[wellylug] VAX data floppy>USB transfer, but no FD

[Ewen McNeill]

On 2013-04-15 22:24 , Ewen McNeill wrote:
> On 2013-04-15 13:52 , Adam Bogacki wrote:
>> [s]ingle sided, double density (80 tracks/135 TPI), StorageMaster (TM)
>> 1262-00 floppy disk. [...]
>
> [I]'d have expected a single sided, double density disk of that age
> (CP/M, so 1980s) to be 5.25" and have 40-ish tracks.  [....]
> suggests that it might be a VAX RX50 disk, which was single sided 80
> tracks (that they call quad density;

One final thing I meant to note.  Quad density had the same track 
density (and magnetic coercivity) as double density, it just crammed 
twice as many tracks into the same area (with the same number of sectors 
per track), so various people would write quad density onto 
double-density media.  Particularly once quad density media stopped 
being manufactured beyond a special item.  ("High density", ie PC 1.2MB 
5.25" media was _not_ compatible; it was designed for a different 
magnetic coercivity, and so only worked with high density drives, and 
had more sectors per track.)  Thus even if the media is labelled SSDD, 
it's at least plausible it actually has quad density on it if (a) it was 
written on a VAX and (b) it is single sided 80 tracks.

You will probably not be surprised to learn that writing quad density 
onto disks manufactured for double density did little to improve the 
readable lifetime :-)  (At least Control Data was one of the better 
respected floppy disk vendors, so you have that in your favour.)

Ewen