The Great Capacity Swindle

[bloodline]

HopperJF wrote:
Believe it or not it was as recently as 1997 that the most blank floppy disks were sold, the following year being overtaken by CD-Rs

Sounds about right... I was still buying floppies up to 2000... though not after... now I don't have a modern computer with a floppy drive... (/me leers at his old Althon64 3200 in the corner :-D).

[Sig999]

HopperJF wrote:
Believe it or not it was as recently as 1997 that the most blank floppy disks were sold, the following year being overtaken by CD-Rs

I can absolutely and totally believe it!  I left Australia at the end of 1997, and remember well the aftermath of Windows 95 - a LOT of folks I knew were really unhappy with it right after it's release (for reasons I don't know - I was still using my Ami and didn't really care that much).  But there was the hype of Windows 98 on the horizon, and not many folks couldn't afford CD-RW tech at that time for backups - I knew a lot of folks that were bulk buying floppies 'just in case'

[platon42]

bloodline wrote:

 Unfortunately, I only managed to get the encoding stable for the first 40 cylinders -- probably due to precompensation after this mark, the reading of the data was not stable. I gave up the project as floppies were becoming more and more obsolete at that time anyway.

Would precompensation really affect this? I would suggest that perhaps it was more likely that you might have made a calculation error that only showed up when the numbers got big enough. Not wishing to cast aspersions upon your code or abilities :-)

Well, the errors occurred exactly on the edge to cylinder 40 and *all* tracks after that were bad. AFAIK the floppy controller uses two or four different "zones" with different precompensation, switching at exactly half through the disk. I'm pretty sure it was no calculation error (and 40/80 is not even a power of 2, nor a big number).

[Zac67]

I understand you used no write precompensation at all? Then that's probably the cause. Local velocity of the medium increases constantly inward - on track 40 you have a ~35% higher speed, rising to nearly double speed on track 80. I'd guess even three different precomp zones would be necessary. Nice project though. ;-)

[bloodline]

Zac67 wrote:
I understand you used no write precompensation at all? Then that's probably the cause. Local velocity of the medium increases constantly inward - on track 40 you have a ~35% higher speed, rising to nearly double speed on track 80. I'd guess even three different precomp zones would be necessary. Nice project though. ;-)

Ahhh, right! I assumed that either Paula or the drive electronics itself would have handled the Precompensation... but Paula is very simple... so I guess everything has to be done in software... Makes you glad that Floppies have gone really! :-)

[HopperJF]

I still use floppies fairly often, although that is no secret really  :lol:

[monami]

i'm glad to see floppies go. i bought 2 new boxes of 40 from argos a few years ago. 2 different makes. and lots started to show bad sectors after a few uses. i had to keep them as i developed a problem where i couldn't return faulty goods! (part of my ocd.) i didn't see how it was possible for them to be faulty brand new and out of the box. odd.

[platon42]

Zac67 wrote:
I understand you used no write precompensation at all? Then that's probably the cause. Local velocity of the medium increases constantly inward - on track 40 you have a ~35% higher speed, rising to nearly double speed on track 80. I'd guess even three different precomp zones would be necessary. Nice project though. ;-)

I used the trackdisk.device RAW (MFM) writing routines to avoid having to hack paula registers directly, so they should cater for precomp automatically... but who knows why it failed. It was a nice experience getting that low level