Transcript 投影片 1 - 佛教沈香林紀念中學

P.1
1.1 Central processing unit(CPU)
1.2 Memory
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1.
2.
3.
4.
What is Central processing unit(CPU)?
What does CPU look like?
What does CPU contains?
Where does the microprocessor gets its
instructions?
5. What makes one microprocessor perform better
than another?
6. What do MHz and GHz have to do with computer
performance?
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1. What is Central processing
unit(CPU)?
Central processing unit (CPU)
accepts and executes
sequentially the instructions
stored in the main memory.
It is an integrated circuit
designed to process instructions.
It is the most important
component of a computer.
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2. What does CPU look like?
Looking inside a computer, you can usually identify the
microprocessor because it is the largest chip*1 on the
motherboard.
Depend on the brand and model, a microprocessor might be
housed on
1. SEC cartridge
2. Square PGA
*1
Chip : The term "chip", "computer chip" and "microchip" originated as technical jargon for
Integrated Circuit (IC), which is a super thin slice of semi-conducting material packed with
microscopic circuit elements such as wires, transistors, capacitors, logic gates and resistors.
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3. What does CPU contains?
The CPU contains the control unit (CU) , the arithmetic
and logic unit (ALU) and several registers.
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Control Unit (CU):
The function of the control unit (CU) is to direct all
operations occurring within the computer.
It is responsible for:
1. sending and receiving control signals to and from
peripheral devices
2. interpreting the instructions stored in main memory
3. regulating the timing of all operations performed
within the CPU
4. sequencing the instructions to be executed
5.controlling the flow of data between the CPU, main
memory and peripheral devices.
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The control unit contains an instruction register (IR)
instruction decoder*3 and a program counter (PC) *4
*2
, an
*2 Instruction Register : A register is a storage unit which has a specified storagecapacity. It
is used for temporary storage of instructions, data and addresses. An instruction
register(IR) is a register that holds the current instructions fetched from main memory.
*3 Instruction decoder : An instruction decoder is a logic circuit which interprets the current
instructions stored in the instruction register.
*4 program counter(PC) : A program counter(PC) is a register which holds the address of
the next instruction to be accessed after the current instruction has been fetched.
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Arithmetic and Logic Unit (ALU):
ALU performs arithmetic operations, such as addition,
subtraction, multiplication, division etc..
It also performs logical operations such as decision making.
For instance, comparing two numbers to see if they are
the same.
The ALU makes use of registers when performing these
operations.
They include an accumulator*5 and a status register*6
*5 Accumulator :An accumulator(ACC) is a register which temporarily holds the intermediate
or final result of arithmetic and logical operations.
*6 Status Register : A status regidter(SR) describes the status of the current contents of the
accumulator and holds a collection of bits.
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4. Where does the microprocessor
gets its instructions?
The CPU accepts and executes sequentially the
instructions stored in the main memory or computer
program.
The list of instructions that a microprocessor can perform
is called its instruction set.
These instructions are hard-wired into the processor's
circuits and include basic arithmetic and logical operations,
fetching data, and cleaning registers.
A computer can perform very complex tasks, but it does so
by performing a combination of simple tasks from its
instruction set.
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5. What makes one microprocessor
perform better than another?
The performance of a microprocessor is affects by several
factors, including clock speed, word size, cache size,
instruction set, and processing techniques.
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6. What do MHz and GHz have to do
with computer performance?
The speed specification that you see in a computer and indicate
the speed of the microprocessor clock-a timing device that sets
the pace for executing instructions. Most computer ads specify
the speed of a microprocessor in megahertz (MHz) or gigahertz
(GHz).Megahertz means a million cycles per second. Gigahertz
means a billion cycles per second. That means a computer with
a 1.3 GHz processor is faster than a computer with a 1 GHz
processor or a 933 Mhz processor.
