Re: 3.3G RAM limit?

[David Brownlee <abs%netbsd.org@localhost>]

On Wed, 8 Apr 2020 at 22:27, Mouse <mouse%rodents-montreal.org@localhost> wrote:
>
> >> I have a fuzzy memory that there's some kind of limit that leads to
> >> i386 topping out at three-point-something gigs of RAM.  Could
> >> someone remind me of details?
> > It's got a single address space for user and kernel.
>
> Okay, that's one limit, but that doesn't explain the BIOS reporting
> only 3327M.  Of course, I don't expect people here to know the
> intricacies of Dell's BIOS, but the fuzzy memory indicated there was
> some hardware basis for this.  Perhaps that memory just got corrupted.

Running in 32bit mode there will be memory ranges reserved for PCI
address space. If the system is not remapping the "extra" RAM above
4GB then it will just completely ignore it.

Some BIOSs give control over how much space to reserve for video
memory and other PCI usage. I recall running NetBSD/i386 on very early
amd64 boards where I had something over 3900M of usable space after
BIOS tweaking.

On the other extreme the Intel XScale 80321 (arm) defaulted to 2GB of
PCI address space :)

David