kjcsb wrote: > I wish to disable MMX on my FC4 system. How do I do that preferably without > having to build the kernel from source? Any advice appreciated. Erm -- what, why, and to what purpose? This is a pretty unusual request, so don't expect anyone to have anticipated it (by giving -noMMX flags). The easiest way would probably to use something like qemu to emulate an entire pre-MMX system. MMX isn't used that much in Linux. Using MMX instructions means that a programmer has to effectively code the routine in assembler code, *and* provide an equivalent C routine for processors (PowerPC and other non-x86 machines, and "classic" Pentiums and earlier) which don't support MMX. On top of that, using MMX means that you can't use normal x87 floating point maths without a relatively lengthy switch. So either a program has to be using no floating point, or there has to be a serious gain from MMX to make it worth the switch. On top of that, it only makes sense where you've got a program that has a lot of matrix-style integer maths to do -- enough that switching to MMX gives a user-noticeable speed-up. (gcc has recently gained support for "auto-vectorization" -- spotting where it makes sense to use SIMD instructions like SSE, and reorganising the code to make best use of them. See http://www.redhat.com/magazine/011sep05/features/gcc/#vectorization-flags for details. I've never heard about auto-vectorization using MMX.) There are packages which use MMX -- for example, gstreamer uses the liboil library, which will use whatever's available. The kernel also occasionally uses MMX instructions, if they are available. And without some sort of virtualisation (e.g. qemu), you can't fool the kernel. You might be able to patch the kernel so it identified the processor as one without MMX -- if you really want to do that, your best bet is to contact the kernel mailing list, explaining what you really want to do (otherwise they'll start looking for user-space solutions, which would make a lot more sense), and explaining that you're not a C programmer. You should probably disable SSE and 3D-Now while you're at it. Hope this helps, James. -- E-mail address: james | "Drums must never stop. Very bad if drums stop." @westexe.demon.co.uk | "Why? What will happen if the drums ever stop?" | "Bass solo."
