Inside the processor

Inside the processor

1. Registers

   • Areas of memory within the CPU itself
   • Work at extremely fast speeds so can be used by the processor without causing bottle neck
   • Program Counter
     • Keeps track of the memory location of the line of machine code being executed
     • With each iteration of the FDE cycle it gets incremented to point to the next instruction, allowing the program to be executed in sequence, one by one
     • Changed by instructions that alter the flow of control
   • Memory Data Register
     • Stores the data that has been fetched or stored in memory
   • Memory Address Register
     • Stores the address of the data or instructions that are to be fetched from or sent to
   • Current Instruction Register
     • Stores the most recently fetched instruction, waiting to be decoded and executed
   • Accumulator
     • Stores the results of calculations made by the ALU
   • General Purpose Registers
     • These can be used to temporarily store data being used rather than sending data to and from the comparatively much slower memory

2. Buses

   • Data bus carries data between the processor and memory
   • The address bus carries the address if the memory location being read from or written to
   • Control bus sends controls signals sent from the control unit
     • Control unit sends out signals co-ordinating how the processor works, it controls how data moves around parts of the CPU and how ut moves between the CPU and memory, instructions are decoded in the CU