[Info-vax] Anyone interested in another public access system

[Bill Gunshannon]

In article <gs2jq1$c44$3 at naig.caltech.edu>,
	glen herrmannsfeldt <gah at ugcs.caltech.edu> writes:
> 
> In the days of small memory, caching files in memory was
> not possible.  The RT-11 file system allocates contiguously.
> As I remember, the first file open is at the beginning of the largest
> free area.  When another file is open, it is either at the
> beginning of another large free area, or at the middle of the
> free area being used by the previously opened file.  

Not sure of this was a DEC thing or just the way it was done in
those days, but the exact same was true of UCSD-Pascal running
on the PDP-11.  If one wanted to have ore than one file open
for writting one had to do the equivalent of an "un-squeeze".
You had to make sure there were two "holes" on the disk large
enough to hold all of the files you were expecting to write.
Otherwise, you were headed for a "No space on disk" error.
And a lot of frustration.

> 
> For OS/360, there is the SPACE parameter of the DD statement
> indicating the expected size for the data set.  The initial
> allocation is done in up to four extents (contiguous groups
> of tracks).  If the file keeps growing, secondary allocation
> is done up to a total of 16 extents.
> 
> The OS/360 solution for the many small files problem,
> (such as macro libraries) was the PDS, Partitioned Data Set,
> often called a library.  A PDS is allocated in disk tracks
> (as are other data sets) and then members written into the PDS,
> similar to the library files of, I believe, VMS.  Members
> are stored contiguously at the end requiring COMPRESS to
> recover the space used by deleted members.  
> 
> I would expect all systems from the time of small memory
> to have some way to efficiently store small files and
> access them.

You would expect so.  MSDOS being the odd man out.  Ever create a
disk with a whole lot of small files on it? (Like the source for
MS-Kermit!)

bill


-- 
Bill Gunshannon          |  de-moc-ra-cy (di mok' ra see) n.  Three wolves
billg999 at cs.scranton.edu |  and a sheep voting on what's for dinner.
University of Scranton   |
Scranton, Pennsylvania   |         #include <std.disclaimer.h>