rwessel (rwessel.delete@this.yahoo.com) on October 1, 2021 6:19 am wrote:
>
> The 386 had a 48(-ish*) bit virtual address space, but that was mapped into a 32 bit linear address
> space. Increasing the size of the linear address space would be been fairly trivial, and essentially
> invisible from the application layer (given the era, it's obvious why they wouldn't have initially
> defined the linear address space bigger than 32 bits). Not really unlike how the 286 had a 32(-ish*)
> bit virtual address space mapped into a 24-bit physical address space (and how a 16-bit OS could have
> used the 386 enhancements to address more than 24-bits worth of memory, without using any "32-bit"
> feature of the CPU - just extra, previously unused, bits in the descriptor tables).
>
> I don't think anyone ever actually did it, but ideas for mapping more than 4GB worth
> of segments into a process using PAE hacks were tossed about in the late x86-32 era.

The only reason nobody bothered to do that on the 386 is that no systems decoded more than 4GB of RAM and address space. 4MB 32 pin SIMMs did not show up until the 486 and that would not be dense enough. We certainly did it later.