[Coco] Coco Memory

[Aaron Wolfe]

the 8086 can address a full (normal) 1024k.  640k is what was left for
the user after the upper 384k was reserved by IBM for other purposes
(video memory, i/o, bios, etc).

the coco does essentially the same thing, for example in a "32k"
machine, i think about 28k is actually available.  i'm sure someone
here can given a more exact number :)

as for why the coco "couldn't do it", the addressable range of a CPU
and the amount of ram installed are often not the same.  the amount of
ram you can install is basically determined by how the motherboard or
memory card are designed, with the upper limit the address space of
the cpu (without bank switching and other tricks).   if you created
some functional memory device with a strange amount of ram on it, the
6809 on the coco could address whatever was there just fine.


On Sat, Jul 4, 2009 at 7:38 AM, Paul Fitch<pfitchjr at bellsouth.net> wrote:
> I've got a question that s been bothering me off and on for decades.
>
> The Coco under basic can easilly see 32k, and 64/128 K with ML routines.
> When the Coco3 came out, MS-dos intel machines using 8086/80186 processors
> could access and use 640k.  What was intel doing differently from Tandy to
> allow that odd non-base 2 memory amount? Ie, 1k, 2k, 4k, 16k, 32k, 64k,
> 128k, 512k, 1-meg, 2-meg.  640k falls in the middle there.  What were they
> doing that was so strange that the coco couldn't do it to?
>
>
>
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