32-bit x86 assembly programming: Difference between revisions

Revision as of 22:14, 25 May 2004

Revision as of 23:57, 17 June 2004

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All of them can be used both for segmented addressing of memory and for holding data. Some of these registers are however better to use for certain operations than others. This is because mnemonics using certain registers could be translated into shorter [[opcode]]s than if they used other registers.

The lower 16 bits of each 32 bit register can be addressed seperatelyseparately and like a register in its own right, and these 16 bit registers can be broken up into two eight-bit registers - that is 16 bits of data in a 16 bit register can be addressed 8 bits at a time: the upper eight and the lower eight bits, and can be treated as registers in their own right.

If we take the EAX register, this register contains 32 bits and the lower 16 bits can be addressed by the AX register. The upper 8 bits of the AX register can be addressed by the AH register and the lower 8 bits of the AX register can be addressed by the AL register.