A cycle is the smallest unit of time in a microprocessor's
universes. Every action that a processor performs is measured
by these cycles. It is important, however, to understand that the
clock speed is not equal to the number of instructions that a
processor can execute in one second. In many computers, some
instructions occur within one cycle, but other instructions might
require multiple cycles. Some processors can even execute
several instructions in a single clock cycle.
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1. What is Memory?
The memory includes :
1. RAM and 2. ROM.
The RAM holds instructions and data temporary while the
ROM holds system programs and data permanently.
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1.2.1 RAM
1. What is RAM?
2. What does RAM look like?
3. Why RAM so important?
4. How does RAM work?
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1. What is RAM?
Random access memory(RAM) is a temporary holding area
for data, application program instructions and the
operating system.
In a personal computer, RA is usually several chips or small
circuit boards that plug into the motherboard within the
computer's system unit.
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2. What does RAM look like?
RAM is usually configured as a series of DIPs soldered onto a small
circuit board called a DIMM (dual in-line memory module).
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3. Why RAM so important?
RAM is the "waiting room" for the computer's processor. It
holds raw data that is waiting to be processed, as well as
the program instructions for processing that data.
In addition, RAM holds the results of processing until they
can be stored more permanently on disk or tape.
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4. How does RAM work?
In RAM, microscopic electronic parts called capacitors hold
the bits that represent data. You can visualize the
capacitors as microscopic lights that can be turned on or
off. A charged capacitor is "turned on" and represents a
"1" bit. A discharged capacitors is "turned off" and
represents a "0" bit.
Each blank of capacitors holds eight bits(=one byte) of
data. A RAM address on each bank helps the computer
locate data, as needed, for processing.
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1.2.2 ROM
1. What is ROM?
2. How is ROM different from RAM?
3. Why does the computer need rom too?
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1. What is ROM?
Read-only memory(ROM) is a type of memory circuit that holds the
computer startup routine.
ROM is housed in a single integrated circuit - usually a fairly large,
caterpillar DIP package - which is plugged into the motherboard.
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2. How is ROM different from RAM?
Whereas RAM is temporary and volatile, ROM is permanent
and non-volatile.
ROM circuitry holds "hard-wired" instructions that remain
in place even when the computer power is turned off.The
instructions in ROM are permanent, and the only way to
change them to replace the ROM chip.
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3. Why does the computer need rom
too?
When you turn off your computer, all instructions will be
cleaned. It is empty and doesn't contain instructions for
the microprocessor to execute while you turn on your
computer again.
ROM contains a small set of instructions called the ROM
BIOS(basic input/output system) in the CMOS
memory(complementary metal oxide semiconductor
memory) which is a type of chip that requires very little
power to hold data. These instructions tell the computer
how to access the hard disk,the computer can understand
your input,display output,run software, and access your
data.
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2.1 Input devices
2.2 Output devices
2.3 Storage devices
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 Input devices accept input data and pass them
to the CPU unit to process.
 There are various input devices to fit different
tasks, for example
1. Keyboards ,
2. Pointing Devices ( i. Mouse, ii. touch screen,
iii. light pen, iv. digitizer ),
3. Scanning devices (i. image scanner, ii. fax
machine, iii. bar-code scanner, iv. magnetic ink
character recognition, v. optical character
recognition, vi. optical mark recognition ),
4. voice - input devices ,
5. Chinese hand writing recognition device
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1. Keyboards
 Keyboards are the most commonly used input devices.
User enter data by pressing the corresponding keys on
the keyboard.
 There are several types of cables connecting between
Keyboard and computer : 1.wires , 2. infrared(IR) , 3. FM
microwave , 4. Blue Tooth etc.
 There are 3 kinds of keyboard port : 1. AT , 2. PS/2 , 3.
USB
It is designed for the
purpose for saving
time and reducing
errors.
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2. Pointing Devices
 Pointing devices allow users to relocate the
pointer on the screen, and then select data or
a command.
Pointing Devices containing:
 i. Mouse,
 ii. touch screen,
 iii. light pen,
 iv. digitizer
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i.) Mouse
 A mouse is a kind of pointing device that allows a user to
control the mouse pointer.
