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[Sam Varshavchik]

Giacomo Magnini writes:

> Sam Varshavchik ha scritto:
> 
>> My old Atari ST computer used FAT on floppies. I think Amiga did to.
>> No.  Amiga used a very funny filesystem for their floppies.
> 
> Maybe AFFS is funny by today's standards, but at the time it was much 
> more advanced than fat:
> - long filenames
> - more data on a floppy (880K instead of 720K)

That had nothing to do with the filesystem format per se.  The additional 
room was obtaining by completely eliminating inter-sector gaps. 
FAT-formatted floppies have gaps placed in-between sectors on a track, in 
order to take into account the setup time needed to place the R/W head into 
write mode, and to take into account variations in recording speeds between 
different drives.

Amiga floppies didn't have inter-sector gaps, which is where the additional 
storage came from.  Amiga floppies were read and written a whole track at a 
time.

> - much faster (even for todays standard: ever tried formatting a floppy 
> under Win?)

You've got to be kidding.  Do you even recall the experience of trying to 
open a folder from a floppy, in Workbench?  Amiga's filesystem used hashed 
directories.  Reading a directory meant, essentially, traversing hash chains 
all over the floppy.  One block per file.  Meaning that each directory entry 
usually required a floppy head seek.

Each file block itself had a header.  I think that each 512-byte block had 
only 488 bytes of file data, the rest was the header.  I forgot the exact 
byte count, I think it was 488.  That didn't really matter much with 
floppies, but that meant that you couldn't exactly use DMA to read/write 
data to/from a hard drive.  An intermediate buffer had to be used for 
processing the header and reading/writing it from the hear drive.

A “Fast File System” was added to a later revision of AmigaOS, which 
basically removed headers from data blocks, allowing for much faster DMA 
to/from hard drives.


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