Re: 64-bit DOS extender?

From: KVP (spamtrap_at_crayne.org)
Date: 09/29/04

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    Date: Wed, 29 Sep 2004 06:20:23 +0000 (UTC)

    "Wiktor S." <spamtrap@crayne.org> wrote:
    > >> I just wonder, would it be possible to create something
    > >> similar to emm386 emm386 and a 64-bit DOS extender for
    > >> AMD64 processors?
    > > Something like DPMI or DOS4GW would be rather trivial,
    > I think it shouldn't much differ from existing 32-bit extenders -- just
    > different mode switching routine?

     Yes, a switch from 16 bit real mode to 16 or 32 bit protected mode,
     then a switch to long mode, then to 64 bit long mode.

    > > but a real mode emulation would be way more complicated since
    > > there is no v86 mode available when long mode is active.
    > Is there something wrong with so called "compatibility mode", to run
    > 16/32-bit software on 64-bit systems? Why it would "way more complicate"
    > things?

     The long mode supports only 16 and 32 bit _protected_ mode. There is no
     support for real mode or v86 mode. Every extender willing to use the bios
     or other real mode software have to either return to real mode or switch
     back to 32 bit legacy mode, and use v86 mode from there. Either way, a
     simple bios call requires at least four mode switches and two separate
     paging systems switched on every mode switch, just to work.

      Viktor

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