I too started on micros way back in 1980, my first commercial project (as a contractor) being for a double glazing company in Ipswich on a floppy-based TRS-80 running TRSDOS. At the time, I was a programmer at the EADT on PDP-11s and moonlighting!
At that time, I ran a few PCs running CP/M, we replaced the TRS80 with a Z80 CP/M machine with a hard disk, 5meg I think, and I bought myself, at *huge* expense, an Apricot Xi10 with 984K memory which ran DOS 2.11
I then went to Peachtree in Maidenhead, and worked, in secret, on the IBMPC, which was announced later that year (1981) in November at the Which Computer show. Did a contract for Marley Floors in Kent where they ran MP/M on Televideo kit which supported 16 users and had a *massive* 40meg of disk space! Leapfrogged to and from CP/M and DOS-based PCs to VMS on the Vax for a few years, and ran my first PC Unix in about 1990. surprised not to hear it mentioned here yet: Minix. It was hard work, IIRC...
Finally started with Linux in oh, 1998(?) with SuSE 5.3 and haven't looked back. I still use 'Doze for some things, many of my customers do so I have to, but for servers, it's Linux all the way...
Cheers, Laurie.