 The most common type of mouse has a small ball on the
bottom and is attached with a cord to the system unit.The
ball senses the movement of the mouse and the mouse
pointer will move according to the movement of the
mouse.On top of the mouse, there are two or more
buttons. The user can perform an action such as selecting
an item by pressing the button.
 There are several types of cables connecting between
mouse and computer : 1.wires , 2. infrared(IR) , 3. FM
microwave , 4. Blue Tooth etc.
 There are 3 kinds of mouse port : 1. AT , 2. PS/2 , 3. USB
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ii.) touch screen
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A touch screen allows a user to enter data by touching the
touching the screen with a finger.It is faster than typing on
a keyboard or using a mouse.
However, it is not suitable for inputting a large amount of
data. A touch screen is commonly used in public services
such as information seeking.
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iii.) light pen
 A light pen is a device connected to a computer, that
when pointed at a computer display senses whether or
not the spot is illuminated. It then sends the information
to the computer.
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iv.) digitizer
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A digitizer can be used to trace or copy a drawing or a
photograph. The shape is then converted to digital signals
that are transmitted to the computer
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3. Scanning devices
 Scanning devices record image of text,
drawings or special symbols in their original
forms. The images are then converted to digital
data that can be processed by the computer.
Using scanning devices eliminates human
operation, thereby increasing efficiency and
reducing human error.
 Scanning devices containing :
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i.) image scanner
ii.) fax machine
iii.) bar-code scanner
iv.)magnetic ink character recognition
v.) optical character recognition
vi.) optical mark recognition
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i.) image scanner
 An image scanner captures
images or text onto the
computer.
 The scanner will digitizes the
input data so that they can be
processed by the computer.
Once the image or text are
digitized, they can be modified
and merges with other text or
images.
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ii.) fax machine
 Fax machine communications system for the electrical
transmission of printed material, photographs, or
drawings. Facsimile transmission is accomplished by radio,
telephone, or undersea cable.
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iii.) bar-code scanner
 A bar code scanner is a photoelectric scanner that reads
the bar codes printer on product containers.

A bar code scanner consists of a set of vertical lines with
different widths. The bar codes canner identified a bar code by
the reflected light pattern from the bar code lines. The most
familiar bar code system is the Universal Product Code(UPC).
The UPC can be translated into a ten-digit number that
identifies a product, You can easily find a bar code scanner at a
point-of-sale terminal in a supermarket.
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iv.) magnetic ink character recognition
 A character recognition system using special ink
and characters which can be magnetised and
read automatically.
 MICR is used almost exclusively in the banking
industry where it is used to print details on
cheques to enable automatic processing.
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v.) optical character recognition
 An optical character reader(OCR) can recognise
characters with special typefaces.
 An OCR uses a light source to read the shape
of a character and converts the image into
digital data. The OCR then compares the
pattern read with a predefined pattern in
memory. The read character is assumed to be
the character whose stored pattern most
closely matches the read pattern. The OCR is
commonly used in department stores to read
retail price tags.
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vi.) optical mark recognition
 A technique that enables marks made in
predetermined positions on computer-input
forms to be detected optically and input to a
computer.
 An optical mark reader shines a light beam
onto the input document and is able to detect
the marks because less light is reflected back
from them than from the paler, unmarked
paper.
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4. voice-input devices
 Users can enter data or give commands to the computer
with spoken words through voice - input devices.
 Through a microphone and digitise them, so that they
can be processed by the computer. The command may be
performing a specific action such as saving a document
or operating industrial machines.
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5. Chinese hand writing
recognition device
 Users write a character
with a special device
such as a special pen or
writing pad.
 The system recognizes
the shape of the written
character and matches it
to the most similar
character. Then a list of
these characters is
shown for selection.
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 Output devices are used to present the
information to users.
