STRUCTURE OF THE PROCESSOR

Question 1

What is the function of the control unit?

Answer 1

• coordinates all activities of CPU
• directs flow of data between CPU and other devices
• accepts next instruction, decodes it, handles its execution and stores resulting data back in memory/registers
• sends memory read and write requests to main memory on control bus as well as other commands and control signals (eg: bus requests, bus grants, etc.)
• coordinates and communicates with all parts of CPU

Question 2

What is the function of the program counter (PC)?

Answer 2

holds address of next instruction to be executed (could be next instruction in a sequence of instructions/address to jump to if current instruction is a command to jump/branch

Question 3

What is the function of the memory address register (MAR)?

Answer 3

• holds address of memory location from which data is to be fetched/to which data is to be written
• sends address to memory down address bus

Question 4

What is the function of the memory data register (MDR)?

Answer 4

• used to temporarily store data which is read from/written to memory
• all data to and from memory must travel down data bus and pass through MDR

Question 5

What is the function of the current instruction register (CIR)?

Answer 5

• holds current instruction being executed
• contents of MDR copied into CIR if its an instruction
• contains opcode and operand(s) of current instruction to be executed
• instruction = opcode + operand

Question 6

What is the function of the arithmetic logic unit (ALU)?

Answer 6

• performs arithmetic (+) and logical (boolean) operations on data
• bitwise shift operators left and right ( x and ÷)
• often uses general purpose registers to temporarily hold results of calculations

Question 7

What is the function of the accumulator (ACC)?

Answer 7

• general purpose register (CPU may have many for storing temporary data while instructions/calculations are being carried out. typically, the more general purpose registers in a CPU the faster it operates)
• often stores data/control info
• temporarily stores results of calculations carried out by ALU

Question 8

What is the function of the address bus?

Answer 8

carries memory addresses that identify where data is being read from/written to

Question 9

What is the function of the data bus?

Answer 9

carries binary 1s and 0s that make up actual info being transmitted around CPU/computer

Question 10

What is the function of the control bus?

Answer 10

carries command and control signals to and from every other component of the CPU/computer