Components Of The CPU

Question 1

What is the purpose of the control unit?

Answer 1

• coordinates all activities of the CPU
• Directs the flow of data between CPU and other devices
• sends read/write requests to memory
• coordinates and communicates with all parts of CPU

Question 2

What is the purpose of the programme counter?

Answer 2

• it is a register
• holds the address of the next instruction to be executed (either the next in a sequence or the address to jump to)
• at the start of each FDE cycle, contents of the register are copied to MAR

Question 3

What is the purpose of the MAR?

Answer 3

• it is a register
• memory address register
• holds the adress of the memory location to read from or write to
• sends address to memory down the address bus

Question 4

What is the purpose of the MDR?

Answer 4

• it is a register
• memory data register
• temporary stores data read from or to be written to memory
• sometimes called the memory buffer register
• all data going to and from memory must pass through this

Question 5

What is the purpose of the CIR?

Answer 5

• current instruction register
• it is a register
• contents of the MDR are copied here if it is an instruction
• contains opcode and operand of instruction

Question 6

What is an opcode and where is it?

Answer 6

• the information telling you what to do with the data
• the first half of the instruction

Question 7

What is an operand and where is it?

Answer 7

• the adress of the memory location with the data to be operated on in it
• the second half of the instruction

Question 8

What is the purpose of the ALU?

Answer 8

• performs arithmetic and logical operations on data, as well as binary shifts

Question 9

What is the purpose of the accumulator?

Answer 9

• it is a register
• one of the general purpose registers, where data or control information is stored
• the results of the ALU are often stored here

Question 10

What is the purpose of the address bus?

Answer 10

• unidirectional (data can only flow to memory)
• carries memory addresses that identify where data is being read from or written to

Question 11

What is the purpose of the data bus?

Answer 11

• bidirectional (data can flow both ways)
• carries the binary that makes up the information being transmitted around the CPU

Question 12

What is the purpose of the control bus?

Answer 12

• bidirectional (data can flow both ways)
• carries command and control signals to all components of the CPU