On 29/03/2016 14:24, John Rumm wrote:
FAT was basically just a formalisation of what was inherited from
CP/M... it was not until MS hired a patent lawyer with the intention of
finding new way to monetise old intellectual property, that FAT was even
really acknowledged as being an item rather than just a bit of
technology that loads of people used. It main goal was simplicity and
lightweight implementation - as was demanded by the needs of the time.

This turns out not to be the case.

CP/M discs had a set of directory entries for the files. Each entry had
a few (8?) clusters described in it; if the file was big it had multiple
directory entries.

One of the boot up tasks for CP/M was to read all the entries, and build
a free space bitmap in memory. No need for chkdsk to find lost bits.

Andy