Sinclair ZX81, purchased as a kit and assembled by myself, since I was too poor to get anything else or even get it assembled (which was $50 extra then). It even worked, but had some intermittent problems, so I eventually ended up getting it traded for a factory-assembled replacement for just the postage cost. Later put a massive 64k memory expansion on it and moved on to Z80 asm when BASIC lost its thrill.

Dang but that brings back really old memories! Back from Vietnam and was assigned the MARES-FORSTAT operator on an IBM 360. Yup! Used punch cards for data entry. If it crashed (not very often), had a manual to set switches so it would read the paper tape to boot up with.

My first computer was my own brain, I added external storage by learning to write.
My second computer was a slide rule, and then an abacus, may be the other way around.
This question is ill formed.
The first electronic computer I used was a Farranti Pegasus. Valves (tubes) and magnetic core. The first electronic computer I owned was home built from parts sourced from the junk stores on the Tottenham court road in the late 60s early 70s. I had to pre load the meter with a lot of 2 shilling coins to get it to boot strap.

My first computer was a Heathkit H89 all in one. It was a Z80 chip 8 mhz, with 48k of ram. Storage was on a single 100k 5 & 1/4" floppy disk. I had DOS and CPM for operating systems. Cant remember the versions. I just recently got rid of my D0S 6.0 disk set of 6 disks. and my Win3.0 version. And yeah that makes me old. The modem that I got later to get on the internet was a 300 baud super fast dialup. I was also a member of the HUG (houston user group), and they had a server to get on the net so my service was with them. My first Linux was Red Hat 7.0.

TI 57

IBM PC, 286, MS-DOS 4.01, early 90s

A 386 from the back of a friend's closet in 2000 unless you count my Cidco Mailstation or don't start counting until I plunked down $200 for my dear departed Garetway P-166 with 32 MB of RAM and a 1.5 gig hard drive that came preinstalled with Win98, M$Office 2000, and Gator https://what-is-what.com/what_is/gator.html after the anthrax scare following 9/11 dragged me kicking and screaming off of my portable manual typewriter.

She absolutely FLEW on D*SmallLinux a few short years later, especially after I maxed out her RAM. Everybody was disgusted with my absurd attachment to this piece of old iron until she finally bit the dust due to a power surge and stupidity on my part.

May she rest in pieces. A few of them are still in the back of my closet even though others had to go to eWaste.

My first (own) computer was a Advance 86b PC from Ferranti, IBM PC compatible, with dual drive (5.25") floppy and 256 KB of RAM. It had NO harddisk controller and a built-in (on the motherboard) CGA video adaptor (and it DID have ROM Basic like the real IBM PC.
I used it with an amber (monochrome) monitor and a Star matrix printer.
This was in 1984 and it survived about 4 years when the floppy controller gave up.

PS: it was running MS-Dos 2.11
Here is an image for that computer on wikipedia en.wikipedia.org/wiki/Advance_86