[Info-vax] VMS defragmenters

[Bob Koehler]

In article <gs878m$6lf$5 at naig.caltech.edu>, glen herrmannsfeldt <gah at ugcs.caltech.edu> writes:
> 
> I don't know about VMS, but IBM's MVS has an Unmovable attribute
> for files, mostly for ones that have absolute disk block addresses
> in them.  They at least did that for ISAM files.  

   I could never understand why IBM used absolute block addresses in
   its ISAM, or why some MS-DOS DBMS vendors did the same.  VMS
   keyed-indexed files don't.  C-ISAM and D-ISAM don't.

   Having written some low level file access stuff with relative
   addresses I never saw any advantage in using absolute addresses.

   But I have had a similar problem with someone who created a shareable
   writeable image and then used a LINKer BASE statement so he could
   store addresses in it.  This broke big time for VMS 6.0 and it was
   trivial to recode to relative addresses and remove the BASE
   statement.