3 types of buses
| Address bus | It is unidirectional, and is used to transmit memory addresses within the CPU to and from RAM. |
|---|---|
| Data bus | It is bi-directional and carries data from the CPU to memory (and vice versa) |
| Control bus | It is bi-directional and is used to transmit control signals that are sent by the CU (control unit) |
Components in a CPU
(3.1.2)The Von Neumann model has several components that are used in the fetch‑execute cycle. One component is the [Insert Component]. Describe the role of the [Insert Component]. [3 or 4 marks]
| Components | Role of Component |
|---|---|
| Arithmetic & Logic Unit (ALU) | Carries out calculations [1m] and logical operations [1m] and holds intermediate values during calculations [1m] that is stored in a register called the accumulator [1m] |
| Control Unit (CU) | Controls operation of memory, processor and Input/output [1m] where instructions are interpreted [1m] and signals is sent to other components telling them what to do [1m] |
| Register | Role of the register |
|---|---|
| CIR, Current instruction register | This register stores the current instruction being decoded and executed. |
| ACC, Accumulator | This register is used when carrying out ALU calculations. It stores intermediate data during the calculations. |
| MAR, Memory address register | This register stores the address of the memory location currently being read from or written to. |
| MDR, Memory data register | This register stores data which has just been read from memory or data which is about to be written to memory. |
| PC, Program counter | Stores the address where the next instruction to be read can be found |