Computer Operation What basic hardware components are inside a personal computer?

System unit Input devices CPU Main memory (RAM, ROM) Output devices Secondary storage

Arithmetic and logic unit Control unit Memory unit Input/ output unit CPU control bus data bus address bus Simple Model Computer block diagram

There are some components in each unit. Address Decoder Memory Address Register Memory Data RegisterMemory Unit Arithmetic and Logic Unit Control Unit Logic Circuit Status Register Accumulator Instruction Decoder Instruction Register Program Counter

Arithmetic and logic unit SRACC ALU  It performs arithmetic(i.e. mathematic) manipulation.  Accumulator (ACC)  To hold the final result or intermediate result of the operation temporarily.  Status register (SR)  To describe the status of the current content in the accumulator.  Logic circuit  To perform arithmetic and logic operation.

Accumulator The accumulator acts as the rough work sheet. You can write down the intermediate result or final result of your calculation. For example, when evaluating (4 + 2) + (8 – 3) You better write down the result on the rough work sheet!! Exercises

Status Register It describes the current status of the accumulator. These flags include the zero flag, carry flag, overflow flag, negative flag, etc.

For example, 9 Accumulator oddintegernegative zero

0 Accumulator oddintegernegative zero

-1.8 Accumulator oddintegernegative zero

Instruction decoder PC IR Control unit It directs all operations within the computer Instruction register (IR) To hold the current instructions Instruction decoder To interprets the current instruction Program counter (PC) To hold the address of the next instruction. Exercises

Let’s see how the control unit works! For example, you are a soldier. The General Mr. Chan gives you several confidential envelops. Each envelop contains only one command from the General.

The Commander A knows the order to open the envelop and the Commander B reads the command inside each envelop. You cannot open the envelops or read the commands yourself. The Messenger translate the command to you.

The Commander A knows which envelop should be opened first and give it to Commander B.

The Commander B reads the command. At the same time, the Commander A prepares to give Commander B the command of the next envelop.

However, you don’t know English!!!!! The Messenger translate the command to you. 叫你走佬呀 !!!! Then you know the command from the General Mr. Chan. 我知啦 !!!!

The Messenger plays the role of instruction decoder. The Commander B acts as Instruction register. The Commander A acts as Program Counter.

Control unit +1 PC IR Instruction decoder Main memory READ A 04 READ B READ A Data flow among the IR, PC, instruction decoder and main memory

main memory address decoder MDR MAR Memory Unit  Memory Address register (MAR)  To hold the addresses of the data or instructions to be accessed.  Memory Data register (MDR)  To hold the data or instructions to be written to or fetched(read) from main memory.  Address Decoder  To interpret the address held in the MAR.

Control unit +1 PC IR Instruction decoder Memory unit READ A 04 READ B 05  MAR MDR Address decoder Main memory 03 READ A 03 READ A Data flow among the IR, PC, instruction decoder, MAR, MDR, address decoder and main memory

Question 1 Work Harder Exercises Question 2 Question 3 Question 4 Question 5 Ans 1 Ans 2 Ans 4 Ans 3 Ans 5

Exercise One Exercises Which of the following registers is NOT in the control unit ? Instruction Register Program Counter Memory Data Register Accumulator Hint

Exercise One Which of the following registers is NOT in the control unit ? Instruction Register Program Counter Memory Data Register Accumulator Exercises

Exercise Two Decoder is a component of the Visual display unit. Main memory CU ALU Exercises Hint

Exercise Two Exercises Decoder is a component of the Visual display unit. Main memory CU ALU

Exercise Three Exercises What is the instruction register? The circuit required to decode the instruction The memory location of the next instruction to be executed The register to hold the address of the next instruction The register to hold the instruction to be executed Hint

Exercise Three Exercises What is the instruction register? The circuit required to decode the instruction The memory location of the next instruction to be executed The register to hold the address of the next instruction The register to hold the instruction to be executed

Exercise Four Exercises Which of the following about program counter is/are correct? (1) It holds the address of present instruction. (2) Its content changes automatically. (3) Its content cannot be altered by user. (1) only (2) and (3) only (1) and (3) only (2) only Hint

Exercise Four Exercises Which of the following about program counter is/are correct? (1) It holds the address of present instruction. (2) Its content changes automatically. (3) Its content cannot be altered by user. (1) only (2) and (3) only (1) and (3) only (2) only

Exercise Five Exercises Which of the following about accumulator is/are correct? (1) It is a general purpose register. (2) It is used to store the results temporary. (3) It is the register that the ALU acts on. (1) only (2) and (3) only (1) and (3) only (2) only Hint

Exercise Five Exercises Which of the following about accumulator is/are correct? (1) It is a general purpose register. (2) It is used to store the results temporary. (3) It is the register that the ALU acts on. (1) only (2) and (3) only (1) and (3) only (2) only

Exercises