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UDMA66 on Intel Chipsets


Ascii2

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Microsoft Knowledgebase article 247951 ( http://support.microsoft.com/kb/247951 ) specifies a tweak for Windows 2000/XP/Server 2003 to enable support for UDMA66 on Intel Chipsets on Intel chipsets.

The last sentence of the article states:

When you restart your computer, the UDMA66 mode will be enabled if the mode is supported by the hardware.

Is the sentence accurate? If devices on Intel chipsets with the tweak applied support transfer rates greater than UDMA66, would the devices be throttled to UDMA66?

EDIT: A rephrasing of the question for clarification:

The language of the Microsoft statement quoted earlier seemed to indicate that all devices capable of using Ultra DMA transfer rates UDMA66 or greater would use UDMA66 transfer mode on Intel chipsets with the EnableUDMA66 value set.

Consider the following conditions for the question that will follow:

  • An Intel Chipset supporting DMA transfer rates greater than UDMA66 is used.
  • A device supporting DMA transfer rates greater than UDMA66 exists on an IDE channel.
  • Intel Chipset drivers are not used (Microsoft drivers would be used and automatically installed).
  • The EnableUDMA66 value is set to "1" (enabled).

Would the device on the IDE channel transfer at a transfer rate greater than UDMA66 or be limited to a UDMA transfer rate?

Edited by Ascii2
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Are you having problems enabling higher UDMA than 66 on a particular Intel chipset, other than making sure your IDE cable, hard drive, and chipset all support the mode you're trying to use?

The EnableUDMA66 setting applies if you're using Microsoft's IDE driver (there is no EnableUDMA100 or EnableUDMA133 as far as I can tell). The limitation can be overcome by installing a proper driver from your motherboard or system manufacturer or Intel, the Intel Application Accelerator includes the driver and means to tweak UDMA modes.

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If devices on Intel chipsets with the tweak applied support transfer rates greater than UDMA66, would the devices be throttled to UDMA66?

For higher transfer rate, the motherboard and the device have to be "higher" than UDMA66 of course. If that was your question.

I believe UDMA66 was supported by motherboards from the PIII era (~1999) and after, quickly moving to UDMA100.

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If devices on Intel chipsets with the tweak applied support transfer rates greater than UDMA66, would the devices be throttled to UDMA66?

For higher transfer rate, the motherboard and the device have to be "higher" than UDMA66 of course. If that was your question.

The language of the Microsoft statement quoted earlier seemed to indicate that all devices capable of using Ultra DMA transfer rates UDMA66 or greater would use UDMA66 transfer mode on Intel chipsets with the EnableUDMA66 value set.

To have the question fully understood, I shall rephrase. Consider the following conditions for the question:

  • An Intel Chipset supporting DMA transfer rates greater than UDMA66 is used.
  • A device supporting DMA transfer rates greater than UDMA66 exists on an IDE channel.
  • Intel Chipset drivers are not used (Microsoft drivers would be used and automatically installed).
  • The EnableUDMA66 value is set to "1" (enabled).

Would the device on the IDE channel transfer at a transfer rate greater than UDMA66 or be limited to a UDMA transfer rate?

Edited by Ascii2
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You seem to know something we don't and that makes your question sound odd to me.

Why would you install "additional" support for UDMA66 on a motherboard that supports higher ?

XP surely provide drivers for higher transfer rates as well. So do you have a problem at first with an other device that needs UDMA66 (and not 100 or 133 like your mobo supports) ?

In my mind, if the mode being enabled doesn't mean it is active nor "forced".

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Why would you install "additional" support for UDMA66 on a motherboard that supports higher ?
Although, motherboard may support greater transfer rate, a device may not. If a device's maximum DMA transfer rate were UDMA66, then the UDMA66 Windows driver support would allow the device to use its maximum transfer rate.
XP surely provide drivers for higher transfer rates as well. So do you have a problem at first with an other device that needs UDMA66 (and not 100 or 133 like your mobo supports) ?
Currently no; my devices' maximum transfer rates are either lesser than or greater than UDMA66.
In my mind, if the mode being enabled doesn't mean it is active nor "forced".
My thinking is as follows: for a device to transfer at a select transfer mode, it must have the mode enabled and all other dependencies (chipset, drivers, BIOS, etc.) must have the mode enabled also.

