Date   : Tue, 18 Dec 1990 19:57:00 CST
From   : LANCE TAGLIAPIETRA <TAGLANCE@ucs.UWPLATT.EDU>
Subject: uniform and 8 inch cpm formats on AT controllers

X-News: ucs.uwplatt.edu comp.os.cpm:204
 
>From: tom@astro.as.arizona.edu (Thomas J. Trebisky)
>Subject:Re: uniform and 8 inch cpm formats on AT controllers
>Date: 18 Dec 90 04:44:55 GMT
>Message-ID:<748@organpipe.UUCP>
 
>Michael_D._Sprague sprague.wbst311@xerox.com writes:
>>
>>> The 1.2M floppy format uses the same data-transfer rate as an 8" drive
>>> (500Kbits/sec). This is also true for 1.44M drives.
>>> 360K floppies use the standard 250Kbits/sec.
>>Hmmm, I knew both of those, but what is the transfer rate for a quad density
>>drive?  I assume 250K bits/sec?
>
>I believe what is refered to as quad-density is also known as a 720k drive,
>(the nomenclature is a bit sloppy, quad density means different things in
>different contexts) and indeed has a 250kb/s xfer rate - the density being
>acheived by higher track density (96tpi instead of the usual 48tpi).
>
>BTW, for you transfer rate trivia freaks, did you know that a floppy written
>on a 360kb drive and later read on a 1.2M drive (AT, HD 5.25in) has a xfer
>rate of 300kb/s since the 1.2M drive rotates at 360 rpm, but the 360kb drive
>rotated at 300rpm - this in part explains why you can read 360kb floppies on
>such drives, but may have trouble writing to them (the other part is probably
>the slimmer heads on the 1.2M drive).
 
I thought that 1.2M floppy drives had a speed select line that allowed the
speed to be switched between 300rpm and 360rpm.....O.K. here it is from an
article in "The Computer Journal" from issue 44, page 17:
 
         ... It [a 1.2meg drive] is an 80 track double-sided drive,
         that, when pin 2 is pulled low, increases its rotational
         speed to 360 rpm.  At the same time, the NEC 765 floppy
         controller doubles its data rate to 500K bits/sec, and writes
         15 sectors of 512 bytes/sector.
 
Since pin 2 is normally low, the drive ends up spinning at 360 rpm, unless
allowed to change in the controller hardware (a speed select latch??).
 
Lance Tagliapietra