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SubjectRe: detecting > 64M on x86

On Mon, 23 Dec 1996, Mark Hemment wrote:

> On Mon, 23 Dec 1996, Kimon Berlin wrote:
> > "Larry M. Augustin" <lma@varesearch.com> wrote:
> > > For example, the int 15h ah=c7 get memory map call returns a 42 byte
> > > structure that includes how much memory is installed above and below
> > > the 16M boundary.
> > Ralf Brown's interrupt list says this is a PS/2 function
> > "Standard" functions are int 15h, ax=e801h and int 15h, ax=e820h. e820h is
> > closest to c7h, it returns a detailed memory map, but it has to be called
> > several times, this would bloat setup.S . I think e801h would be enough
> > for our purposes,
> >
> > Would there be a point in reporting the amount of cachable memory? I don't know
> > if any other part of the kernel is designed to have a use for that (i.e. "fast
> > pages" and "slow pages").
>
> The memory sub-system isn't designed for fast/slow pages, but having the
> information available would be v. useful.
> From time-to-time, the question pops up; "I've installed extra
> memory, and Linux runs slower!", and answer is (nearly) always due to
> pages not being cached (not enough tag-ram, etc). If Linux could
> display a warning for this condition, I'd vote for it.
> The page allocation routines could also be modified to try and avoid
> giving out slow pages, and start paging out when 'fast' pages become low
> - a very simple solution, and probably wouldn't work v. well...
>
> > > No, I don't know the difference between local and system memory, and I
> > "Local" would be on the motherboard, "system" on another board. Before memory
> > modules (SIPPs and SIMMs), when you wanted more memory, you added an ISA (or MCA?)
> > card with memory chips on it. Bandwidth was, um, suboptimal.
>
> Would there still be systems out there which have this archiecture? I
> somehow doubt it, but watch out for the up coming NUMA machines. Each
> 'node' will have local memory, but will be able (at a cost) to access
> memory on other 'nodes' (a single address space).
>
I sold my last intel above boards (isa memory crap) three years ago...
full sized isa boards with 2MB 130ns memory (laugh) ... sold 'em to some
not-so-computer-oriented dummy... for $30 ;)
Those stinky cards were _really_ slow... hope I'll never see 'em again ;)

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