machine instruction cycle

Question 1

how are computer systems stored in primary memory

Answer 1

as a series of instructions in machine code

Question 2

what needs to happen for a computer program to operate

Answer 2

the instructions in the primary memory needs to be moved into the CPU - fetch-execute cycle

Question 3

4 steps in machine instruction cycle

Answer 3

1. fetch instruction from primary memory to control unit
2. decode instruction in control unit
3. execute instruction
4. store result of execution and check for next instruction

Question 4

what happens in the fetch phase of the machine instruction cycle

Answer 4

CPU sends appropriate address through the address bus to primary memory
instruction that resides in the address is copied into the data bus and is sent to the control unit

Question 5

what happens in the decode phase of the machine instruction cycle

Answer 5

instruction received by the control unit is decoded
any required data that need to be loaded from the primary memory in order for the instruction to be executed is then fetched
address of these data are placed into address bus and data from these addresses are received by the CPU through data bus

Question 6

why is decoding an instruction necessary

Answer 6

it allows the CPU to be aware of any additional data that are necessary for execution of the instruction

Question 7

what happens in the execute phase of the machine instruction cycle

Answer 7

CPU executes the instruction using the data that have been loaded and calculates a result - depending on this result, additional data may be needed
addresses of these data are placed in the address bus and data from these addresses are received by the CPU through data bus

Question 8

what happens in the store phase of the machine instruction cycle

Answer 8

CPU stores the result in primary memory by specifying the address where the result will reside in primary memory using the address bus and then sends data through data bus