Simplest (practical) file system?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Jul 27 14:35:38 2003

> This sounds just about right, vintage-wise!
>
> Ok, so once you have a hole, do you only recover that disk space by
> SQUEEZEing the disk?
>
> I think RT-11 works this way, at least I recall the SQUEEZE command

Yep.

> making the disk free space
> larger.

The HP LIF disk format works like this too.

>
> Is a FAT needed for this, or is there a simple way to calculate this on
> the fly?

The LIF directory just stores the starting block and length for each
file. The directory is also stored in ascending order, so from the
staring blocks of 2 adjacent files in the directory, and the length of
the first one, you can work out if there's any space between them, and
how big that space is.

When a file is deleted, its directory entry is changed to indicate that
the file no longer exists, If a shorter file is then stored on the disk,
then the directory entry is changed again for the new file. THis then
leaves some unused blocks on the disk which can't be used becuase there's
no way to create a directory entry in the right place in the directory.

-tony
Received on Sun Jul 27 2003 - 14:35:38 BST