The CPU has four internal registers, each of 16 bits. The first four, AX, BX, CX, and DX are common use registers and can also be used as 8 bit registers, if used in such a way it is essential to refer to them such as: AH is the high and AL is the low bytes of the AX register. This nomenclature is also appropriate to the BX, CX, and DX registers.
The registers identified by their particular names:
AX Accumulator
BX Base register
CX Counting register
CS Code segment register
BP Base pointers register
SI Source index register
DI Destiny index register
DX Data register
DS Data segment register
ES Extra segment register
SS Battery segment register
SP Battery pointer register
IP Next instruction pointer register
F Flag register