70's computers

On 10/25/2018 02:24 PM, allison via cctalk wrote: Yes, and that's where my 32-bit 2903 project started to bog down. I knew some people, OS security was a total joke, so I COULD have just stolen OS 360 MVT, but REALLY, who would do that to themselves? I had a few more bits of logic to wire in, to make a 256-way branch from the OP-code field of the instruction register to decode instructions, and from the register fields of the instruction register to OR into the register address. Then, I had to write the microcode. I'd done some small test bits of microcode, including the multiply, and that worked. (IIRC, the 2903 has an extra shift register, so it can do the multiply step in one CPU cycle, the 2901 takes 2.) Well, after that, I had a big decision to make. Should the memory be on the system bus, like PDP-11 and VAX, or part of the CPU, like IBM-360 and PDP-10? Then, I had to get memory wired to the bit slice system, and then build peripheral controllers. I had a very rough concept scratched up, about 30 chips to make a microcoded 16-bit machine, using fast EPROMS for the control store. A SCSI interface would be pretty trivial, but a read-after-write mag tape control and an 8-channel serial multiplexer would be much more complicated project. THEN, the big stuff would come, I'd need an OS and language compilers. I could probably whip up a version of CP/M with hierarchical directories and time/date stamps, and maybe a simple editor, but the WHOLE REASON for this project was to move up to modern high-level languages. And, I had badly underestimated how difficult that might become. One scheme might be to start with my CP/M-like OS, and build a wrapper program that would allow me to run OS-360 compilers and linkers with whatever object libraries they needed, and then use them to compile something more to my liking like Pascal. But, it was all looking like a LOT of work. So, I managed to clone a Nat. Semi 32016 system and got it running, but it was amazingly slow. I suspect that my kluged memory interface was not fully optimal, but even the original that I copied was pretty slow. Then, I spent BIG BUCKS to buy a uVAX-II CPU board certainly fast, almost the speed of the VAX-780's I used at work, and ALL MINE! So, that's my story. Jon