Mailinglist Archive: opensuse (3637 mails)

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Re: [SLE] ATA 100 vs. UDMA 33/66
  • From: quintaq@xxxxxxxxxxx
  • Date: Mon, 7 May 2001 11:17:48 +0100
  • Message-id: <20010507093632.4C305DF923@xxxxxxxxxxxx>
On Sun, 6 May 2001 15:48:16 -0700
Ben Rosenberg <ben@xxxxxxxxx> wrote:

> Yes, I use hdparm. It seems to work quite well. You can enable it in
> YaST2 if you have 7.1 and it seems to work pretty well. My IBM Deskstar
> that replaced the Maxtor that died works quite very fast.


I did some searching on this theme a while ago. Here are three posts from the kernel list I found useful.


On Wed, 24 Jan 2001 dmeyer@xxxxxxxxxx wrote:
> The kernel always says:
> ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
> at boot time. How would I know if it's safe to say idebus=66? The
> documentation is fairly vague on this.

When the manual for your mainboard states that clock settings for setting
up your CPU creates a change in the normal idebus=33MHz of any other
value, then you are probablely safe. Since all 32-bit PCI busses run at
33MHz, as last thought and reported, it should not be needed to change.
If I recall the idebus=XX primary use was for VLB/ISA/EISA systems, but I
have been wrong before.
Andre Hedrick

On Wed, May 24, 2000 at 12:33:37PM -0700, Dr. Kelsey Hudson wrote:
> You didn't read that error message well enough. :)
> Look, you can pass a kernel parameter on boot with the
> idebus=33
> option to tell it to go to UDMA/33 instead of UDMA/66.
You didn't read that error message well enough. :)
(in fact, maybe it's not your fault, but the massage is a little bit
idebus doesn't set UDMA speed, it sets the system bus speed that is
used in ide timing calculations. From ide.c:
 * ide_system_bus_speed() returns what we think is the system VESA/PCI
 * bus speed (in MHz). This is used for calculating interface PIO timings.
 * The default is 40 for known PCI systems, 50 otherwise.
 * The "idebus=xx" parameter can be used to override this value.
 * The actual value to be used is computed/displayed the first time through.

Camm Maguire <camm@xxxxxxxxxxxx> writes:
> Greetings! The above chipset is reported as supporting ATA-66 under
> linux at But the specs at via's website indicate
> that this is a UltraDMA33 chipset. I may not be understanding my
> terms correctly, but can one set 'idebus=66' with this chipset under
> linux with the current ide patch?

No. That idebus parameter is to tell the kernel the ACTUAL PCI bus speed
which is the same clock that the IDE interface uses, if you set it to 66
while your PCI is at 33, strange things may happen. I never checked what
actually happens, but among the possible outcomes are:

slow disk

data loss

no transfer at all, IDE resets

Don't do it. Set idebus to your actual bus speed as per your mainboard
jumpers (or switches or other settings). It should be 33, if you're
overclocking, it might be 37 or 40 but this renders your entire hardware
Matthias Andree

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