 There are various output devices to fit different
tasks, for example,
 1. Visual display unit
 2. Printers (i. Laser Printers, ii. Ink-jet
Printers, iii. Dot-matrix Printers )
 3. Plotters
 4. Voice-output device
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1. Visual display unit
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Basically, a VDU is a monitor which looks like a television. It can
be used to display images such as text, graphics and even video
films or animation.
A pixel is the smallest unit on the VDU that can be turned on and
off or made different shades. The most important features of a
monitor are its screen size, number of maximum displayable
colours and resolution. the resolution of the image on the VDU
depends on the density of the pixels, that is, the number of rows
and columns of pixels. There are two kinds of VDUs.
cathode-ray tube (CRT) and liquid crystal display (LCD) monitors.
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2. Printers
 The image output on a monitor are often referred
to as soft copy, while that on paper is called hard
copy.
 Printers are commonly used output devices that output
image on paper. In general, there are two types of
printers: impact printers and nonimpact printers. Impact
printers transfer characters onto paper by striking the
paper, ribbon and character together. Nonimpact printers
output images on paper without physically touching
thepaper. Nowadays, only one type of impact printers,
dot-matrix printers are used.

Printers are containing :
 i.) Laser Printers
 ii.) Ink-jet Printers
 iii.) Dot-matrix Printers
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i.) Laser Printers
 A laser printer uses laser beams to create images. Laser
printers can produce high quality images at high speed.
They are commonly used to produce high-quality hard
copies. Laser printers can print on paper and
transparencies.
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ii.) Ink-jet Printers
 An ink-jet printer sprays droplets of ink onto the paper or
transparences through nozzles to form characters and
images. Ink-jet printers are reliable and quiet. They are
suitable for printing graphics.
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iii.) Dot-matrix Printers
 A dot-matrix printer prints images using a series of wire
pins on a print head. A small dot is printed by striking a
wire pin again an inked ribbon. These small dots form
different characters and images.
 Dot matrix printers are noisy, and the printing speed and
output quality are fair. However, many organizations use
dot-matrix printers to print documents with a large amount
of data, such as, bills and invoices.
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3. Plotters
 Plotters are used to produce high-quality line
drawing such as maps, charts, building plans and
circuit diagrams.
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They can produce high-quality multicolour documents and
also documents that are larger in size than most printers can
handle. There are three main types of plotters: pen, ink-jet
and electrostatic plotter.
Plotters create plots by moving a pen or pencil over drafting
paper. Ink-jet plotters create line drawings and solid-colour
output by spraying droplets of ink onto paper. Lastly,
electrostatic plotters use electrostatic charges to create
images made up of tiny dots on specially treated paper.
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4. Voice-output device
 Instead of reading the soft copy and hard copy, users can
hear the information over speakers, headphones,
telephones, voice dictionaries and so on.
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 Storage devices is storage separate from the CPU.
It can hold data and programs permanently for
future use.
 It is necessary because main memory can be used
only temporarily, and users may want to store the
data they have used or the information they have
obtained from processing. Furthermore, main
memory is limited in size, while storage can store
as much data as necessary.
 There are including :
 1. Floppy disk,
 2. hard disk,
 3. magnetic tape
 4. optical disk
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1. Floppy disk
 A floppy disk, often called diskette, is
a flat, circular piece of plastic that
rotates within a jacket. The plastic is
coated with a metal oxide film.
 Data and programs can be stored as
magnetic spots on the film. It is 3.5inch and provides 1.44 MB storage.
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2. Hard Disk
 A Hard disk consists one or more metallic platters.
Each side of the platters is coated with a metal oxide
film, and data can be stored as magnetic spots on the
film.
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The mechanism for reading or
writing data on a hard disk is
similar to that of a floppy disk.
However, if the hard disk consists
of several metallic platters, the
drive has several access arms
which move several read-write
heads in and out between the hard
disks.
