As explained in the Overview of Computers unit, registers are a very important part of CPU because:
  1. They have very fast access time,

  2. They are directly linked to the control unit and ALU,

  3. Hence, instructions that utilize registers for operands' storage execute faster than instructions which utilize the main memory for operand storage.
Registers are connected to other units in the CPU through an internal data bus.

Intel's processors 8086, 8088, and 80286 had 16-bit registers, while latter generations (80386, 80486, Pentium, II, III, IV) have 32-bit registers. These are called IA32 (Intel-Architecture 32) and contain numerous improvements over the older generations.

The new IA32 processors maintain backward compatibility with the older x86 processors (i.e. programs that utilize older x86 16-bit registers will still run on newer IA32 microprocessors).

Next, the different x86 registers are reviewed followed by the IA32 registers.