| What is control unit? | A component of the processor which is responsible for fetching, decoding and executing program instructions |
| What is arithmetic and logic unit? | A component of the processor responsible for arithmetic operations (Addition, Multiplication, Division, Subraction) and logical operations such as AND, OR, NOT. |
| What are buses? | A group of wires that carry data and instructions between the processor, memory and other devices |
| What are registers? | A special memory found inside processor, accessing the register can be done faster than accessing RAM |
| Name the 5 buses found in the processor? Give a short description for each | PC (program counter)
Holds the address of the next instruction to be fetched
MAR (Memory address register)
The address is held which data will be written or which data will be read from
MDR(Memory Data Register)
Contains data which will be written to the memory or read from the memory
CIR (current instruction register)
Holds the instruction which is currently being processed
ACC (Accumulator)
Holds the data while its being processed |
| What are the three buses in a processor? Give a short description for each | Control bus
Bi-directional
Bus is used to send instructions to the memory and other devices
Devices sends interrupts back to the processor through this bus
Address bus
Uni-directional bus
The MAR sends the address of the next READ/WRITE operation along this bus
Data bus
Bi-directional
It carries data between different components of the computer system |
| What happens during the fetch execute cycle? | Fetch -Copying the next program instruction from memory to CIR
1) The memory address in program counter is copied to MAR
2)The contents of the of the address given in the MAR is copied to MDR
3)The contents of the MDR is copied to CIR
4) Program counter increases by 1
Decode
Preparing to execute the instructions
Execute
The control unit sends instructions to the other devices telling them what to do |
| What happens during the execution of READ instructions? | The contents of the given memory address is copied to the accumulator
1) Address is loaded into the MAR
2) It is sent through the address bus, simultaneously a memory READ signal is sent through control bus
3) Contents of the memory address is sent through data bus to the MDR
4) Contents of MDR is copied to accumulator |
| What happens during the WRITE instruction ? | The contents of the ACC is copied to the given memory address
1)The memory address is loaded into the MAR and sent along the address bus to memory
2)Memory write signal is sent along the control bus
3)Contents of accumulator is sent to MDR and sent along the data bus to the memory
4) The data received on data bus is written to the given memory address |
