DOS ain't dead

OS/2 extender (Developers)

posted by Rugxulo , Usono, 10.09.2025, 21:30

> Physical Address Extension (PAE): To allow 32-bit systems to use
> more than 4 GB of physical RAM, an extension called PAE was developed.
> With a PAE-enabled kernel, the OS could access up to 64 GB of physical
> memory, but each individual 32-bit process was still limited to its
> 4 GB virtual address space.
>
> For a time, there was a specialized Application Binary Interface (ABI)
> called "x32" that ran on 64-bit AMD64 machines.
> Pointers and performance: The x32 ABI used 32-bit pointers for
> compatibility and efficiency, which limited the memory of a single
> process to 4 GB. However, it still provided access to the full set of
> 64-bit registers, which could offer a performance boost for specific
> workloads.

Realistically, if there is a speed advantage to AMD64 (despite wasting more memory with bigger pointers), it just varies. The apps also tend to be noticeably larger.

For DOS, I imagine you'd load the data into memory, switch to 64-bit mode to do calculations, then switch back and write the data in memory to file (if needed).

Then again, yet another option is to use SIMD (SSE2) for 64-bit math.
Although 64-bit integer math is also easy to do with 32-bit regs.

Yet another idea is to use VT-X in 64-bit mode to "emulate" DOS.

So there is no huge need for AMD64 support in DOS.

Complete thread:

• OS/2 extender - kerravon, 10.09.2025, 21:05 (Developers)
  • OS/2 extender - Rugxulo, 10.09.2025, 21:30
  • OS/2 extender - Ringding, 11.09.2025, 17:44
    • OS/2 extender - kerravon, 11.09.2025, 17:57
      • OS/2 extender - Ringding, 11.09.2025, 20:41
        • OS/2 extender - kerravon, 12.09.2025, 00:08
          • OS/2 extender - Rugxulo, 12.09.2025, 04:07
            • OS/2 extender - kerravon, 12.09.2025, 16:55
          • OS/2 extender - Ringding, 12.09.2025, 17:20
            • OS/2 extender - kerravon, 12.09.2025, 18:03