Each access arm has two readwrite heads. One reads the disk
surface above it while the other
reads the disk surface below it. To
read or write on a particular track
of the hard disk, all the access
arms move in and out together,
and all the platters rotate at the
same time. However, only one of
the read-write heads is used at
each moment. It can be shown that
the access mode is direct access.
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3. Magnetic tape
Magnetic tape is a thin ribbon of plastic with magnetic coating
on one side.
 Magnetic tape is the cheapest secondary
storage medium, and is suitable for
storing a large amount of data.
 Data are recorded on or retrieved from
the tape sequentially. That is, the access
mode is sequential access. Magnetic tape
is seldom used in personal computers.
However, it is the primary means of
backup for minicomputers and
mainframes. The two common types of
magnetic tape are cartridge and reel-toreel.
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4. Optical disk
 Optical disks are hard plastic disks. Information is stored
by using a high-power laser to burn tiny holes on the
surface of the disk.
 A low-power laser reads the disk by reflecting light off the
disk surface. The reflected light is converted into bit
patterns that the computer can process. Hence, the access
mode is direct access. The storage capacity of optical disks
is amorous and much larger than that of floppy disks.
However, most optical disk cannot be modified by users.
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3.1
Modem
3.2
Network devices
3.3 Local area network
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Networks :
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Nowadays, computers are recognized as important
communication devices. By using computers, communication
between different places all over the world is possible;
information available on other computers can be accessed.
Some organizations, such as banks, airlines, hotels and
department stores, run a number of computer systems which
are linked up together to form a network. They can share
resources and information through the network.
A computer network is a system in which a set of computers
and other communication facilities are connected to each
other.
Networks allow users to
 1. communicate,
 2. share hardware, software and information.
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Modems are used to modulate digital signals to analog signals and demodulate
analog signals to digital signals so that the signals can be transmitted via telephone
lines.
Computer can communicate via telephone lines. However, only analog signals can
pass through telephone lines while data sent out from computers are in the form of
digital signals. To make the communication possible, modems are commonly used.
The modems can convert digital signals to analog signals. This process is called
modulation.
When computers receive data, modems can be used to convert analog signals to
digital signals. This process is called demodulation.
The term modem is used simply because it performs modulation and demodulation.
Note that a modem is needed to both the sending and receiving ends of the
telephone line.
An outside a computer (external modem) or inside the system unit (internal modem).
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Each device that is connect to a network is referred to as node.
Many network nodes are computers-some of them busily serve out
information, and others simply request information.
Behind the scenes, several network devices handle specialized
network tasks.
Network devices including :
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1. Communications channel
2. Modem
3. Network interface card
4. Server
5. Host
6. Hub
7. Router
8. Gateway
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1. Communications channel
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Computers use a variety of links to carry data, the
most common being :
1. Twisted-pair cable with RJ-45 Plug
 consist of a pair of twisted copper wires and
used for telephone lines. Twisted pair cables
typically terminate with plastic RJ-11 plugs for
telephones or RJ-45 plugs for computer
networks.
2. Coaxial cable with BNC connector
 a better quality communication channel
compared with twisted-pair wires. They can be
laid underground or underwater.
3. Fiber-optic cable with Fiber-optic Plug
 are smooth, hair-thin strands of glass. They
conduct light with high efficiency.
4. Microwaves
 electromagnetic waves which can be used to
provide high speed transmission of data.
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5. Radio waves
 Electromagnetic radiation with wavelengths of
300 millimeters or longer (even up to several
kilometers). Radiation of this type is used to
broadcast radio and television signals, and
has frequencies up to thousands of
megahertz (or one gigahertz).
6. Satellites
 man-made equipment that orbits around the
earth or the moon to transmit of data in long
distance.
7. Infrared light
 electromagnetic radiation with wavelengths
longer than visible light but shorter than radio
waves
 carry data signals but only for short distance
and with a clear line of sight.
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2. Modem
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Modem is a devices that converts the signals from a
computer into signals that can travel over a wide area
network, such as the telephone system or the internet.
