Skip to main content
Retrocomputing

You are not logged in. Your edit will be placed in a queue until it is peer reviewed.

We welcome edits that make the post easier to understand and more valuable for readers. Because community members review edits, please try to make the post substantially better than how you found it, for example, by fixing grammar or adding additional resources and hyperlinks.

Required fields*

13
  • 9
    Technically, long mode can run 16-bit protected mode code, just not virtual 8086 code. For the Windows-specific case, the 16-bit Windows APIs are still not available in 64-bit Windows, but this isn't a CPU limitation. (DOS applications, on the other hand, are real/virtual 8086 and won't work without emulation.) Commented Jun 9, 2016 at 23:53
  • 5
    "you can't simply pretend AL and AH are separate 8-bit registers unless you avoid DIV, MUL etc. entirely" -- of course, the 8080 didn't have any such instructions anyway, so you'd probably be avoiding them as a matter of course. Commented Jun 10, 2016 at 19:21
  • 1
    @Jules yes indeed, if you're porting 8-bit code — I was thinking more along the lines of developing new 8-bit code. The same consideration applies to the 16- to 32-bit switch, and to the 32- to 64-bit switch, since they all introduced new instructions that don't have smaller equivalents, so I suppose my argument is contrived. Commented Jun 10, 2016 at 19:23
  • 2
    @Radovan I’m mentioning DOSBox and Wine in the context of emulating the operating system services, not the CPU. You’re right about DOSBox emulating the CPU (DOSEMU does so too in some circumstances, since it’s hard to run 16-bit code in VM86-mode while in long mode on 64-bit CPUs). Commented Aug 11, 2017 at 12:50
  • 1
    Windows 10 32 bits edition supports 16 bits applications. One can say that it's its "raison d'être". That version exists mainly for that purpose, as x86 without 64 bit support (Athlon XP, Pentium 4, Dothan, etc.) would be so slow anyway that there would be no point in installing windows 10 on them. Commented Apr 27, 2020 at 9:50