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MASM Quick Start Registration Question - DX: AX

I am currently studying the exam that I will have on the x86 assembly.

I did not have much luck for googling for the ":", a punctuation mark that is too common: /

IDIV - Signed Integer Section

Usage: IDIV src

Changes flags: (AF, CF, OF, PF, SF, ZF undefined)

Signed binary division of the battery by source. If the source is a byte, AX is divided by "src", and the factor is stored in AL and the remainder in AH. If the source is the meaning of the word, DX: AX is divided by "src", and the factor is stored in AL and the remainder in DX.

Taken from Intel Opcodes and Mnemonics

What does DX: AX mean?

Thanks so much for your time :)

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2 answers

This is a pair of registers: DX and AX .

The numerator itself is a double word. The top word of the numerator should be stored in DX , the bottom word in AX .

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DX:AX is a 32-bit value used as the numerator of your division. The most significant 16 bits are stored in DX , the least significant in AX . This is a way to specify a 32-bit value in a 16-bit environment otherwise.

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