Subject: Re: fclk speed
To: Chris Gilbert <firstname.lastname@example.org>
From: Richard Earnshaw <email@example.com>
Date: 08/26/2002 11:22:13
> Not sure if others were already aware of this tweak, but in the BIOS/cyclone of your cats box there's an option called fclk. It seems that fclk controls the clock for the footbridge. This clock also drives the clock speed for the memory. by doing:
> set fclk 66
> in the bios I got a 32% increase in memory bandwidth. From what I can tell the bios defaults to 50MHz.
> Obviously you need PC66 DIMMs.
> Just thought I'd share this little gem.
I remember playing with this switch only to find that it doesn't do
anything useful. However it does
1) Mess up serial lines
2) Make "sleep 30" take about 40 seconds
3) Make 'time <cmd>' lie about how long it really took.
If you get different results on your machine please let me know (so I can
grab a newer copy of the firmware).
All of the above are consistent with the fclk environment variable in the
bios being just a constant that is passed at boot time. To really change
your fclk I think you have to flip a switch on the motherboard.