DA = "Data segment Alternate", or something like that. It refers to the segment register normally called ES, which string instruction implicitly use as destinat

DA = "Data segment Alternate", or something like that. It refers to the segment register normally called ES, which string instruction implicitly use as destination (source being DS unless overridden). The names are those used in a patent filed by Intel and come from before the official documentation for the 8086 was written. It might make the microcode a bit more readable to invent a different notation that is more in line with normal x86 assembly, but then again this is a very niche topic :)