Re: Linux & X11 & IRQ Interrupts

From: David D. Hagood (
Date: Sun May 05 2002 - 20:33:33 EST

Justin Piszcz wrote:

> With the console speaker attached, it can be clearly heard, as well as
> performing fast packet movements (nmap (with insane option)) or such you
> can literally hear the packets.

What you are hearing is the noise in the computer's power supply. As the
load on the power supply changes, the voltage changes by a few tens of
millivolts, and that is the noise you are hearing.

This primary reason you don't hear this under Windows and you hear it
under Linux is that Linux will shut the processor off when there is
nothing to do, greatly reducing the load on the power supply. When
something happens, like a mouse interrupt or a network interrupt, the
CPU springs back to life, drawing a burst of power from the power supply
and momentarily bringing the voltage down a bit. This cycling of the CPU
happens in microseconds.

Windows, especially older versions of Windows, doesn't do this - when
there is no work for the CPU, it spins in a busy loop looking for work.
As a result, the load on the power supply never changes. Of course, your
system will also run hotter and burn more power.

If this bothers you, you could try getting another power supply (one
that is "stiffer" and less prone to voltage sag) or you could run a
program like Seti@home or Distributed.Net and keep your CPU busy all the

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This archive was generated by hypermail 2b29 : Tue May 07 2002 - 22:00:25 EST