Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!att!cbnews!cbema!las
From: cbema!las@cbnews.ATT.COM (cbema!las)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Question about diskette densities
Message-ID: <7710@cbnews.ATT.COM>
Date: 23 Jun 89 17:09:12 GMT
References: <1559@cbnewsh.ATT.COM> <586@megatek.UUCP> <8428@killer.DALLAS.TX.US>
Reply-To: cbema!las@cbnews.ATT.COM (Larry A. Shurr)
Organization: AT&T Bell Laboratories, Columbus, OH (actually an AGS consultant)
Lines: 31

In article <8428@killer.DALLAS.TX.US> bobc@killer.DALLAS.TX.US (Bob Calbridge) writes:
>In article <586@megatek.UUCP>, hollen@zeta.megatek.uucp (Dion Hollenbeck) writes:
>+ From article <2210@bingvaxu.cc.binghamton.edu>, by vu0112@bingvaxu.cc.binghamton.edu (Cliff Joslyn):

>+ You didn't ask this, but it may help someone.  DSDD disks can be 
>+ formatted for up to 800k.  This is an unusual configuration because
>+ it uses 10 sectors per track which the UCSD p-System does reliably,
>+ but I never figured out why MS-DOS only used a max of 9 per track.

In order to make room for 10 sectors per track on 5 1/4 inch floppy
disks, you must reduce the gap between sectors to a value less than
the "standard" originally defined by IBM (let's see... I think they
called it 3740, yeah that sounds about right) for floppy disks.  Of
course, that standard was very conservative, having been tailored to
the capabilities of their very early tech 8 inch floppies (called -
surprise, surprise - the 3740).  

Advances in the state of the art had long since reduced the need for 
such conservative specs when IBM decided to go from 8 to 9 sectors 
per track on the PC, but apparently the old spec was too much of a 
barrier to cross.  It is, after all, an IBM standard.  It took a non-
IBM maverick company to go to 10 sectors per track, but the P-System 
was never really in the PC mainstream and it didn't have much of an
affect on the DOS mainstream.

regards, Larry
-- 
Signed: Larry A. Shurr (cbema!las@att.ATT.COM or att!cbema!las)
Clever signature, Wonderful wit, Outdo the others, Be a big hit! - Burma Shave
(With apologies to the real thing.  The above represents my views only.)
(Please note my mailing address.  Mail sent directly to cbnews doesn't make it.)