From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 5 May 2002 21:33:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 5 May 2002 21:33:36 -0400 Received: from oak.sktc.net ([208.46.69.4]:33040 "EHLO oak.sktc.net") by vger.kernel.org with ESMTP id ; Sun, 5 May 2002 21:33:36 -0400 Message-ID: <3CD5DD6D.60800@sktc.net> Date: Sun, 05 May 2002 20:33:33 -0500 From: "David D. Hagood" User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.9+) Gecko/20020413 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Justin Piszcz CC: linux-kernel@vger.kernel.org Subject: Re: Linux & X11 & IRQ Interrupts In-Reply-To: <3CD5D57D.DED89DFC@starband.net> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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 time.