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Chapter 11

The system unit of a computer system

The system unit of a computer system

Explain the functions of hardware within a computer system, namely input and output devices, the central processing unit, bus system and storage devices (both primary and secondary).
Explain the structure and functions of a central processing unit (CPU) and its components.
Outline the steps in the fetch-decode-execute cycle and store using a single processor, and describe the roles of and the interdependence among components, registers and buses in the machine cycle
Describe the functions and characteristics of Random Access Memory (RAM), Read Only Memory (ROM) and memory cache. Realise the relationship among the size of the memory, the memory address, word length and the performance of the computer.
Describe the features, advantages, disadvantages and applications of the input and output devices. Select and justify the use of appropriate devices for collecting and displaying information in a given context.
Describe the functional characteristics of storage devices in terms of random or sequential access, volatile or non-volatile, data transfer rate and storage capacity.
Outline the latest developments in computer systems including processor capabilities, primary memory technologies, secondary storage devices and data communications.


11.1 The components of a computer.
System unit (主機) contains main board (motherboard) with CPU and RAM, power supply, storage devices.
Peripherals: hardware devices connected to the system unit.

Practical 1
ALL instruction and data should be LOAD into Main memory before processing

11.2 Central processing unit

Main Specifications of a CPU
1. Number of cores.
2. Clock frequency
3. Word Length
The above three are directly related to the computation power. You can use this figures to compare computation power of CPU in the same family.
4. Cache memory size
Cache memory is a temporary storage area inside CPU. It reduce the needs to fetch instruction/data from Main memory.

Major Components of a CPU

ALU (Arithmetic and logic unit) 
performs arithmetic (numeric result) and 
logical operations.(True and false result, e.g. condition of IF statement)

CU (control unit) 
keeps tracks of the sequence of instructions being processed.
Control machine cycle
Control all IO operations

Accumulator: Store temporary result of calculation.

General purpose registers (AX, BX, CX, DX)

Control registers:
Instruction Register (IR)
Program counter (PC)
Memory Address Register (MAR)
Memory Data Register (MDR)
Status register (SR)

Refer to P.9-10 of textbook

System Bus
Data Bus
Address Bus
Control Bus

Example : Go to N203's cabinet to get a box of chalk.

Control : Get
Address: N203's cabinet
Data: a box of Chalk

11.3 Machine Cycle

Fetch - Decode - Execute

11.4 Measurement of CPU speed
Example 3,4  (P.15, 16)


11.5 Main memory

 volatileNon volatile 
 READ and WriteRead only 
 application program, data etcBootStrap program 
Use VM to demonstrate Bootstrap.

         erasable programmable ROM
         Electrical Erasable Programmable ROM (setting in BIOS)


P.20:The technology of Flash memory, SSD hard disk are similar to main memory. BUT it is NOT consider as main memory, it is SECONDARY storage.

P.21 Activity 2 (Already obsolete)

Latest Technology of CPU and Main memory
Study the latest CPU for Desktop http://www.intel.com

Should also notice the development of Smart phone, Notebook, Tablet PC.


In our new computer, we have 4 RAM slots. Each slot can support up to 8GB.

Now, we have installed 2 x 4GB. What is the advantage and disadvantages of using 2x4GB instead of 1x8GB?
Subpages (1): chp11_answer