The first one I got to use seriously was a PDP-11/70, that was before switching to an IBM370 and assembly programming.
The stupidest mistake I ever made programming was forgetting to sort the data which was used to create an indexed file. Hours later, when I realised what I'd done, the program ran in under 10 minutes.
The most profitable program I wrote (from the company's point of view) was one to list all the obsolete tools so they could be sold for scrap - that one brought in £250,000 in the early 80's.
The shortest program I wrote was about 6 lines of code to read a tape created on another system and write it to one which could be read by our system.
I started to lose faith in systems programmers when one told me that, no, it was absolutely NOT possible for a COBOL program to start printing on one type of stationery and then call for another type to be mounted. It didn't matter that it was a program I'd been asked to amend it to use a third type of stationery, so it was already doing what was wanted - all I needed to know was how ! In the end I found two ways of doing it.
The first "portable" computer I used was a Kaypro - to say it was weighty is putting it mildly - solid steel casing and built to take knocks. That ran CP/M, had no hard disk, just a couple of 5.5" floppies, and ran programs to help farmers with crop plans and milk records.