Chapter 5 Chapter 5 The System Unit of a Computer SystemThe System Unit of a Computer System

5.1 System Unit 88

5.2 Basic Computer System 90

5.3 Central Processing Unit 91

5.4 Main Memory 93

5.5 Computer Bus System 97

5.6 Port and Interface 99

5.15.1 The System UnitThe System Unit (2) (2)

System Unit of a PC (p.89) motherboard, interface cards and

storage devices Ports or Interface card

Other devices, like keyboards, monitors and printers,

are connected to the ports/interface cardsthrough cables.

Notebook computer houses almost all of its electronic components in the system unit

Chapter 5 Computer System Unit

5.25.2 Basic Computer SystemBasic Computer System A basic computer system consists of the following

hardware components: 1. Central Processing Unit (CPU) 2. Main memory 3. Input devices 4. Output devices 5. Secondary storage 6. Communication devices

For PC: The CPU and Memory are plugged on the motherboard. Those devices Those devices

which connected to the motherboard are called Peripheral devices.which connected to the motherboard are called Peripheral devices.

Chapter 5 Computer System Unit

The Components of a ComputerThe Components of a Computer

Peripherals (devices) items attached to system unit

Input Input

Input

Input

Output

Output

Output

Communication

5.3 5.3 CPUCPU (2)- (2)-ComponentsComponents

1. Control Unit (CU) controls the overall operations interprets program and sets off action controls peripheral devices.

2. Arithmetic and Logic Unit (ALU) carries out computational jobs, including

calculation, comparison and decision.

Chapter 5 Computer System Unit

Do Q. 3 on p. 102

ALU

How ALU and Control Unit work?

Main Memory

add two numbers

10 7 Control Unit

interpret instructions

perform operations

10 + 7 = 17

Retrieve an instruction

Tell ALU how to perform an operation

3. Registers high-speed storage locations temporarily hold data and instructions during

processing e.g. cache memory in CPU/ video accelerating

card/ hard disk; buffer in printer etc.

5.3 5.3 CPU (4)-SpeedCPU (4)-Speed

Clock speed number of clock cycles or ticks per second each instruction required a certain number of ticks to

complete. measured in hertz (Hz)

Mega (M) is a prefix representing one million (106). Giga (G) represents one billion (109).

For example, a 800 MHz PowerPC produces ~800 million clock cycles in one

second a 2.2 GHz Pentium 4 produces 2.2 ~billion clock cycles in one

second.

Chapter 5 Computer System Unit

5.45.4 Main memory Main memory (2)(2)

1. Random Access Memory (RAM) p.93 hold instructions and data as computers are running volatile

Chapter 5 Computer System Unit

CPU RAM Hard Diskloading

saving

5.45.4 Main memory Main memory (3)(3)

2. Read only memory (ROM) Store instructions and data permanently Non-volatile Contents can be read but cannot be changed also called Firmware

software (program) is stored in a chip instead of disc.

ROM chip may store programs for booting called the Basic Input/Output System (BIOS)Basic Input/Output System (BIOS)

Chapter 5 Computer System Unit

5.45.4 Main memory Main memory (5) - (5) - ComparisonComparison

Chapter 5 Computer System Unit

RAM ROM CMOS

Permanence volatile non-volatile non-volatile

Flexibility read and write read only read and write

Type ofinformation

data andinstructions being

processed

system program anddata

configuration data

Size largest small smallest

Upgradable yes; memory sizecan be increased

no no

5.45.4 Main memory Main memory (6) -(6) -Memory SizeMemory Size

Memory Size measured in byte (Ch. 2) exists in multiples of 1,024 bytes (kB) 1 kB = 1,024 bytes 1 Megabyte (MB) = 1,024 x 1,024 bytes 1 Gigabyte (GB) = 1,024 x 1,024 x 1,024 bytes

Chapter 5 Computer System Unit

5.45.4 Main memory Main memory (7) - (7) - DataData Access Access

Access mode of memory data is Direct Accesssince each byte has a unique addressData retrieve or store is efficiently

Opposite to Sequential Access e.g. searching from a tapesearching from a tape or finding from a word document

Chapter 5 Computer System Unit

5.5 5.5 Buses in a computerBuses in a computer (1) (1)

Bus Channel/wire for data transfer between

A. (1) memory and (2) peripheral devicesB. (1) memory and (2) CPU

A bus consists of threethree parts: Control bus Address bus Data bus

Chapter 5 Computer System Unit

Data bus transfer actual data

Address bus transfer information about the location of data

Control bus indicate the direction of data transfer coordinate the timing of events during the transfer

5.5 5.5 Buses in a computerBuses in a computer (2) (2)

Two basic types of bus: System bus (or processor bus)

channel between the CPU and

the main memory.

Peripheral buses channels between the main memory

and other devices,

Peripheral bus

Chapter 5 Computer System Unit

1. ISA bus

2. PCI bus

3. SCSI bus

4. USB

5. AGP bus

5.5 5.5 Buses in a computerBuses in a computer (3) (3)

Bus Width Number of bits (amount of data) transmitted at one

time Affects the overall performance of a computer

Chapter 5 Computer System Unit

5.6 5.6 Ports and Interface cardsPorts and Interface cards (1) (1)

Ports Connect motherboard (RAM) to Peripheral buses

/devices Interface cards

Inserted into Interface slots on the motherboard to connect the Peripheral buses (increases the number of ports of the system unit).

Chapter 5 Computer System Unit

5.6 5.6 Ports and Interface cardsPorts and Interface cards (2) (2)

Chapter 5 Computer System Unit

Port Name Peripheral devices

1. Keyboard and mouse port Keyboard, mouse

2. Serial port Mouse, modem, graphic tablet

3. Parallel port Printer

4. SCSI port Fast devices, e.g. hard disk

5. USB port large range of devices

6. 1394 port DV camera

7. IrDA port (Infrared Data

Association) Wireless devices

8. PC card port (for notebook

computers only)

PC cards, e.g. Network interface card,

hard disk, sound cards, radio

transceiver etc.

TaskTask

Read more catalogue of Computer System (PC + Notebook)

Try to understand the type and function of each part.

Best Computer Ltd.

CPU 4.2 GHz

RAM 2 GB

ROM 2 MB

Hard disk 160 GB

DVD drive 48X / 24X / 12X

Expansion slot 4 PCI

Sound card On-board

Network card Built-in Ethernet adaptor

Wi-Fi 802.11a/g built-in wireless card and antenna

Operating System Magic 300