Xref: utzoo comp.sys.ibm.pc.hardware:7393 comp.multimedia:308 comp.misc:12028
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!masscomp!peora!tarpit!bilver!bill
From: bill@bilver.uucp (Bill Vermillion)
Newsgroups: comp.sys.ibm.pc.hardware,comp.multimedia,comp.misc
Subject: Re: Diffs between DD & HD disks
Message-ID: <1991Apr9.042503.18670@bilver.uucp>
Date: 9 Apr 91 04:25:03 GMT
References: <1991Apr6.170017.24990@news.iastate.edu> <1991Apr6.234019.2894@agate.berkeley.edu> <571@lysator.liu.se>
Organization: W. J. Vermillion - Winter Park, FL
Lines: 35

In article <571@lysator.liu.se> zap@lysator.liu.se (Zap Andersson) writes:
>THere is SOME thruth to this, however:
>
>Most diskette manifacturers use the same media for 1.44 and 720k disks.
>However, a test is done on each disk, and if it falls below a certain
>threshold in reliability, they go in the 720k bucket, otherwise they
>will become 1.44 Meg's.....
>

The testing you mentioned used to be done to separate Single Sided
from Double sided, back when a goo 88k 5.5" disk cost $5.00 each.

Get some spec sheets from a diskette manufacturer and you will see
that there ARE differences in the magnetic media between DD and HD.

Typically the DD's are about 600 oersted coercivity while the HDs
are in the 700 oersted range.

The problem with ad's like that is they perpetutate falsehoods.
A little over a year ago Jerry Pournelle espoused the same thing in
his Byte article.  He could have easily picked up the phone an
called Sony (one of the larger 3.5" disk mfrs) and gotten the
correct information, but he just said the same thing you did.

I have spec sheets from at least BASF and CENTEC and there ARE
differences, not matter what the ad's say.

You can get by with this (sometimes) better than those who tried to
use 360's at 1.2 meg in the 5.25" world.  Those are about 300
oersteds for the DD's and 600 for the HD's.  As a matter of fact
the 5.25" HD media is just about identical to the 3.5" DD media.

-- 
Bill Vermillion - UUCP: uunet!tarpit!bilver!bill
                      : bill@bilver.UUCP