If what you believe "enabled" refers to is equivalent to what the writer of the last sentence of the KB247951 article believed to be its meaning, then the language of the sentence does not restrict DMA transfer modes greater than UDMA66 on Intel chipsets.

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The question is not rhetorical, but there is no technical problem.

I do however want to know what the tweak specified in KB247951 actually does. If I were to include the tweak with my main Windows distributions, I should be sure as to its function.

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They were probably so thrilled they got it working that they forgot to assume that higher speed will appear. :rolleyes:

I always enable it and have seen devices with both lower and higher rates.

I *think* (after all, I'm not an insider) it enables, but not restricts to. B)

GL

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Thanks GrofLuigi.

This may be as close to knowing as possible for me for now.

I should be able to perform a test to determine the answer to the question posed in this thread without any uncertainty, but it would likely not be until a few months later.

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This is interesting because I have a computer with a Via chipset and even thought the motherboard, hard drive and cable support UDMA 5, in Windows XP it won’t go higher than UDMA 4. When I boot from the Western Digital CD it says UDMA 5 is active.

I’ve tried different cables, different hard drives, different ram, keyboards, monitors, mice power supplies. I’ve even put the motherboard into a different case and still when I install windows XP on this motherboard it only uses UDMA 4 mode. The bios and chipset drivers are the last ones provided by the manufacturer.

I’d given up long ago and just use it as it is but this thread made me wonder if this fix for Intel chipsets will work on a Via chipset.

Does anyone know if using the fix on a Via chipset will damage anything?

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This is interesting because I have a computer with a Via chipset and even thought the motherboard, hard drive and cable support UDMA 5, in Windows XP it won’t go higher than UDMA 4. When I boot from the Western Digital CD it says UDMA 5 is active.

I’ve tried different cables, different hard drives, different ram, keyboards, monitors, mice power supplies. I’ve even put the motherboard into a different case and still when I install windows XP on this motherboard it only uses UDMA 4 mode. The bios and chipset drivers are the last ones provided by the manufacturer.

I’d given up long ago and just use it as it is but this thread made me wonder if this fix for Intel chipsets will work on a Via chipset.

Does anyone know if using the fix on a Via chipset will damage anything?

Ultra DMA 4 is the same as UDMA66; if the tweak described in this thread were to work for you (unlikely), it would at worst force Ultra DMA 4. Edited by Ascii2
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This is interesting because I have a computer with a Via chipset and even thought the motherboard, hard drive and cable support UDMA 5, in Windows XP it won’t go higher than UDMA 4. When I boot from the Western Digital CD it says UDMA 5 is active.
Western Digital DataLifeguard reports, UDMA 5 Active (correct)

Windows XP reports, UDMA 4

Puppy Linux reports, SCSI

Sysdll, in an earlier post, you stated "Windows XP it won’t go higher than UDMA 4". Did you actually measure the transfer rate, or rely on Windows XP's DMA setting report. If you relied on the report, it is possible that you came to the worng conclusion (). It is not uncommom for Windows XP to misreport the specific DMA Mode being used; the hard disk may still transfer at a higher DMA mode than what is reported by Windows XP.

It is possible that Windows XP reports your hard disk channel using Ultra DMA Mode 4, but is using Ultra DMA Mode 5.

Edited by Ascii2
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Interesting, I’ve never tested it. This computer is an adequate web surfer so I haven’t bothered to pursue the UDMA 5 glitch. Does anyone know of a reliable utility (preferably freeware) to find out if it is the motherboard bios or XP that is in error?

The utilities I have don’t test anything they just repeat what the bios and OS report.

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