DOS ain't dead

XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB (Users)

posted by Japheth , Germany (South), 01.11.2011, 08:53

> It works with /X. It should work without /X though.
...
> The E820h map seems correct to me, so I'm not sure why HIMEMX needs to use E801h.

> 0000000000000000:000000000009F800:001
> 000000000009F800:0000000000000800:002
> 00000000000E7000:0000000000019000:002
> 0000000000100000:0000000003FFD800:001
> 00000000040FD800:0000000000002000:003
> 00000000040FF800:0000000000000400:004
> 00000000040FFC00:000000000BF00400:001

HIMEMX and old FD Himem stop scanning extended memory once a block starting at 0x100000 has been found. See lines marked with !!! below:


        mov eax,[di].E820MAP.baselow
        cmp eax,100000h ; has to live in extended memory
        setz dl         ;!!!
        jb @@e820_loop

        cmp esi,0
        jne @@e820_checkhole

; we're not able to handle extended base start not exactly at 100000h
;  not big deal to add support later (does this happen, though?)
        cmp dl,1
        jne @@e820_done ;!!!
        mov ebp,eax


I agree this is dumb, but that's exactly why the /X switch exists.

Would be interesting what XMGR does with that configuration.

It's also slightly interesting if the /X switch does really "work". Using Int 15h, ax=E801h, the memory used by ACPI at 0x40FD800 is overwritten once an application uses more that 64 MB. RBIL tells about types 03 and 04:


Values for System Memory Map address type:
 01h    memory, available to OS
 02h    reserved, not available (e.g. system ROM, memory-mapped device)
 03h    ACPI Reclaim Memory (usable by OS after reading ACPI tables)
 04h    ACPI NVS Memory (OS is required to save this memory between NVS


---
MS-DOS forever!

Complete thread:

• XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - Rugxulo, 25.10.2011, 21:28 (Users)
  • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - Japheth, 26.10.2011, 06:47
    • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - RayeR, 27.10.2011, 02:17
      • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - Japheth, 27.10.2011, 18:57
        • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - RayeR, 27.10.2011, 19:38
          • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - Rugxulo, 28.10.2011, 19:23
        • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - Rugxulo, 01.11.2011, 01:39
          • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - Japheth, 01.11.2011, 08:53
            • XMSDSK bug (HIMEMX > 2 GB): 100 MB RAM disk uses 1 GB - Japheth, 03.11.2011, 18:30