The number and nature of registers is a major factor which distinguishes among computers. For illustration, Intel Pentium has about 32 registers. A number of these registers are special registers and others are general-purpose registers. A number of the basic registers in a machine are:

• All von-Neumann machines have a program counter (PC) (or instruction counter IC) which is a register that contains the address of the next instruction to be executed.
• Most computers use special registers to hold the instruction(s) currently being executed. They are called instruction register (IR).
• There are a number of general-purpose registers. With these three types of registers a computer will be able to execute programs.
• Other types of registers:
• Memory-address register (MAR) holds the address of next memory operation (load or store).
• Memory-buffer register (MBR) holds the content of memory operation (load or store).
• Processor status bits indicate the current status of the processor. A number of times it is combined with the other processor status bits and is called the program status word (PSW).