27 Sep
2012
27 Sep
'12
4:56 p.m.
Re:
This application is titled "Quick filename lookup
using name hash". Based on the title, it sounded like they are doing what TRS-DOS 2.0
did back in 1978, which is putting on the disk a hash table of filenames which then refer
to directory entries. TRS-DOS did that so that it usually only needed to read two sectors
to look up a file, the HIT (Hash Index Table) sector, and the actual directory sector
containing the file's directory entry. Otherwise they might have had to read multiple
directory sectors to find the file if it existed, and all of the directory sectors if it
did not.
There's some chance that Burroughs MCP file directory mechanism may have done
something similar, back around 1972 (?). I recall MCP switching from a
(now familiar to most) one-file-per-directory system, to a
the-entire-directory-in-one-file
system at about that time. One of the claimed advantages was the ability to
find the file entry in "one or two disk reads".
But, it's long enough ago that I don't recall the details. There's a chance
that Jim Madden (UCSD Computer Center) or Don Gregory (ex-student at UCSD) might know.
Stan