On Tue, Feb 23, 2021 at 9:53 PM Chris Zach via cctalk <cctalk at classiccmp.org> wrote: I started on an 11/750 in 1984. They are fantastic little machines. If you only have 3-4 users on them, they are quite peppy. The module map indicates an SI 9400 interface (CMI card to an SI 9xxx SMD disk box) and an L0007, which is an RH750 MASSBUS adapter. Those slots appear to be populated with _something_ in the photo. There _might_ be a MASSBUS connector at the lower-right of the I/O bulkhead. The CPU area seems to show an FP750 Floating Point accelerator installed in slot 1. It also appears there are a couple of cards in the memory area in slots 6 and 8. What I don't know, since I didn't have one, is how you load up a machine with an L0022 14MB memory controller, but it's _possible_ we are looking at 4x 1MB + 2x 4MB (full boat). It also appears that the two DZ11s may still be installed, but the TC-131 might be missing. Indeed you did, well an M8750 anyway. ;-) Cheers, -ethan

On 2/23/21 10:57 PM, Ethan Dicks via cctalk wrote: At least until one of them fires up Eunice or the Ada Compiler. :-) 750 was my first VAX and first VMS machine, too. bill

Sort of. MASSBUS was a very overpriced and to be honest weird system that DEC developed in an attempt to be like IBM and charge very high markups for generic peripherals. While it did support a variety of interface formats (I don't think the RS03 and 04 were SMD, and I know the RP07 was *not* SMD) the industry quickly centered on SMD and that was that. Yes, the TM02 and TM03 formatters allowed MASSBUS to connect to Pertec drives, but I don't think you could run a tape drive and a disk drive on the same MASSBUS channel anyway. Wonder why, technically the MASSBUS cable is just an extension of the Unibus, so it shouldn't matter much what combination of cables you used. Maybe they just wrote different drivers or something. I have heard that the difference between what comes out of a MBA (which is huge, several quad height boards in an interface box) and true SMD is the inversion of some differential signals. Whatever it is the changes to a 9762 were very minimal, probably just one of the cards in the card cage. It's quite possible there is no difference, I'll leave that to someone else. My guess is they removed the TM03 formatter from the TU81 and just put in a SDI formatter which was nothing more than yet another closed source version of a Pertec formatter. Maybe DEC lost the contractor who built MASSBUS cables as they were better used to tie ships to a dock. (Yes, I did use a MASSBUS cable to tow a car once. Worked fine) I still have an RM80 drive in my house here, I fire it up every 5 years or so. Mostly for when I get my Decsystem/20 back together. It has the RM80 personality module which is the difference between the R80 and RM80. To be honest I'd bet that one could put an RA81 personality module into it and make an RA80 drive.... Far more interesting would be to see if one could put the RM80 personality module into an RA81 drive and turn that into a 456mb MASSBUS drive. THAT would be interesting.... C

On 2021-02-24 11:06 a.m., Jon Elson via cctalk wrote: Actually the RM05 was a 9766 - the 9762 was an RM03 when DEC re-packaged it

I have two RP07s sitting on the upper mezanine here that were left behind by the former tennant of the building my shop is in.

I do, but I don't care enough about them to try. I just want them gone. Bring your own fork lift, the battery in mine is dead and they are 15 feet up.

Overpriced? Compared to what? SMD didn't appear until later; I know Massbus existed in 1974, perhaps earlier. What else would do the job back then? Electrically it works. I believe at least one system/OS supports this; TOPS-10 perhaps? But most operating systems do not, and yes, that would be a driver issue. Similarly, not all OS support RS03/04 and RM/RP on the same Massbus (RSTS doesn't for example). Meanwhile, speaking of the RP07: DEC never supported that on any PDP-11, but it actually works just fine on the high performance Massbus of the 11/70. In the RSTS group we had one on the big 11/70 system ("ARK" because at one point it had "two of everything"). So RSTS/E will happily drive such a device, if you can manage to power it up. :-) I think IBM's "bus and tag" 360 channel cables are even thicker than a Massbus cable. Yes, but you'd need some driver work, since Massbus disk drivers have to deal with the actual drive topology. So you'd have to define a Massbus ID value for "RM81" and pick the appropriate sector/head/cylinder count. Depending on the OS this may be fairly easy or not so easy. I know how to do it in RSTS (at the source level -- doing it by patches might also be doable). paul

I know most DEC OS don't support this but I'm pretty sure that at least one of them does. Not sure which. A given Massbus can only do one transfer at a time, so yes, a tape transfer in progress would mean you can't start a disk transfer (though you can start the seek). For that matter, if one disk is transfering another can't start either. So if you want max throughput, you want to spread the disks over several massbus adapters, and keep the tape separate. But if you need lots of disk space, you may have to put tape and disk on the same Massbus since any given system has a limit on Massbus adapters (4 for the PDP-11/70?) and unit numbers are 3 bits. For PDP-11 systems, not likely to be an issue. For mainframe (PDP-10), it might be. I know mainframe systems at times had dozens of disk drives. One I used (CDC not DEC) had 22 RP04 class drives. paul