DOS ain't dead - ROM-BIOS leaves ds and es limits beyond 64 KiB

ROM-BIOS leaves ds and es limits beyond 64 KiB (Developers)

posted by ecm , Düsseldorf, Germany, 28.10.2025, 22:03

> One fun trick is to write to VGA buffer space using a single 32-bit
> instruction while in Unreal Mode.
>
> mov ebx,A0000> mov [ds:ebx], byte 1 ; set the pixel "white" using default color palette >

I can read from the word at segment 0 offset B8000 to read the text mode buffer. I just checked again, ds and es have higher limits, cs, ss, fs, and also gs do not. Also, the ROM-BIOS identifies itself as "Award Medallion BIOS v6.0", "Copyright (C) 1984-2000", running an "ASUS MED 2001 ACPI BIOS Revision 1009". At the bottom of the startup screen it reads "06/12/2001-VT694X-MED 2001".

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Complete thread:

ROM-BIOS leaves ds and es limits beyond 64 KiB - ecm, 28.10.2025, 17:20 (Developers)
- ROM-BIOS leaves ds and es limits beyond 64 KiB - Oso2k, 28.10.2025, 21:46
  - ROM-BIOS leaves ds and es limits beyond 64 KiB - ecm, 28.10.2025, 22:03