The CPU

The CPU (Central Processing Unit) is the hardware that executes programs and manages the rest of the hardware.

Von Neumann used the idea of holding programs in memory and data would then move between the memory unit and the processor.

It’s Volatile - data is lost when turned off. Stores user data/programs/part of operating system which is currently in use. Memory can be written or read from.

Random Access Memory

ALU (Arithmetic Logic Unit) CU (Control Unit) MDR (Memory Data Register) MAR (Memory Access Register) PC (Program Counter) Accumulator (ACC) Current Instruction Register (CIR)

Logical Operations: These include AND, OR and NOT Shift Operations: The bits in a computer word can be shifted left or right by a certain number of places Arithmetic Operations: These include addition, subtraction, multiplication and division

The Memory Address Register holds the address (location in memory) of the instruction or piece of data to be fetched or stored. When the data or program instruction is fetched from memory, it is temporarily held in the Memory Data Register.

The Program Countermholds the memory address of the next instruction to be executed, which has heen fetched from memory and it temporarily held in the MDR before before being copied to the CIR.

The Accumulator is one of the general purpose registers in which data and results of many operations are temporarily stored.

The Control Unit decodes the instruction in the CIR to see what has to be done next.

The instruction is executed. Depending on what the instruction is, this could, for example, involve fetching data from memory and loading or addimg it into the accumulator or jumping to another instruction in the program.

The address A of the next instruction to be executed is copied from the PC to the MAR. The PC is incremented so it piints to the next instruction to be fetched. Simutaneously, the onstruction held im location A is then copied into the MDR. The contents of the MDR are copied to the CIR.