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3. Network interface card
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Network interface card is a small circuit board that converts the
signals from a computer into signals that can travel over a local are
network. e.g. LAN card
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4. Server
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Server often refers to ant computer on a local area network or the Internet
that contains the software to manage and process files for other network
nodes.
The term "server" can also refer to the software that provides a network
service. E-mail servers, communications servers, file servers, and Web
serves are some of the most common servers on today's networks.
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5. Host
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Host usually refers to any computer that provides
services to network users.
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6. Hub
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A hub is a device that connects several nodes of a local area
network.
All of the devices that attach to a hub are part of the same local
are network.
Multiple hubs can be linked together to expand a local area
network.
To connect more than one local area network, or to connect a
local area network to the Internet, requires an additional device,
such as a router or a gateway.
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7. Router
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Router is a device that connected to at least two networks-sort of
like a spider sitting in the middle of a Web. Routers make decisions
about the best route for data, based on the data's destination and
the state of the available network links.
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8. Gateway
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Gateway is a device that performs functions similar to a
router. Both routers and gateways can be incorporated
on local area networks or the Internet.
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A Local area network (LAN) is a data communications
network that typically connects personal computers
within a very limits geographical area-usually a single
building.
The servers allow users to share resources and
information via LAN.
The main advantage of a LAN is that multiple users can
share a limited number of resources.
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4.1
Operating system
4.2 Utility programs
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4. System software
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System programs refer to programs that contol the
operation of computer equipment. For example, starting
up a computer, sorting and retrieving files, reading,
storing and executing application programs. In fact, such
operation is managed by the operating system.
Software consists of computer programs, support
modules, and data modules that work together to provide
a computer with the instructions and data necessary for
carrying out a specific type of task, such as document
production, video editing, or Web browsing.
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The operating system (OS) is a collection of system
programs for controlling the resources of a computer
system and providing an interface between the computer
and the users.
The operating system performs its tasks without
intervention and the users are usually unaaware that the
operating system assists them in different ways.
However, if there is no operating system, a computer is
totally useless.
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Function of an operating system :
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1. Supervise programs
2. Communicate with users
3. Provide utilities
4. Optimize the use of resources
5. Keep a log of all programs
6. Maintain security
7. Handle errors
Different operating systems on computer :
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1. Windows
2. MAS OS
3. LINUX
4. UNIX
5. DOS
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a program designed for general support of the processes
of a computer
a computer system provides utility programs to perform
the tasks needed by most users
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P.72
5.1 Custom-made software
5.2 Packaged software
Created by Lo Wing Tat
P.73
5. Application software
 Applications programs refer to programs designed for
users to perform specific tasks. For example, Document
Production software, Spreadsheet software, Graphics
software, etc.
 allow users to write documents, perform calculations,
generate spreadsheets and create graphics.
Created by Lo Wing Tat
P.74
 A custom-made software is a set of detailed , step-bystep instructions that tell a computer to solve a problem
or carry out a task.
 Computers operate according to lists of instructions or
programs.
 These programs are normally written in some forms of
computer programming language which is an artificial
language designed to generate or to express programs.
 The following are some High level languages to write
software :
 1. BASIC
 2. C language
 3. Pascal
 4. HTML
Created by Lo Wing Tat
P.75
 Packaged software refer to programs designed for users
to perform specific tasks.
 The following are some Packaged software :
 1. Word Processing Software Package
 A word processing software package enable users to
produce and modify high quality documents that consists
mainly of text.
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P.76
 2. Spreadsheet software Package
 A spreadsheet software package can manipulate
worksheets which present mainly numeric data in a table
format.
 3. Database Management Package
 A Database Management Package allows users to create,
retrieve and modify database.
 4. Graphics Software Package
 A Graphics Software Package can manipulate drawings
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P.77
Special:
1. Colourful
2. Many Pictures
3. Hyperlink
4. Button
5. Different master slice
Created by Lo Wing Tat
P.78
P.79