Chapter 5 The System Unit of a Computer System

1
Chapter 5 The 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

2
5.1 The System Unit (1)
Chapter 5 Computer System Unit

• A computer system consists of both hardware and
  software.
• Hardware
• actual machinery,
• e.g. the keyboard, mouse and monitor etc.
• Software
• programs or data.

3
5.1 The System Unit (2)
Chapter 5 Computer System Unit

• System Unit of a PC
• exists in the form of a metal case
• including
• motherboard, interface cards and storage devices
• Ports or Interface card
• Other devices, like keyboards, monitors and
  printers,
• are connected to the ports/interface cards
• through cables.
• Notebook computer houses almost all of its
  electronic components in the system unit

4
5.1 The System Unit (3)
Chapter 5 Computer System Unit

• Motherboard
• includes many different types of chips
• Chip (or integrated circuit, IC)
• semi-conducting material
• contain millions of transistors
• linked by conducting wires
• which are metallic paths printed on the
  motherboard.
• Providing computational and storage capability

5
5.2 Basic Computer System
Chapter 5 Computer System Unit

• 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 which connected to the
  motherboard are called Peripheral devices.

6
5.3 CPU (1)
Chapter 5 Computer System Unit

• Central Processing Unit (CPU)
• interprets and carries out the basic instructions
• operates a computer
• coordinates the tasks of other components of the
  computer

7
5.3 CPU (2)-Components
Chapter 5 Computer System Unit

• 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.

8
5.3 CPU (3)-Microprocessor
Chapter 5 Computer System Unit

• Large computers
• mainframes and supercomputers
• CPU is made up of many chips and requires
  multiple circuit boards.
• Personal Computer
• the CPU is usually contained on a single chip
  called microprocessor

9
5.3 CPU (4)-Speed
Chapter 5 Computer System Unit

• Clock speed
• indicates the capability of a CPU
• number of clock cycles or ticks per second
• Since an instruction requires a fixed number of
  clock cycles to complete, the higher is the clock
  speed, the faster is the CPU.
• 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 ticks in
  one second
• a 2.2 GHz Pentium 4 produces 2.2 billion ticks in
  one second.

10
5.4 Main memory (1)
Chapter 5 Computer System Unit

• Volatile
• Contents will be lost when the computer power is
  turned off
• Non-volatile
• Contents will be retained after the power is
  turned off

11
5.4 Main memory (2)
Chapter 5 Computer System Unit

• 1. Random Access Memory (RAM)
• hold instructions and data as computers are
  running
• volatile
• replaceable memory chips
• Loading
• copying data from secondary storage to RAM
• e.g. When powered on, some OS files are loaded
  from the hard disk onto RAM
• Saving a file
• copying data from RAM to non-volatile secondary
  storage

12
5.4 Main memory (3)
Chapter 5 Computer System Unit

• 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
• (when the computer is powered on or reset)
• called the Basic Input/Output System (BIOS)
• part of the system programs

13
5.4 Main memory (4)
Chapter 5 Computer System Unit

• Complementary Metal-Oxide Semiconductor (CMOS)
• Contents can be changed
• Non-volatile
• Stores configuration about a computer, including
• Capacity of the hard disk
• Types of existing ports, keyboard and monitor
• Current time and date
• CMOS does not store programs

14
5.4 Main memory (5) - Comparison
Chapter 5 Computer System Unit
15
5.4 Main memory (6) -Memory Size
Chapter 5 Computer System Unit

• Memory Size
• measured in byte
• 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
• For simplicity, 1024 is rounded down to 1000.
  Therefore, 1 MB equals approximately one million
  bytes and 1 GB approximates one billion bytes.

16
5.4 Main memory (7) - Data Access
Chapter 5 Computer System Unit

• Memory address
• Main memory is a series of locations
• Each of length 1 byte
• Each has a unique address, counting from zero
• In 1 K memory, address ranges from 0 to 1,023
• Since address is limited, the memory size is
  limited
• Largest memory size depends on the architecture
• Access is memory is called Direct Access
• since each byte has a unique address
• Data retrieve or store is efficiently
• Opposite to Sequential Access
• e.g. searching from a tape or finding from a
  word document

17
5.5 Buses in a computer (1)
Chapter 5 Computer System Unit

• Bus
• Channel for data transfer
• Allowing a series of electronic bits to transmit
  at the same time
• between
• A. (1) memory and (2) peripheral devices
• B. (1) memory and (2) CPU
• A bus consists of two parts
• Address bus
• Data bus
• When data is fetched from memory, the address is
  sent over address bus and the data is copied from
  the memory to data bus

18
5.5 Buses in a computer (2)
Chapter 5 Computer System Unit

• 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
19
5.5 Buses in a computer (3)
Chapter 5 Computer System Unit

• Bus Width
• The width of a channel
• Number of bits transmitted at one time
• e.g. a 32-bit bus can transmit 32 bits (four
  bytes) at a time
• Affects the overall performance of a computer

20
5.6 Ports and Interface cards (1)
Chapter 5 Computer System Unit

• Ports
• Built on the motherboard
• Interface between peripheral devices and memory
• Connect directly to Peripheral buses
• Interface cards
• Circuit board that connects a peripheral device
  to the motherboard
• Inserted into Interface slots which are built on
  the motherboard
• Connect directly to Peripheral buses

21
5.6 Ports and Interface cards (2)
Chapter 5 Computer System Unit
22
5.6 Ports and Interface cards (3)
Chapter 5 Computer System Unit