Date   : Mon, 09 Feb 2004 23:38:31 GMT
From   : Pete Turnbull <pete@...>
Subject: Re: Discs

On Feb 9, 22:53, Chris Thornley wrote:

> Shuggart Disk drives 3.5 inch
>   There are 5 types of 3.5 inch drive
>   (1)     The Quad Density Floppy (2.88MB) (1.44MB) (720KB)
>   (2)     The Standard High Density (1.44MB) (720KB)
>   (3)     The Tri or Multi Mode High Density Floppy (1.44MB)
> (1.2MB) (720KB)
>   (4)     The Standard Low Density Floppy (720KB)
>   (5)     Very Old Single Sided Disk Drives

> Type (3) Is a Tri mode high density floppy drive which operates at
300rpm
> and 360rpm and has two transfer speeds.

I've never seen a Type 3, except as a Teac 3.5"/5.25" combo.

> The high density drives contain a optical or mechanical media sensor
which
> instruct the drives to the correct transfer speed to operate in.

The data transfer rate is not controlled by the drive, but by the
controller.  The sensor just sets the density (and write current) and
sends a signal back to the controller to tell it whether it has a DD or
HD disk in.

> Disks can be fooled by placing some tape over the high
> density notch but they wont be as reliable as standard low density
> floppies.

Because of the different magnetic coercivities -- 600 Oersted for DD,
720 Oersted for HD, in the case of 3.5" media.  Higher still for quad
density, though I can't remember the actual figure.

You missed some.  The original Sony 3.5" drives had less than 80
tracks, and ran at 600 rpm, and were available as both single- and
double-sided.

> Shuggart Disk Drives 5.25 inch
>   There are 4 types of 5.25inch drive
>   (1)     The High Density Floppy (1.22MB)
>   (2)   Low Density 80Trk 96Tpi (720KB)
>   (3)     Low Density 40Trk       48Tpi (360KB)
>   (4)     Very Old Single Sided Disks Drives
>
> Type (1) Is a High Density Drive which can operate at 300rpm and
360rpm and
> has two transfer speeds.
> Type (2) Is a Low Density 98Tpi drive which can operate at 300rpm
with one
> transfer speed.
> Type (3) Is a Low Density 48Tpi drive which can operate at 300rpm
with one
> transfer speed.

Original Shugart (one 'g') drives were 35-track.  And both 40-track and
80-track drives were commonly available in both single- and
double-sided versions.  There are also 100tpi 80-track drives, as well
as 96tpi ones.

> On 5.25 drives if you put a logic 1 on pin 2 they should resort back
to
> there 300rpm modes and conversely a logic 0 will be 360rpm high
density.

Only Type 1 HD drives intended for PCs, but I think that's what you
meant :-)  It does, however, depend on the drive and its jumper
settings.  Some drives can be jumpered to only change write current, or
only change the speed, or to ignore the signal.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York