From: Michael Sokolov <sokolov@alpha.CES.CWRU.Edu>

<Arno Griffioen <arno@usn.nl> wrote:
<> [...] (or much, much less in the case of a certain 
<> brain-dead PC drive interface type.. Hint: start's with an 'I' and
<> ends with 'DE' ;-)
<I agree wholeheartedly! I use 5.25" full-height ESDI Winchesters on my IB
<AT-compatible at home, and I will never use the bull**** called IDE.

that is the single most inaccurate statement I've heard to date.

The IDE interface is a simplification of the combined wd1003 or 100x(the 
rll cards) and the associtaed MFM drive. From the bus and programatcally 
they look the same and for all intents and purposes they are the same.  
However as IDE drives moved forward the data rates from platters went up 
to exceed the EDSI rates and most all have some level of track buffering 
or caching (there are ISA16 caching controllers but the data rates are 
limited to either MFM or EDSI).  Unless dma is used the peak data rate for 
an ISA16 interface is limited to the bus speed and not the maximum 
transfer rate of the drive.  IDE being off the ISA bus can run at higher
rates.  The newer 3.5" drives offer lower seek times, lower rotational 
latency than any 5.25" drive and are only exceeded in performance by 
their contemporary SCSI drives.

What's apparently wrong about IDE (applies to ISA16) is that PCs do 
PIO(most cases) rather than DMA transfers so concurantcy is lost to 
CPU cycles doing the transfers rather than DMA.  

Having a linux box with a Ultrastor caching edsi controller using a 
Micropolus 1664-7 5.25 edsi and a WD 420mb 3.5" IDE in the same box 
there is no question which is the faster and it's not the EDSI.  That 
proved true for both linux and DOS.  In my expereince for nonPC platform 
design the performance levels are MFM -> EDSI -> IDE -> SCSI-III with MFM 
at the bottom of the pile.

Don't blame IDE for bad performance as it's a hardware bus level interface 
standard only and it's limits are well into the 20mb/S plus range and is 
only limited by the hardware on either side of it.  On the otherhand it
is fair to say XYZZ IDE drive is poor performer as that can be very true
especially in the older drives.


Allison