Title: Computer Operation Subject: Computer Studies EDD 5161 F Educational Communication & Technology

About the author … Name of student: Fok Yan Ming Student ID:

Introduction The target audience are form 4 students. This slide show will be presented as a lecture.

Computer Operation What can you find in a personal computer?

Input device Output device How about this case?

What can you find In my body ?

Central Processing Unit (CPU)  Control Unit (CU)  It coordinate machine activities.  Arithmetic and Logic Unit (ALU)  It performs data manipulation.  Memory Unit (This name is seldom used)  It accesses the main memory cells.

There are some components in each unit. Control UnitProgram Counter Instruction Register Instruction Decoder Arithmetic and Logic UnitAccumulator Status Register Logic Circuit Memory UnitMemory Data Register Memory Address Register Address Decoder

In Control Unit (CU)  Program counter (PC)  To hold the address of the next instruction.  Instruction register (IR)  To hold the instruction currently executed.  Instruction decoder  To decode the instruction.

Let’s see how the control unit works! Box 1 Box 2 Box 3 The Treasure Boxes Clean the board See the teacher Collect The forms Now the teacher give you three treasure boxes. Each box contain a command from the teacher. You cannot open the boxes or read the commands yourself. The monitor knows which box should be opened and the monitress reads the command inside the box.

Box 1 Box 2 Box 3 The Treasure Boxes Clean the board See the teacher Collect The forms Box 1 The monitor knows which box should be opened.

Box 1 Box 2 Box 3 The Treasure Boxes Clean the board See the teacher Collect The forms Box 1 The monitress reads the commands. Box 2 At the same time, the monitor prepares to show you the next box should be opened.

Box 1 Box 2 Box 3 The Treasure Boxes Clean the board See the teacher Collect The forms But you don’t know English! Oh! ?

Box 1 Box 2 Box 3 The Treasure Boxes Clean the board See the teacher Collect The forms 叫你擦黑板呀！ 哦，我明白啦！

Box 1 Box 2 Box 3 The Treasure Boxes Clean the board See the teacher Collect The forms The monitor plays the role of Program Counter. The monitress plays the role of Instruction register. The translator plays the role of Instruction decoder.

Interpretation Main Memory Inp A Sto B End :::::::: 001 Program Counter Inp A Instruction Register Program Decoder

In Arithmetic & Logic Unit (ALU)  Accumulator (ACC)  To hold the result or intermediate result of the operation temporarily.  Status register (SR)  To hold the status flag which show the status of the content in the accumulator.  Logic circuit  To perform arithmetic and logic operation.

Accumulator The accumulator acts as the note pad. You can jot down the intermediate result (or final result) of your calculation. For example, when evaluating ( )  (2.4 – 1.8) You better jot the result ( ) and (2.4 – 1.8) on the note pad, right?

Status Register It describes the current status of the accumulator. When 0 or 1 is assigned to the flags in status register, the status can be shown.

For example, 9 Accumulator Status Register odd integer positivezero -2

Interpretation In this example, we only have four flags. You may imagine that if we have many flags…. we can describe the content in the accumulator accurately

 Memory Data register (MDR)  To hold the data or instruction to be stored in or fetched from main memory.  Memory Address register (MAR)  To hold the address of the memory location to be accessed.  Address Decoder  To location the memory cell whose address is stored in MAR. In Memory Unit

In the previous example about control unit, the instruction seems to be accessed directly. Actually, we must access the main memory via the MAR and MDR. Now lets see an demonstration.

Main Memory Inp A Sto B End :::::: 001 Program Counter Inp A Instruction Register MAR MDR Address Decoder 001 Inp A

Instruction decoder IRPC CU Logic circuit SR ACC ALU Address decoder MAR Memory Unit MDR The Central Processing Unit Summary

This is the end. Click the button to exit.