Re: Random device in 1.3.31 on [34]86...

Theodore Ts'o (
Fri, 13 Oct 1995 03:22:23 -0400

From: Marek Michalkiewicz <>
Date: Tue, 10 Oct 1995 20:21:12 +0100 (MET)

If I am reading the 1.3.31 patch correctly, the random device now uses
the cycle counter on a Pentium to get some more randomness. In 1.3.30
the high resolution timer (present in all PCs) was used for that, but
this code has been removed completely (instead of using in only on
non-Pentium systems). For those poor people without Pentimus (myself
included), shouldn't we still use the timer?

The problem is that the timer is very slow to access, so it
significantly increases your interrupt latency; unfortunately, this
happens on the slower machines which may ill-able to afford the extra
speed hit. Without the timer, randomness accumulates much more slowly,
but it doesn't hurt your system as much.

The next version of the random driver will have the old timer code, but
it will still be ifdefed out. People who want it badly enough can ifdef
it back in....

- Ted