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On Wed, May 23, 2001 at 02:09:36PM -0500, Wolford, Jeff wrote:
> Re: PIO Mode
> a) The host is in complete (almost) control of the PIO timing
> (IORDY could stretch it out), so the drive has no idea
> what mode the host is actually using (just an fastest upper bound).
>
> The only way that I think the drive could know this
> info is if the host wrote it to the drive.
Related question: what's the purpose of the SET FEATURES command that
tells the drive what mode the host is going to use? Does it change
drive behavior at all? I can imagine ways the drive could use the
information to increase performance, but do they really?
The host isn't required to issue that SET FEATURES, is it?
> b) For PC storage PIO is not used (except for boot):
> i) Significant HDD performance impact
> ii) When using Intel Pentium II or later processors, it is
> very difficult to support faster than 16X CD-ROM drives
> let alone 48/52X CD, or 16X DVD drives
> iii) DAE (digital audio extraction) even at 1X is very difficult in
> PIO
Someone correct me if I'm wrong... Didn't Windows 9X ship with DMA turned
off by default? And even W2K appears to leave it off by default for most
ATAPI devices. Linux left it off by default until recently. That's most
of PC Storage right there that's not using DMA.
jcastle
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