Spelunking the places where files are not

Paul Koning paulkoning at comcast.net
Fri Mar 5 16:08:23 CST 2021

> On Mar 5, 2021, at 5:02 PM, Glen Slick via cctalk <cctalk at classiccmp.org> wrote:
> On Fri, Mar 5, 2021 at 1:46 PM Paul Koning via cctalk
> <cctalk at classiccmp.org> wrote:
>> Yes, RT11 has contiguous files.  That actually made it rather unusual.  For example, while RSTS supports contiguous files that isn't the default and because of disk fragmentation wasn't commonly used.
> On VMS you can copy files with the /CONTIGUOUS switch to specify that
> the output file must occupy contiguous physical disk blocks. Of course
> the default is /NOCONTIGUOUS.
> I vaguely remember using the /CONTIGUOUS switch to copy MDM (MicroVAX
> Diagnostic Monitor) diagnostic files from one bootable MDM disk to
> another. I forget if that is necessary for proper operation of MDM.

I like to make RSTS floppy files contiguous to avoid spending so much time going back to the directory to find the next set of file data pointers.  In RSTS, a few files have to be contiguous: run time systems and shared libraries, swap files, the system error message file, and the DECtape directory buffer file.  That's about it.  In early versions, the monitor had to be contiguous as well, but as of V6B that is no longer true (not for INIT either).

Strangely enough, in the RSTS file system there are always pointers to each file cluster, even if the file is contiguous.  It didn't dawn on me until a few weeks ago that I should have changed that -- I could have done that back around 1982 or so.  Oops.


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