Re: Disk Images and Sparse Files.

[David.Empson@bbs.actrix.gen.nz]

In article <1992Nov19.220015.18453@fawlty.towers.oz.au> johnmac@fawlty.towers.oz.au (John MacLean) writes:
> The subject says it all. Anyway, here they are:
> 
> 1) Can Copy 2 Plus (or any other common //e program) create a file which
> is a "disk image" of a 5.25" disk.

Yes, but only Copy II+ version 7.x.  They removed the feature in 8.0
and later, which was a great pity.

> 2) Does the program chosen in 1) create sparse files or non-sparse files,
> in cases where large numbers of sectors are zero filled.

I haven't looked closely enough, but my guess is that it wouldn't be
sparse.

> 3) Whats the best way to create a non-sparse file on the GS, using the
> ProDOS FST?

You can't.  Whenever the ProDOS FST sees that a block of zeros is to
be written it always sparses it out.  If you write nonzero data into
the block, SET_MARK back to it and write zeros, the block will be
deallocated.

To convert a file to sparse using the ProDOS FST, simply copy it.  The
only way to make it non-sparse again would be to use a ProDOS-8 based
copy program that writes out zero blocks if the original file was
sparse.
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand