🚀 go-pugleaf

In article <1073@mixcom.COM>, xxwwxx@mixcom.COM (Tim and Tim Company) writes:

> The QD01D is MSCP, will support *ANY* two MFM drives
> you hang on it, up to 16 heads (each?).  Drive
> sizes, etc. vary.  If you get a newer one, it
> will have a bootable routine for formatting,
> testing, configuration, etc.  The interleave
> factor is 1:1.
> 
> The nice part about it is the emulation.  It appears
> to the system as 1 or 2 RA81's, which I would imagine
> is supported by all the operating systems that support MSCP.
> 

WARNING !! The very fact that these drives are identified to the operating
system as RA81s *WILL CAUSE PROBLEMS*!!  VMS is smart about it, as are most of
the PDP-11 operating systems, but certain operating systems including most
flavors of UN*X and at least two MUMPS based operating systems I have worked on
in the past have fixed tables describing disk geometry.  In the case of MSCP
disks it uses the drive name (i.e. RA81) to determine this information.

One of the nice things about MSCP controllers is they give the operating system
the size of a disk volume in blocks.  Unfortunately, certain operating systems
that are not limited to Digital Equipment cannot bank on this capability, and
therefore have "hard wired" tables.

Usually these tables can be modified, but it still leaves you with a catch-22
if it is the disk you plan to be installing software on. 

Also, if you have two drives calling themselves "RA81" and having different
sizes, it will vastly confuse these operating systems.

This is not based on assumptions, I have personally fought through these
problems.
-- 
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  Lawrence Fisher                Internet: fisher@edwards-vax.af.mil
  Digital Equipment Corporation                         ^
  Principal Software Specialist  Currently working here | (Edwards AFB, CA)
  Specializing in Realtime       
  Disclaimer:  I don't speak for Digital or the U. S. Air Force
    "Bomb Number 20, you're out of the bomb bay again"
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