🚀 go-pugleaf

In article <WAYNE.90Feb27094326@dsndata.uucp> wayne@dsndata.uucp (Wayne Schlitt) asks:
>what is the difference between "main" memory and "expanded" memory?
>if "expanded" memory is just a back store for paging and disk cache,
>then i dont think that including "expanded" memory is what people
>normally think of as "physical memory".  (you can also exclude ram
>disks and the memory on high res video cards)
>
On IBM 3090s (probably the mainframe that the previous poster had in mind)
"expanded storage" is RAM which is not directly addressable, but is moved
in 4Kbyte chunks to and from directly addressable storage by synchronous
instructions. It is used by MVS and VM as a very-high-speed paging device;
microcode assists can do the transfers without a software page fault in
some circumstances.

If someone would like to explain what the economic advantages are to 
providing extra storage in this form, I would be interested to listen.


Chris Thompson
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