PC Memory maps (was: Re: 486 w/newer IDE drives)
cisin at xenosoft.com
Fri Nov 24 15:17:52 CST 2006
> On 24 Nov 2006 at 14:07, Sean Conner wrote:
> > The major problem with that is MS-DOS---it can't handle non-contiguous RAM
> > and therefore there is no standard way to reserve or use memory in the upper
> > 384K of the address space (well, for those PClones that followed the IBM
> > spec).
MS-DOS CAN handle non-contiguous RAM, although in general applications
require contiguous chunks. It is possible to patch the memory allocation
linked list to show a non-existent TSR occupying the unavailable space.
Going past 640K requires some other minor patches.
Alternatively, as was mentioned, isolated chunks of RAM can be used for
various dedicated purposes, including "Expanded" memory, such as
JRAM, or the LIM spec.
On Fri, 24 Nov 2006, Chuck Guzis wrote:
> I seem to recall a few PCs with built-in CGA display adapters gave
> one more contiguous memory than 640K by filling the space between
> A000 and C000 with RAM. And many "not very compatible" PCs running
> MS-DOS made the entire 1MB available.
Stock CGA started at B800. With a suitably addressable RAM card, and some
trivial patches, it was possible to have contiguous RAM from 0 to B800.
Sorry, I can't find copies of the various patches.
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