What is a register? Explain general-purpose and special-purpose registers.

A register is a small, very fast storage place inside the CPU that holds a word of data, an address or an instruction. It is made of flip-flops.

General-purpose registers (such as R0 to R15) can be used by the programmer for any purpose, such as holding operands, results or addresses.

Special-purpose registers have a fixed job. Examples are the program counter (address of the next instruction), instruction register (the present instruction), stack pointer (top of stack), memory address register, memory data register, accumulator and the status (flag) register.