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On Wed, 23 May 2001 15:18:44 -0600, Jim Castleberry wrote:
>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?
Yes, there have been drives that required the Set Features command
otherwise they would not operate properly at PIO mode 3 or 4 speeds
(they would corrupt data). This is why to this day a host should
always issue the Set Features command if it really wants to use PIO
mode 3 or 4.
>The host isn't required to issue that SET FEATURES, is it?
Not required but it is the safe thing to do. And it is only a few
bytes of code and takes all of a few microseconds.
>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.
Most ATAPI devices seem to be operated at PIO mode 0 even on new fast
systems. And because most ATAPI devices are very slow (even a 50x CD
is extremely slow) and because ATAPI devices generally do not work on
the same cable with another device this really should not be a big
problem, certainly not a bit impact to hard disk performance on the
same system.
*** Hale Landis *** [EMAIL PROTECTED] ***
*** Niwot, CO USA *** www.ata-atapi.com ***
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