[prev in list] [next in list] [prev in thread] [next in thread] 

List:       freebsd-hackers
Subject:    Re: Compaq 16MB limit...
From:       Terry Lambert <terry () lambert ! org>
Date:       1996-01-31 21:00:20
[Download RAW message or body]

> Problem: When a Compaq has 64 Meg DRAM in it, BSDI does not see it all.
> It only see's 16Meg.. The BIOS say's hat there is 64 BUT BSDI says 16..
> 
> I have been told that FreeBSD has fixed this somehow... Can somebody
> please tell me 'approx' which files to look at in the kernel source
> code to see how it was done ????

Compaq and Dell have decided that their historical misuse of a couple
of CMOS bits constitutes "acceptable practice".  As a result, the max
memory you see when you query the CMOS is 16M (or 32M for non-bogus
machines).

The POST reports the RAM correctly because the BIOS can be written to
use hardware specific mechanisms to report the RAM.

There is no documented API to return the amount of RAM in a machine
other than CMOS.  There is no BIOS routine that can be used by the
boot blocks to overcome this limit, nor does the POST place the results
of its test or expose a ROM routine for sizing memory.


FreeBSD "fixes" this problem by allowing you to mandate the amount of
RAM in the machine and force it to ignore the (standard) CMOS mechanism
for sizing RAM.  See /sys/i386/conf/LINT for details.


UnixWare fixes this by allowing you to make a one line entry in a
configuration file in the /stand "bootfs" partition -- it's similar
to the FreeBSD "fix", except that you don't have to rebuild the kernel.


In more recent (or future) versions of FreeBSD, this may be specifiable
at the boot "-c" interface for device reconfiguration.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.

[prev in list] [next in list] [prev in thread] [next in thread]