Re: CBM 8280

From: William Levak (
Date: 1999-08-31 03:25:40

On Mon, 30 Aug 1999, Nicolas Welte wrote:

> Geoff Oltmans wrote:
> > I thought the "QD" format on 5.25" disks still used DD disks, only with
> > double the number of tracks (80 vs. 40)?
> Not exactly, real QD disks were tested and approved for that track
> density. I think they are physically the same as DD disks, but were more
> expensive.

The question often occurs:  What is the difference between the various
densities since the coating seems to be the same for SD, DD and QD.  Also
what is the difference between single and double sided since there is a
magnetic coating on both sides of single sided disks.

The best answer I have seen was in the letters column of Electronics Now
several years ago by a former employee of one of the manufacturers.
He stated that the most expensive part of disk manufacturing is the
testing and certification.  Single sided disks are not disks that
failed on the second side, but disks that were never tested on the second
side.  Double density disks are disks that were tested at double density, 

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