Did you miss Part 2? Check it out here
Part 3: The 1970s
My Princeton days centered around an IBM 390/91 running ASP/JES3 with its little brother the 370/158, while bunches of 360/20 systems were remotely feeding in jobs from around the campuses and even as far as Colorado. (360 Model 20s were not “real” 360s – not good for much except handling card readers and line printers)
The way all the remote devices, whether RJE or interactive terminals, plugged into the mainframes was via a 2703 terminal multiplexer. Think of it as a bunch of channel-attached serial ports implemented in stone age technology. More later.
When Princeton got the VM/370 operating system on the 370/158, there were then lots of virtual machines which had to communicate with each other and the outside world with – what else – virtual decks of cards. VM came with RSCS, the Remote Spooling Communications Subsystem, which was a lot more pleasant to use than ASP and JCL, but still had to interoperate.
So that was the mid ‘70s. Starting in 1969, a little thing called the Arpanet started to happen. The Arpanet was used to connect the big computers among researchers into one network, but the way it was done was by putting all of the new networking stuff onto IMPs – Interface Message Processors. These were programmed by BBN, but the hardware was the DDP-516 minicomputer from Honeywell. So the IMP was another kind of SmartNIC or front-end processor.
Lots of history out there about the Arpanet and IMPs. But another early predecessor of the Internet was BITNET – and it all started on IBM machines running VM and RSCS. So all that punched card communication did eventually evolve into something more familiar.
By the late ‘70s I was working on UNIX under VM/370 at Amdahl (IBM 370 clone company) and writing drivers and protocols to make UNIX fit in to the IBM world. Yes, there was a virtual card reader driver. Virtual CTCAs, check. RSCS job submission, etc. But where it got really weird was with the 3705 – a “Front End Processor”.
The IBM 3705 was a programmable box – truly a Smart NIC – which could emulate and replace the old 2703 terminal mux, but was also the centerpiece of SNA – IBM’s Systems Network Architecture. They were everywhere in the IBM world by 1980 or so, and SNA was creeping in. So I figured I’d look into implementing SNA on UNIX. But the complexity of SNA utterly broke me, and ended my belief in the future of IBM mainframes!
Head over to Part 4 to keep reading.