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Forums > C64 Coding > Write a Disk backwards
2019-06-20 10:31
oziphantom

Registered: Oct 2014
Posts: 409
Write a Disk backwards

Is it possible to write a disk backwards, say take a D64 probably pre flipped and write it backwards. Maybe run the stepper motor backwards?
 
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2019-06-20 12:25
Krill

Registered: Apr 2002
Posts: 1522
My bad. Doesn't answer the question, though.
2019-06-20 12:30
oziphantom

Registered: Oct 2014
Posts: 409
I'll add more words

The goal is to write an image with the 1571 only to have the flip side be the right way when the disk is flipped, i.e consumed by a 1541.
2019-06-20 12:35
Krill

Registered: Apr 2002
Posts: 1522
And why would you want to do that? :)

Give us a user story! :D
2019-06-20 12:52
oziphantom

Registered: Oct 2014
Posts: 409
Say your a publisher, and you have a popular title that needs both sides of a disk, and you have a popular game on your hands and you have 1000 orders.

So put disk in 1541, tell it to write and verify the image.
Notice that it has finished, stop what you are doing ( folding a box, stapling a manual ), open the drive, flip the disk, close the hatch, start it on the 2nd side.
Go back to what you where doing.
Wait for the 1541 to write and verify the image.

VS

Put disk in 1571 and tell it to go.
Do more stuff while you wait for it to write and verify both sides of the disk.

The 2nd case is going to be a lot more efficient, and allow them to do the orders in less time. Might make a nice little solution to package up and sell to them ;)
2019-06-20 13:12
ChristopherJam

Registered: Aug 2004
Posts: 1081
Quote: I'll add more words

The goal is to write an image with the 1571 only to have the flip side be the right way when the disk is flipped, i.e consumed by a 1541.


Probably doable. You just need to flip all the bytes, reverse the buffers, do each sector before each sector header, and place the sync marks at the end of each write instead of the start. No idea if the alignment would be correct..

Start with a custom formatter, edit in those changes, and see if it works!
2019-06-20 13:29
Krill

Registered: Apr 2002
Posts: 1522
Yeah, a lot of ifs. Might or might not work.

But if you're really going to duplicate 1000 double-sided disks, you'd probably be better off rigging something together with a PC and Kryoflux or Catweasel.
2019-06-20 14:11
Mr. SID

Registered: Jan 2003
Posts: 376
Are you going to sell the 1571 drives as part of the solution? :)
2019-06-20 14:37
soci

Registered: Sep 2003
Posts: 450
Yes it is possible to write it backward but it will not work very well.

While the two heads are physically located above each other the coils are not.

Practically this means the 2nd side head can't reach some of the lower numbered track locations.

So there will be like 4 or 5 tracks worth of misalignment unless the inaccessible lower tracks are skipped and not written.

In my opinion avoiding the side flipping won't gain much as with a bit of practice the majority of time will be spent on writing and verifying the disks.
2019-06-20 22:08
bugjam

Registered: Apr 2003
Posts: 2015
I have to say I do like the idea. Pity it seems to face a lot of obstacles.
2019-06-21 07:49
oziphantom

Registered: Oct 2014
Posts: 409
Quoting soci
Yes it is possible to write it backward but it will not work very well.

While the two heads are physically located above each other the coils are not.

Practically this means the 2nd side head can't reach some of the lower numbered track locations.

So there will be like 4 or 5 tracks worth of misalignment unless the inaccessible lower tracks are skipped and not written.

In my opinion avoiding the side flipping won't gain much as with a bit of practice the majority of time will be spent on writing and verifying the disks.


Is this why the 1571 is 35 tracks only. In that its actually 40, just it uses the inner 35 on the top side and the outer 35 on the bottom?
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