Date   : Wed, 09 May 1990 16:29:00 CDT
From   : LANCE TAGLIAPIETRA <UCSLCT@UWPLATT.EDU>
Subject: disk drives

Hi,
 
Michael D. Kersenbrock (michaelk%copper.wr.tek.com@RELAY.CS.net)
replied to my inquiry, and I though others might be interested:
 
#In article <9AC642E1815F4000B3@uwplatt.edu> you write:
#>Rex_E._Robards.DlosLV@Xerox.com writes:
#>
#><1.44 MB diskettes have 18 sectors per track.  720 KB diskettes have 9
#><sectors per track.  3.5" drives and 5.25" drives have the same pinouts
#><(they are indistinguishable).
#>
#>Yes, I understood from the article that 1.44Mb disks are putting 18
#>512 byte sectors on a track, and 720Kb disks are putting 9 512 byte
#>sectors on a track. The article explains that the data rate is
#>doubled.
#>
#>What is physically different between a 1.44Mb drive and on that is
#>rated at 720Kb?   Why can one handle the doubled data rate, and not
#>the other?
#
#1. Probably has a smaller-gap'd head for the more compressed flux reversals.
#
#2. Has circuitry to detect HD media, and to appropriately change the
#   write-current level (HD needs higher flux levels, I understand).
#
#These changes are minimal, and usually the 720K drive and 1.44MB drive
#will cost the same or with very little difference in price.  I don't see
#why anyone would buy a 720K drive.
#
#>Looking at a 3.5in drive here, I would say that the pinout has to be a
#>bit different than a 5.25in drive, and the 3.5in drive has no power
#
#The little "converter" board that makes my 3.5" drive fit into a 5.25"
#PC slot looks like a straight 1-for-1 translation of connector signals.
#
#>connector like the 5.25in (at least the ones connected to the ps/2's
#>here don't).
#
#Yes it does, again, it's just a different connector type.  The adapter
#cable on mine just has a small square-pin connector at one end, and the
#traditional 5.25" power connector on the other end, with four non-twisted
#wires going straight accross.  The pinouts between the two types of
#drives seem indentical except for the connector *types*, and maybe pin #2
#of the data connector.  The adapter board has a jumper for that signal
#so that I can connect it or not.  This may not have to do with drive
#types, though, I recall it being a difference in signal interpretation
#between AT's an XT's (or was it PS/2's?).
 
 
Thanks to Rex E. Robards, Michael D. Kersenbrock, and David Goodenough
for their replies.
 
Lance Tagliapietra  ucslct@uwplatt.edu or ucslct@uwplatt.bitnet