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In article <3992@brazos.Rice.edu> murthy@algron.cs.cornell.edu (Chet Murthy) writes:
>X-Sun-Spots-Digest: Volume 8, Issue 228, message 4 of 18
>Does anybody out there know how to increase the max datasize per process
>limit under SUNOS 4.0?  I have a sun-4/260 here with 1.6Gigabytes of swap,
>and I'd like to use most of that for a really big symbolic processing job.
>I'm currently getting a "mere" 512MB (1/2 Gig) right now per process.

It looks like you have run into a hardware limit.

I found the following in "Writing Device Drivers", Part No: 800-1780-10,
Revision A, of 24 April 1989 (which is part of the 4.0.3 "Change Pages and
Addenda to the Docubox", Part No: 800-3378-10, Revision A of 24 April
1989).

Pages 79 and 80, topic "Selecting a Virtual to Physical Mapping", says
that the Sun-4/260 has two virtual address spaces of 512 magabytes in
size.

The diagram on page 85 shows the block diagram of the Sun-4 MMU.  It shows
that the context register plus 12 high address bits are used to index into
the segment map and look up a 9 bit quantity.  These 9 bits, plus 5 middle
address bits, plus 13 low address bits = 27 bits = 2**27 words = 128 mega
words = 512 mega bytes.

The manual said nothing about the Sun-4x architechure; maybe it has a
larger virtual address space.  But it looks like you are maxed out on your
4/260.

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