Royal McBee / LGP-30
The LGP-30 [Librascope General Purpose-30] is considered by many including me to have been the first minicomputer. It was a vacuum tube machine with a rotating drum memory, 32 bit word length, 4096 words of memory, an accumulator and a couple more registers for program control. There were 139 tubes. It used hexadecimal notation and a Friden Flexowriter for I/O. The only options were a high speed photo reader and high speed paper tape punch. They ran at 60 characters per second input and 20 CPS output to/from paper tape. The machine language instruction set consisted of 16 commands, the most significant one being a "Return Jump" which was a way of jumping to a subroutine and marking the point of the jump plus 1 so that you could easily return to the point where you started and continue. No other computer had such a command, not even the biggies of the time like the IBM 704 or the Univac II. There was a single pass compiler for it and a lot of other very advanced software. It was a lot of fun and I darned near lost my happy home over it more than once.
On my birthday in 1961 I got called in to Johns Hopkins to fix one of their computers belonging to a couple of x-ray crystallographers. It was a Saturday, and I kept calling my wife all day to tell her I'd be home "soon." She fixed a beautiful steak dinner, sent the kids to the neighbors for the night, put on a sexy nighty and robe left over from the honeymoon and waited ---- and waited and waited. When I finally walked in at about midnight she pointed to my cold steak, Birthday cake with several pieces missing, kissed me on the cheek still looking beautiful in her nighty and robe, walked into the bedroom, put on her flannel PJs and went to bed! Oh well, I had fixed the damn machine and those two professors still remembered me the last time I met someone who saw them at a meeting, in 1978. Barb forgave me and eventually learned to live with my workaholic ways.
I graduated to the successor to the LGP-30, the RPC-4000, a much bigger and faster computer. It was still a 32 bit drum machine but had 8192 words of memory and much better I/O (higher speed paper tape and typewriter). I still have the reference manual from that machine. It is the oldest one I have. Over the next several years I worked on at least eight more computers in price from $90,000 to about a half million and learned a lot about computers in the process, gained a good name for myself that was known nationally and made friends with a lot of millionaires.