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SubjectRe: (U)DMA Explained (Re: Kernel freeze on boot (.123-.125) in IDE init)
On Thu, 22 Oct 1998, Chip Salzenberg wrote:

> According to Andre M. Hedrick:
> > Are IBM-DAQA-33240 and WDC AC31600H are UDMA by default???
> > If they are, you need to move them off the 430HX PIIX3.
> > This silly controller thinks that it can do UDMA, because it can decode
> > the difference in the hardware. However, you would have seen (U)DMA if
> > you could turn off in the BIOS timing settings.
> Could you unpack that? You see, I also own an ABIT IT5H 1.5, and I
> also have a drive that reports as "(U)DMA". When I "hdparm -d1" that
> drive, it keeps working -- but is it really using UDMA?

UDMA is not enabled, but DMA mode 2/1/0 is enabled.
This is the only chipset that I have had false reports on (U)DMA
functionality, first hand..........Tyan Tomcat III S1563D SMP Bios 4.01/2.

"(U)DMA" means that it is capable, but has not been enabled in the BIOS.
Since the PIIX3 on 430HX systems can detect the difference, it does so.
The docs from Intel clearly state, this chipset is hardware limited to
DMA mode 2 or PIO 4 Fast-ATA. There are no future updates to support UDMA
since IMHO that have closed production.........

Andre Hedrick
The IDE-FNG for Linux
The APC UPS Specialist for Linux SUSPENDED

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