Summary: 32-bit OS addressing > 4GB of RAM

From: Darryl and Teresa Pace (
Date: Sat Jul 15 2000 - 05:59:58 CDT

Thank you to all who replied. They were:

Darren Dunham
Kevin Buterbaugh
Bill Hathaway
John Sullivan
Casper Dik

My question was:
        Solaris was a 32-bit operating system prior to Solaris 7,
and thus processes running on those earlier versions of Solaris
were limited to an address space of 4 GB. Physical memory,
though, had to be addressed. In those earlier versions of Solaris,
how was it possible to address all the memory in those boxes that
contained greater than 4 GB of RAM (e.g., a 24 CPU, 24 GB memory

The answer was:
     Quoting from Adrian Cockcroft's "Sun Performance and Tuning, 2nd
Edition" page 140 ... "How can this be? The answer is that the SuperSPARC
memory management unit maps a 32-bit virtual address to a 36-bit physical
address, and the UltraSPARC memory management unit maps a 32-bit virtual
address to a 44-bit physical address. While any one process can only
access 4 Gbytes, the rest of memory is available to other processes and
also acts as a filesystem cache."

Again, thanks.

-- Darryl

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