[Info-vax] Assistance needed!! working RM05 drive and VAX needed for proje

[Dave McGuire]

On Wed, 27 Sep 2023 16:04:28 -0700 (PDT), gah4 wrote:
> When it was open, the museum computers were running 24/7.
> Even when they were new, those drives were never expected to do that. 
> Systems I remember, had a maintenance time every morning. And disks were
> often backed up every day.

  Some of their exhibit machines were running 24/7, but very few...not 
all.  And those that did (the IBM 4331 comes to mind) ran on emulated 
disks and other peripherals.

> At some point, though, it isn't obvious what emulated means.
> 
> I a MicroVAX an emulation of the 11/780?

  Let's not rehash the old argument of whether, say, a microcoded 
implementation is an emulation or not, as fun of a Usenet thread that it 
may (yet again) be.  In this context we're talking about real hardware 
being replaced by, i.e., Raspberry Pis, rather than repairing and 
maintaining the real hardware.

  Note well that I'm not talking trash about LCM here.  I respected the 
institution and its staff while they were around.  One of their former 
staffers works with us now.  But their approach was just very different 
from ours.

  But since you mentioned it, you seem to be the type of person who knows 
about the differences between the MicroVAX (pick your flavor) and the 
11/780.  Which floating point formats are implemented or not (two 
different versions of the KD32!) etc etc. ;)

>> > Keeping old disk drives running is much harder than old CPUs.
> 
>> It is, but we do it at LSSM. It's not like it's impossible.
>  
> Running continuously for 20 years might be, though.

  Nobody in their right mind would do that now.  Not only is it pointless 
(who's going to show up at 3AM to sit in front of a machine?) but there 
are power bills to be paid, fire concerns, etc.

> One way that LCM does floppy disks, is to make a bit image backup.  That
> is, not decode the bits, just record where they are.
> That works even if it is an unusual low-level format.

  It's pretty brute-force, but yes, that's a workable approach.  And it 
also means people who know nothing about the computers can run the 
backups.

> That might be the best way to read old RM05 packs, too.

  It may be.  Media recovery is mostly a solved problem for more common 
formats.

                -Dave

-- 
Dave McGuire
Large Scale Systems Museum
Pittsburgh, PA USA