Re: Copying Mac MFS disks on an Apple II

["Charlie" <charlied@NOSPAMbboard.com>]

"Bill Garber" <willy46pa@comcast.net> wrote in message
u3mdnYVff7ZoAMuiXTWJjw@comcast.com">news:u3mdnYVff7ZoAMuiXTWJjw@comcast.com...
>
> "Charlie" <charlied@NOSPAMbboard.com> wrote in message
> bj5u080m41@enews3.newsguy.com">news:bj5u080m41@enews3.newsguy.com...
> >
> > "Greg Buchner" <apple22@mn.rr.com> wrote in message
> > apple22-A39589.22123102092003@apollo-ge0.rdc-kc.rr.com">news:apple22-A39589.22123102092003@apollo-ge0.rdc-kc.rr.com...
> > > In article <acdalv4olv4h1ajrgdhr0njafd5gv2tum6@4ax.com>,
> > >  Jeff Blakeney <CUTjblakeney@syndicomm.com> wrote:
> > >
> > > > On Tue, 02 Sep 2003 13:01:00 GMT, "M. Pender" <mpender@hotmail.com>
> > > > wrote:
> > > >
> > > > >IIRC Mac HFS disk blocks are not the same size as ProDos disk blocks;
> > there
> > > > >are a few extra bytes thrown.  I doubt that the 512 byte ProDos
> blocks
> > will
> > > > >be very appealing to the Mac.
> > > >
> > > > ProDOS and HFS both used fixed block sizes of 512 byte blocks.  HFS+
> > > > supports variable block sizes but I'm almost positive the smallest
> > > > size they can be is 512 bytes and they must contain a number of bytes
> > > > that is a power of 2 (ie. 512, 1024, 2048).
> > >
> > > (I hope I've got all of this right...)
> > >
> > > Actually it's slightly more complicated.  You have to deal with physical
> > > blocks (the actual blocks on the hard drive, which are almost always 512
> > > bytes) and logical blocks, which can vary in multiples of 512 bytes
> > > (unless the phsysical blocks on the HD are different).
> > >
> > > ProDOS supports only 512 byte logical blocks so they map 1:1 to the HD,
> > > 65536 blocks to the volume.
> > >
> >
> > One minor quibble:
> >
> > I believe ProDOS supports 65535 blocks to the volume, not 65536.
> >
> > Charlie
>
> No charlie, 65536=0 thru 65535=32,768k=32mb

Well, Bill, ProDOS volumes contain a word (two bytes) at a location in the
Volume Directory Header ($29 byte offset from the beginning).  This word
contains "the total number of blocks on the volume" (Apple's definition).  As
you know the largest value you can fit into a word is $FFFF (65535).  A quick
check of a 5.25" ProDOS disk will show that word to contain $118 (280) so the
number is NOT zero based.
I do admit that I have never actually created a 32 Mb volume on a real Apple II
to see what number is found in that location but I have always been to the
understanding that the largest volume that can be created under ProDOS is
32Mb - 512 bytes.

Charlie