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

[Johnny Billquist]

On 2023-09-28 05:52, gah4 wrote:
> On Wednesday, September 27, 2023 at 5:55:54 PM UTC-7, Dave McGuire wrote:
>> On Wed, 27 Sep 2023 16:04:28 -0700 (PDT), gah4 wrote:
>>>>> 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.
> 
> Power bills I don't think LCM ever worried about, though maybe they should.

I run some small machines, and have had them running for over 20 years 
now. Including disks... Hello PDP-11s...

>>> 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.
>   
> Reminds me of another DEC disk, which can be used on either PDP-10 or
> byte addressed machines. The controllers are different, and can only write
> blocks with the appropriate size, which I believe is 576 bytes for the PDP-10,
> and 512 otherwise.  You can't read disk packs on the other one.

There is the RK05 which is hard sector format and have two different 
disk packs. One for 12-bit machines, with 16 sectors per track, and one 
for 16-bit machines, which have 12 sectors per track.
I think those are close to impossible to read on the wrong machine.

But apart from that, I think most DEC controllers and disks had special 
modes to read the odd stuff, but it wasn't very practical for anything 
except possibly recover data on a different system.
But it might also have been that you couldn't read the pack at all. But 
you could at least reformat it and use it on either system. (Talking 
mostly about -16, -32 and -36 bit systems here.)

   Johnny