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

[P. Sture]

In article <gs5ird$af3$2 at naig.caltech.edu>,
 glen herrmannsfeldt <gah at ugcs.caltech.edu> wrote:

> P. Sture <paul.sture.nospam at hispeed.ch> wrote:
> (snip, I wrote)
>  
> >> 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.  
>  
> > I can't remember whether it was a DIBOL specific thing, but on the RT-11 
> > systems I worked with when opening a sequential file for output, the 
> > allocation made was half of that free space, truncating at file close. 
> > Therefore if more than one sequential output file was opened at the same 
> > time, you _would_ get fragmentation. When an output file became full, 
> > the system would ask you for a continuation file specification, then 
> > continue.
> 
> I thought the first file was at the beginning, and the second
> started half way.  I forget that it only gave half if there was
> only one file.
> 

We are both right - the second file starting half way was the result of 
the first file reserving half the free space.

> I believe that subsequent files divide the last one in half.
> (1/2, 1/4, 1/8, ...).

I'm not sure, but I always thought of it as dividing the remaining free 
space by half. IIRC, this could be demonstrated by aiming a continuation 
file at a different disk.

Happy days though; the beauty of that system when compared to mainframes 
was its simplicity, which allowed us the time to concentrate on the 
business side of things.

-- 
Paul Sture