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Was there ever a RX50 controller for pdp8?

Roland Huisman

Roland Huisman

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I think the title says it all. Was there ever a RX50 controller for the pdp8? I've never seen one... But the later decmates had a RX50. For the unibus there was the RUX50 controller. Since the unibus has about the same age as the omnibus I'm wondering if there was such a controller for the omnibus too. Or maybe a third party unit? Otherwise I'm wondering if it would be useful to make such a controller for the Omnibus. Maybe the decmate drivers can be used on the pdp8 as well?

Regards, Roland
 
I don’t believe I have ever seen a reference to one. However, you have read my mind about making one!

I was hoping to get your drive in the post this coming week. Unfortunately, I have to go on a business trip, so it will be next week now. I have to get the money to pay for my hobby somehow!

Dave
 
I don't remember seeing anything like that. And a third party unit would probably not have used the RX50 drive due to its incompatibility with other floppy formats. I've thought an Omnibus SCSI controller would be an interesting device and I don't remember one of those either.
 
After a little sleuthing on the net I found references to the CESI MDC8 controller for the 8/a. It is a hex width board so really only the 8/a. I've not found anything resembling a spec sheet or product description. I get the impression that it will support some hard disks and some floppy drives. Some references indicate it is a SCSI adaptor.
 
For the 8 directly, not that I can recall but the DECmate shipped with RX50, so at least on an incompatible level there was something officially.
 
DougIngraham said:
Some references indicate it is a SCSI adaptor.
Click to expand...
There's been recent discussion about a surviving instance, I think, now in Atlanta. Charles Lasner apparently did a lot of P?S8 development on an 8/A system using one. The curious bit is that the drive appears to be MFM in the photos, so apparently there are a couple of adapters involved.

The OS/8 driver is a bit of a horror. Apparently it implemented 30+ OS/8 file-systems. But OS/8 can't have any where near that many devices. So you have to generate a pile of OS/8 configurations. The first is installled on, say, the first 4 drives, and can also access file-system 5. Then another on the next set of file-systems, with another slight overlap. 8 such OS/8 configuraions could access the whole drive, but only in, say, 5 Mw sections. Copying stuff around meant multiple copy-and-reboot operations, unless you could fit the file onto a floppy or the like.

I believe P?S8 has similar issues but it's much easier, since each driver can have 8 units. So 4 drivers could cover 32 file-systems. OTOH, the file-systems can only be 0.5 Mw because of the block being 128W instead of 256W.

All in all, it should be an amazing mess.

Vince
 
Hi Vince,

SCSI and mfm? Sounds to me like a sasi interface. Xebec S1410 for example. Especially around that time. Also used in some S100 systems. Since the interface is simple I would expect that these can work in a pdp8 too.
Maybe wasting some disk space because of the 12 bit data...

Regards, Roland
 
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