[sci.electronics] The differences between hard drives

cyamamot@aludra.usc.edu (Cliff Yamamoto) (04/12/90)

Greetings!

This question has probably appeared before, but I have never heard
a realistic answer to it.

I was going to get a Perstor 180 controller to run ARRL (31 sec/trk)
using a ST4096.  I've called Perstor and they say it works but when I
asked if they *guarantee* my drive will work, they refused.  "We can't
guarantee the quality of hard disks put out from manufacturers".  Ok
made sense.  But why do they sell controllers like this in the first
place? (QUESTION #1).

So I called Seagate to see if they had any qualms about it.  The guy
said he's heard of people running MFM drives at higher capacity, but
Seagate doesn't recommend it (ok.. sounds familiar).  I asked what's
the difference between MFM and RLL?  He tells me just the electronics
since data rates and density are different.  I ask him about media
differences and he says both MFM and RLL use the same type of media
nowadays.  Well can't the analog portions of the disk electronics be
"retuned" to run MFM, RLL, ARLL or ESDI? (QUESTION #2).

Well I could have saved about $330 going the Perstor way (180-16FN
with ST4096).  But since I've not been convinced that ARLL can be
*safely* run on a MFM drive, I went out and ordered a WD10007-SE2
with a 1355 Micropolis drive.  I'm sure I should be 'more safe' with
this ESDI combination.  Yet I'm still curious; how does "tuning" the
electronics for a particular drive affect the magnetic patterns on
the disk? (QUESTION #3).  Does the read/write head require more
current to generate higher flux?  (QUESTION #4).  Or is even the
physical geometry of the read/write head on a MFM vs. RLL entirely
different? (QUESTION #5).  Do the amplifiers on the analog board
need to be of higher gain for different encoding formats or is
just higher bandwidth necessary? (QUESTION #6).

This turned out longer than I wanted but I since I shelled out $330
more, I want to feel "justified" that there is some legitimate
technical reason why higher capacity drives cost more even though
others may be doing the same with their MFM drives (at a greater risk??!?)

Please reply via email or post to these newsgroups (I hope others may
be interested in this info as well).

Clifford Yamamoto - KA6JRG		Email:	cyamamot@aludra.usc.edu
Jet Propulsion Labs				cyamamot@devvax.jpl.nasa.gov
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