Format for IBM display writer disks??

From: Don Maslin <donm_at_cts.com>
Date: Fri Jan 19 00:53:41 2001

On Thu, 18 Jan 2001, Wayne M. Smith wrote:

> > On Thu, 18 Jan 2001, Wayne M. Smith wrote:
> >
> > > My S/23 Service Manual states that two 8 inch
> drives
> > > were available, the 31SD which was a single sided
> FM
> > > only drive, and the 51TDF which was a double sided
> FM
> > > or MFM drive. The disks have 77 tracks per side,
> and
> > > data can be written on tracks 1 through 74, with 00
> > > reserved for labeling and 75 and 76 for
> replacement.
> > >
> > > Both drives are hard sectored. FM disks can be
> > > formatted with 8, 15 or 26 tracks, with 512, 256
> and
> > > 128 bytes per track respectively. For MFM the
> bytes
> > > per sector are doubled.
> >
> > I believe that you mean SOFT sectored, as the number
> of sectors
> > per track in a hard sector disk is determined by the
> disk and
> > is only changeable by using a disk with a different
> hole pattern.
> > FYI, 5.25" disks came in both 10 and 16 sector hole
> patterns,
> > while 8" were 32 hole only to the best of my
> knowledge.
> >
> > - don
>
> My S/23 manual says the following:
>
> "The location of the access hole for index sensing on a
> diskette [type] 1 differs from that on a diskette
> [type] 2 and diskette [type] 2D." The 31SD drive can
> only read type 1, so I guess you could say it's soft
> sectored (I assume it ignores the hole). The 51TD
> reads types 2 and 2d, which have the same hole pattern
> vis-a-vis each other, but different from a type 1, but
> also reads type 1. It distinguishes based on the
> location of the index hole, so I would say it was hard
> sectored. Then again, in effect it's only determining
> DS vs. SS so maybe that's not the same thing. What do
> you think?
 
Wayne, what they are discussing is the aperture in the disk
jacket that permits seeing the index and/or sector holes.
On the Single-Sided disks that aperture is 7degrees clockwise
from 12 0'clock. On the Double-Sided disks it is 26 degrees
clockwise. Double-Side drives have sensors in both positions
and can therefore read either single or double sided disks.
On the other hand, Single-Side drives have only a single sensor
at the 7 degree position.

In a Hard-Sector 8" disk there are 32 evenly spaced sector holes,
plus 1 index hole that is centered between two of the sector holes.
To all intents and purposes, the only difference between a single
and double sided Hard-Sector disks is the location of the aperture.

                                                 - don
Received on Fri Jan 19 2001 - 00:53:41 GMT