Chapter 1 - Processor Components

Question 1

What is the purpose of the control unit?

Answer 1

To control and coordinate the activities of the CPU, directing the flow of data between the CPU and othe devices

Question 2

What is bus?

Answer 2

A set of parallel wires connecting two or more components of a computer

Question 3

What is the system bus?

Answer 3

The address bus
The data bus
The control bus

Question 4

What is the role of the control bus?

Answer 4

To transmit command, timing and specific status information between system components

Question 5

What is the role of the data bus?

Answer 5

To provide a bi-directional path for moving data and instructions between system components

Question 6

What is the role of the address bus?

Answer 6

To transmit memory addresses of words that are used as operands in program instructions

Question 7

What is the purpose of the ALU?

Answer 7

Performs arithmetic and logical operations on the data

Question 8

What are registers?

Answer 8

Special memory cells that operate at very high speed

Question 9

What is the purpose of the accumulator?

Answer 9

Results from the ALU are stored here

Question 10

What is the role of the program counter

Answer 10

Holds the address of the next instruction to be executed

Question 11

What is the role of the current instruction register?

Answer 11

Holds the current instruction being executed, divided into operand and opcode

Question 12

What is the role of the memory address register?

Answer 12

Holds the address of the memory location from which data is to be fetched or to which data is to be written

Question 13

What is the role of the memory data register?

Answer 13

Used to temporarily store the data read from or written to memory

Question 14

Describe the fetch phase inside the Fetch-Execute cycle

Answer 14

1) The address of the next instruction is copied from the program counter to the memory address register
2a) The instruction held at that address is copied to the memory data register.
2b) Simultaneously, the content of the PC is incremented so that it holds the address of the next instruction
3) The contents of the MDR are copied into the current instruction register

Question 15

Describe the decode phase inside the Fetch-Execute cycle

Answer 15

1) The instruction held in the CIR is decoded and split into opcode and operand
2) The opcode is used to determine the type of instruction and what hardware to use on it
3) The operand holds either: the address of the data to be used with the operation or the actual data to be operated on