[sci.electronics] MFM vs RLL vs IDE vs ESDI vs SCSI

phil@brahms.amd.com (Phil Ngai) (09/20/90)

In article <2132@bnlux0.bnl.gov> scottc@bnlux0.bnl.gov (david scott coburn) writes:
|In other words, why should the data transfer rates for a RLL disk with a
|host-resident RLL controller differ from a RLL disk with an embedded
|SCSI controller?

It wouldn't, assuming it was a SCSI RLL system and ignoring caches.
But many SCSI system are not simply MFM or RLL. A popular technique
these days is ZBR (zone bit recording) where the data per track
actually increases as you move from the inner to the outer tracks.
Such "geometries" would hopeless confuse DOS but SCSI can hide it.

Another trick is to increase the RPMs, typically from 3600 to 5400.
(ever calculate the rotational latency at 3600 RPM?)

Finally, ESDI systems range from 10 Mbits/sec to 15 and up. A SCSI
system coupled to such a fast disk could easily outperform MFM
or RLL. If you have the bucks.

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Phil Ngai, phil@amd.com		{uunet,decwrl,ucbvax}!amdcad!phil
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