[Tfug] question about idebus= thingy :)

[John Gruenenfelder]

On Thu, Jan 16, 2003 at 05:33:32PM -0700, Jeremy wrote:
>	Ok, like most people I find watching my linux boot up sequence to be 
>a riviting experience. I noticed mention of and idebus parameter where I 
>could pass to the kernel the speed of my IDE bus (it's just "assumes" 
>33, mine's 133). Is setting this a good idea? I can't find much on 
>google (at least not in english :). I've got a via 686 chipset which I 
>know isn't the world's best, so I hesitate tweaking things I know little 
>about as there's lots of things on a via board that get turned off by 
>default since they don't actually work. If I add idebus=133 or even just 
>idebus=66 can I expect to get lots of errors on my harddrive? Heck, is 
>it even worth the trouble/will make a difference?
>
>	While I'm on the suject of chipsets, anyone know where in town I can 
>find a good Socket 370 sdram board to replace the crappy but servicable 
>DFI board I've been using :). Everything seems to be DDR lately.
>
>	Thanks yet again.
>
>Jeremy Gregorio

Actually, your IDE bus speed is *not* 133MHz. This is, without knowing more
about your CPU, the speed of your MEMORY bus.  The IDE bus speed is usually a
factor of the memory speed.  In this case, 1/4.  Setting the idebus parameter
to anything significantly away from 33 will very likely cause your IDE bus to
not function at all, since IDE is designed to work at 33MHz.

For example, on my last motherboard (BP6), I had a Celery 366 that runs at a
memory bus speed of 66 MHz.  The IDE factor is thus 1/2.  I overclocked this
to a memory bus speed of 97MHz (couldn't quite make it to 100) and thus a CPU
speed of 533Mhz.  The BIOS was smart enough to then run the IDE bus at a
factor of 1/3 rather than 1/2.  However, you'll note that 1/3 of 97 is
actually 32.33 MHz.  This is really close to 33MHz, and since most of my
storage devices were on SCSI, I never bothered to set the idebus parameter.
However, this is the sort of situation where you would actually use that.


-- 
--John Gruenenfelder    Research Assistant, Steward Observatory, U of Arizona
                        johng@as.arizona.edu
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