>I think you'll find these are the same creature, but in two different modes
>of operation.

They are very similar.

>Hopefully I've remembered this correctly:

>What has been done is to remove the drive number from the disc address,
>which provides an extra 3 bits, and increases the possible disc size to 4GB.
>However, because of potential problems with disc addresses with the top bit
>set (the original FileCore code didn't need to worry about signed disc
>addresses), Acorn suggested caution with discs above 2GB.  Not sure if that
>was just for the Clan beta, or in general.

>There's also support for "big discs", where the disc address is in multiples
>of (I think) the LFAU, not bytes (LFAU is Large File Allocation Unit).  This
>allows for enormous (by today's standards anyway) discs, though the bigger
>the LFAU, the more space is wasted by "rounding up" of file sizes.  FileCore
>can put small files into spare space at the end of LFAUs, but this can only
>help up to a point.

Not quite correct.

The change that has been made was to change from using the byte offset
into the disc and instead use the sector offset into the disc.  This means
that the maximum size of the disc is sector_size*(2^29) bytes.

This is the case for FileCore in 3.60, the Clan release, and RISC OS 3.70.

A further change to stop sharing become useless was introduced at the same
time; this generally only affects discs larger than 2G bytes.

Simon Proven


-- 
Simon Proven - Software Engineer, Acorn Risc Technologies
Acorn Computer Group Plc, Acorn House, 645 Newmarket Road, Cambridge, CB5 8PB