Is >16MB possible on ISA box (ISC 2.2.1)?

[Conor P. Cahill]

richard at pegasus.com (Richard Foulk) writes:

>Okay, so ISC blew it.  It IS possible to run ISA bus Unix with greater
>than 16 megs of memory.  DMA is not a necessity.  I've seen people
>reporting 24 megs and more, in this forum, on ISA bus machines.

I wouldn't say ISC blew it.  The original System V 3.2 only supports up to
16 MB and requires changes to support additional memory.  Somewhere along
the way ISC decided that the market for >16MB on an ISA bus is too small
to justify the additional effort required to support it.

As far as I know, SCO is the only vendor to support > 16 MB (although I
don't know if it will work on ISA bus systems, but I think it will). SCO
did this by using the "epanded memory" trick that is used by many dos
systems (it copies a page down below 16MB whenever a page is accessed
by a bus operation).  This works the same way under EISA systems, even 
though it isn't necessary there.

On the other hand, ISC has committed to supporting > 16MB on many EISA systems
in full native mode in release 2.3. (An update disk that works for several
EISA MBs, but fails on some others is available.  A more general one is 
in the works - no word on the actual release date).

>So what is the real situation today?  Which 386 ports of Unix will support
>greater than 16 megs on the ISA bus?  (Did the MEMRANGE spec actually
>vaporize with ISC's 2.2, or is it just hiding somewhere else?)

The MEMRANGE spec went away in 2.2, but I don't think it worked correctly
in 2.0.2.  We set up a system with 32MB of memory and a 12MB ram disk.  When
we went above 4MB of processes, the system crashed.  One of my distributors
told me that they did a similar test with no ram disk and the system 
crashed when they went above 16MB of processes/kernel.  So while the 
system said it saw more than 16MB, it appears that it did not use it 
correctly.

-- 
Conor P. Cahill            (703)430-9247        Virtual Technologies, Inc.
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