1 - Processor Components

Question 1

What does CPU do

Answer 1

executes instructions and processes data by following fetch-decode-execute cycle

Question 2

3 functions of CU (Control Unit)

Answer 2

• Controls and coordinates the activities of CPU
• Directs the flow of data between the CPU and other devices
• Decodes instructions in FDE cycle

Question 3

What is a bus

Answer 3

Set of parallel wires connecting two or more components of a computer

Question 4

What is system bus made up of

Answer 4

address bus, data bus and control bus

Question 5

What does system bus do

Answer 5

Connect CPU to main memory

Question 6

Address bus

Answer 6

• sends memory address that processor needs to access from CPU to RAM
• Unidirectional: CPU -> RAM

Question 7

control bus

Answer 7

sends control signals from the control unit to coordinate use of address and data bus, ensuring it doesn’t lead to conflict
- Bi-directional

Question 8

Data bus

Answer 8

• Carries data and instructions between processor and memory

- Bi-directional

Question 9

ALU

Answer 9

performs arithmetic (e.g add/subtract) and logical (e.g AND, OR, NOT) operations

Question 10

Accumulator

Answer 10

a register that temporarily stores intermediate results from ALU until they’re written to memory

Question 11

Registers

Answer 11

Registers are small, very fast memory cells within the processor that temporarily store data

Question 12

PC

Answer 12

holds memory address of the next instruction to be executed

Question 13

CIR

Answer 13

holds current instruction being executed, divided into operand and opcode

Question 14

MAR

Answer 14

holds memory address of the instruction or data to be accessed

Question 15

MDR

Answer 15

holds the instruction or data that has been accessed from memory

Question 16

Fetch stage of FDE cycle

Answer 16

1) Memory address of next instruction is copied from PC to MAR via the address bus
2) Address in MAR is sent along address bus to RAM
3) Contents of the address (either a data or instruction) is sent along the data bus from RAM to MDR
4) Contents of MDR is copied into CIR
5) Address in PC is incremented to point to next instruction

Question 17

Decode stage of FDE cycle

Answer 17

1) Instruction in CIR is sent to control unit

2) Control unit interprets the instruction and splits it into opcode and operand.

Question 18

What is opcode

Answer 18

aka operation code – the command

Question 19

What is operand

Answer 19

the address or the data for the opcode to use

Question 20

What happens at end of each FDE cycle

Answer 20

Check for presenceof interrupts

Question 21

What is opcode represented as in assembly language

Answer 21

a mnemonic such as ADD or SUB