and presentation software.
Communication software: Web browser, e-mail client and FTP programs.
Graphical software: Painting software and drawing software.
Education software: CAI/CAL
Game: Adventure game, chess and RPG game.
Custom-made software /Tailor-made software
Custom-made software is written for specific application in specific
environment.
(b) Packaged software / Software package /Software suite
Packaged software is pre-written software which is widely used for
common applications in order to avoid unnecessary duplication of similar
programs by many users.