General purpose registers

Depending on the mode of the operation (protected or long), there are 8 to 16 available general purpose registers in modern Intel processors. Each register is divided into subregisters, allowing access to data with a bit width lower than the width of the register.

The following table shows general purpose registers (further referred to as GPR):

For convenience, we will refer to the registers by their 32-bit names (such as EAX, EBX, and so on) when we do not need to explicitly refer to a register of a certain bit width. The preceding table shows all general purpose registers available on the Intel platform. Some of them are only available in the long mode (all 64-bit registers, R* registers, and a few of the 8-bit registers) and certain combinations are not allowed. However, despite the fact that we can use those registers for any purpose, some of them do have a special meaning in certain circumstances.