[Coco] Oddball disk format question

[Neil Morrison]

This could be done on a Model III or a Coco. The programs Trakcess,
SuperUtility or Power Tool could all do this. I suspect AnaDisk could do it
on a PC also.

Neil

----- Original Message ----- 
From: "Robert Gault" <robert.gault at worldnet.att.net>


> Does anyone know how it might be possible to create a track where the
> track ID number does not match the disk location, the sectors have
> values 247 & 248, and there is data on sector 248?
>
> I have determined the following. The track can be created by stepping to
> the desired location (T35) and issuing a Write Track command with an
> incorrect track value. The Coco controller will accept a sector value of
> 248 even though it is not "legal. A sector with a value of 247 = $F7
> (which is a reserved Western Digital command) can coincidentally be
> created if the track ID is 164 when a crc is requested in the "wrong"
> place. $F5, $F5, $F5, $FE, $A4, $F7 will create $A1, $A1, $A1, $FE,
> $A4(track) ,$42(side), $F7(sector) because the crc of $A1A1A1FEA4 is
> $42F7. It is not possible to place the desired data on sector 247 during
> a format because it contains values in the range $F5-$FE and I can't
> access the sector with a disk zap program because of the mismatch
> between disk and track IDs.
>
> This track actually exists and I'm speculating that it was not created
> on a Coco but on a more advanced computer with a more powerful disk
> controller. Any thoughts from the audience?