🚀 go-pugleaf

In article <1316@maytag.waterloo.edu>, dmurdoch@watstat.waterloo.edu (Duncan Murdoch) writes:
> In article <25B49A6D.23757@maccs.dcss.mcmaster.ca> cs4g6ag@maccs.dcss.mcmaster.ca (Stephen M. Dunn) writes:
> >   Yup, all the administrative stuff (except for subdirectories) is
> >at the front of a DOS disk - the FAT and the root directory, primarily.
> >This is why it makes sense on DOS to have the most important files at the
> >front of the disk.
> 
> No, all the administrative stuff is at the front of a DOS _partition_.  It 
> sounds (from the original post, about putting it in the middle of the disk)
> as though it would be worthwhile setting up the most heavily used partition
> about halfway through a disk, so that its FAT ends up in the middle tracks.

It really doesn't make much difference whether you talk about putting the
most heavily used partition in the middle of the disk, or the administrative
overhead within each partition into the middle of each partition.  Both
techniques will tend to reduce head movement time;  in fact, a strong
argument could be made that they are essentially the _same_ technique, just
employed at different levels of the disk structure.

An optimal file placement strategy is difficult and unique to each user;
however in the absence of other information, placing things like the 
administrative overhead for each partition in the middle of the partition
means that the heads have to move at most 1/2 the width of the partition
in order to get from the directory/FAT area to the file being opened/closed/
whatever;  the expected distance will usually be significantly shorter (and 
will depend on file placement and frequency of reference).  Likewise, if
a program was using files in the most-heavily-used partition, and then
opened a file in another partition, the expected head movement would usually
be smaller if the most-heavily-used partition were in the middle of the disk.

Most high-end operating systems use techniques like this, to squeeze as
much as possible out of the disks.  The effect is somewhat incremental
compared to defragmenting a disk drive or careful design of the on-disk
data structures, but it is quite real and is a fairly easy way of increasing
the performance of just about _any_ file system design.  For what it's worth
OS/2's new HPFS (High Performance File System) uses such techniques, amoung
others, to achieve its performance.

							Bruce C. Wright