Payen Joel's question on ATA and 4 drives

Steve Finch TFINCHS%A1.VAX2T.mrouter at
Tue Jan 18 08:19:33 PST 1994

Joel Payne wrote
"The capability of ATA to support 4 drives is described in Western Digital
documents "Enhanced IDE implementation guide" (august 93) and "Enhanced
IDE 1993/1994".  So "Enhanced IDE" is meaningful and "Enhanced ATA" seems
like a new topic...  If anyone is aware of a given standard on this topic
let us know."

I have always found Western Digital's approach to the ATA/IDE market
interesting and confusing.  The WD documents I have seen merge together 
several interesting and important concepts:  more than two drives, higher
speed transfers and CD-ROM device support.  The three are described 
together and one could get the impression that they must be adopted 
together.  They have succeeded in not only confusing the customers but also 
the vendors as well.  

The method of putting 4 drives on ATA, is really putting two ATA interfaces
on a machine and placing 2 drives on each interface.  Nothing new here, as 
this has been around for a long time.  There is an annex in the dpANS ATA-2 
document that lists the addresses used for some PC implementations (be 
careful, as these address are believed to be incorrect and should be 
updated in the very near future (by March?)).

Higher speed transfers (to 11.1 megabytes/sec PIO, 13.3 megabytes/sec DMA) 
are also in the dpANS ATA-2.

The support for CD-ROM is currently an SFF activity, which is nearing 
completion.  It is expected that SFF will submit the CD-ROM proposal (named 
the ATA Packet Interface or ATAPI) to X3T10 for standardization very soon.  
I expect that this information will be incorporated into ATA-3 activities.

I don't know how many times I've had to answer similar questions on the 
phone....   If only WD wouldn't make its statements and make them seem like
they reflect the beliefs of the entire industry...  But it is often hard to 
slow down the outflow from a broken dam. 

The above comments are mine alone, and not a reflection of my company.

(I'll wait for the shot's fired by WD for my point of view.  Ain't it great 
to live in America?)

Steve Finch, Silicon Systems, Inc.
PH:  714 573-6808, FX: 714 573-6914, Email:  5723283 at

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