Re: Reformatting 720 KB IBM diskettes

[david@uow.edu.au (David Wilson)]

Simon Williams <DON'Temail@luddite.ca> writes:
>   I just picked up a box of 720KB double density 3.5" floppies which
>came formatted for IBM. So I reformatted them with CopyII+ and ended up
>with 800KB prodos...
>   I couldn't find a single point in which they differ *physically* from
>800KB diskettes I have, are they in fact the same?

Yes. Both 720KB and 800KB 3.5" diskettes are DSDD.

>   My guess is that they are the same thing but that IBM's formatting
>has more overhead than Apple's.

It is not the formatting (GCR vs MFM) as such but the ZBR (Zone-Bit-Recording)
the 800KB drive uses. There are 5 zones holding 12/11/10/9/8 sectors/track with
each zone being 16 tracks wide. Without this the Apple format would only hold 640KB.

>   C2+ asked if I would like to use High Speed Interleave... I didn't. 
>Does anyone think I should have??? I understand what this means, but not
>how it applies to Apple II's.

800KB disks use 2:1 or 4:1 interleave. If you are using GS/OS and Apple 3.5
drives use 2:1. If you are using ProDOS 8 or UniDisk 3.5 drives use 4:1.
High Speed is 2:1.
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia