Built-in Assembler Register Symbols
In Turbo Pascal's built-in assembler, the following reserved symbols denote CPU registers:
AX BX CX DX 16-bit general purpose
AL BL CL DL 8-bit low registers
AH BH CH DH 8-bit high registers
SP BP SI DI 16-bit pointer or index
CS DS SS ES 16-bit segment registers
ST 8087 register stack
When an operand consists solely of a register name, it is called a register operand. All registers can be used as register operands.
The base registers (BX and BP) and the index registers (SI and DI) can be written within square brackets to indicate indexing.
These are valid index register combinations:
The segment registers (ES, CS, SS, and DS) can be used in conjunction with
the colon (:)to indicate a different segment than
the one the processor selects by default.