Re: ProDOS misc. questions

[dempson@actrix.gen.nz (David Empson)]

In article <1921.678.uupcb@yob.com>, jeff.brielmaier@yob.com (Jeff
Brielmaier) wrote:

>By defination, the Volume_Directory and the Volume_Bit_Map MUST be contiguous.

No they don't.  The only fixed blocks on a ProDOS volume are block 0
(boot) and block 2 (key block of root directory).  Everything else is
pointed to by the root directory.

In theory, the individual blocks of the root directory can be scattered. 
The bitmap blocks (if there are more than one) must be contiguous, but
they don't have to be adjacent to the root directory.

It doesn't make much sense to have non-contiguous root directory and
bitmap (what would be gained?), but the file system doesn't prevent it. 
(The operating system might not handle it properly.)

The only useful feature I can think of in this area is varying the number
of blocks allocated to the root directory (hence the number of files that
can be stored there).

>I had tried to split the Volume_Directory (years ago), but must utilities 
>programs barfed

Poorly written programs.  They would probably also break on a disk which
had fewer blocks than expected in the root directory.

(Volume Repair utilities obviously cannot be expected to be psychic - they
start from a standard definition of a "good" disk, and if you have
something unusual then they are bound to get confused.)

>and the files on the "extension" suffered from slower access times due to
>the drive heads having to 'bounce' around the drive.

Yet another reason not to try anything weird.

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand