Actually, I started on a SWTPC 6800 with 21k of memory and a cassette tape drive. It was only 1979.
Then, I moved up to HDOS on my Heathkit H89. Finally moved to CP/M on that.
Wow.
You and I have LIVED computer history.
:)
I had a pocket Trash-80 (Radio Shack TRS-80) with all my engineering formulas on it written in Basic. It was indispensable and was a permanent fixture in my briefcase.
Then I got an Otrona Z80 portable with CP/M on it, booting from 80K 4.5” floppies. Later had an upgrade to an 8086 motherboard and MS-DOS with 160K 4.5” floppy drives.
Wrote all my circuit modelling programs in Turbo Pascal and even used MultiPlan spread sheets.