First OS: Win 95 (As a wee lad). First Linux: early lubuntu and backtrack that I used in college around 08-09.

TOS

First OS: DOS 4.something on dad's PCXT clone.

First Linux: Kurumin Linux

Slackware 1.0, dann S.u.S.E

Zx spectrum --> msx-dos --> ms-dos --dr-dos --> win95 --> Suse (before it was bought by novell) --> win98 --> debian

Windows 7 -> Windows 10 -> Kubuntu -> Linux Mint -> Nobara -> Pop!_OS -> OpenSUSE TumbleWeed -> EndeavourOS

First OS: MS-DOS 5

First Linux (many years later): Yellow Dog on one of those dome-shaped iMacs with the PPC chips

Windows → Mint → Windows → Void → NixOS

Reading the comments I want to say I feel old (25y) but compared to others I feel like a gen alpha

I came late in the tech world. I started with Windows XP

And my first distro was Ubuntu 10.10 till Ubuntu 17.10. Now I just hop from distro to distro. Right now using Pop!_OS for a year now.

First OS: Windows ME (shudders)

First Linux distro: Some random one designed to run on Netbooks (Couldn't get wireless to work if I remember correctly)

First time --> Basic (???)(Amstrad CPC464) --> MS DOS Windows --> 3.11 (yes, 3.11)-> W95 -> W98 -> Win Me -> Win XP -> Win 7 -> Win 10 (only for some games) GNU/Linux --> (2013) Mint -> Debian ->Manjaro (2-3 days) -> POPos (2-3 days) -> Mint -> Nobara --> Fedora (last Year)

Windows XP on a laptop. Then Windows 7 on a new laptop. After that, Windows 10 and Windows 11 on desktop and another new laptop.

Tried Debian on my laptop. Later, switched completely to Linux Mint on desktop. Distro-hopped to Kubuntu (KDE Plasma). Wanted to get Plasma 6 immediately after release, so I installed EndeavourOS on my desktop and laptop.

Now switched to pure Arch Linux on my desktop PC, didn't boot Windows on any of my private PCs for months (no dual boot, only GPU passthrough VM).

Windows 3.1, 98SE, XP, 7, 8.1, 10 and now 11.

I did once use Ubuntu for a few weeks but this was after someone at school goaded me into acquiring a copy of Norton PartitionMagic to try and merge two awkwardly partitioned drives on my computer, which then nuked my C:\ partition. I didn't have a backup copy of Windows XP to reinstall from so I had to go open source.

Needless to say, we didn't remain friends after that.

Apple ProDOS yo! Then System 6 and on.

First Linux was a Debian disto packaged with Linux for Dummies somewhere in the late 90s/early 00s.

First os: technically the Wii's os and android

First Linux: Ubuntu 16.04 (I remember it like it was yesterday 🥲)

First OS was DOS, though my parents used a computer with Windows 3.1 on it before we got the dos box.

Excluding Damn Small Linux, first real Linux was Mandrake 9.2 (download edition).

My first OS was whatever ran on a Commodore 64. I guess the Commodore kernel and Basic?

My first distro was whatever version of Fedora was current in the fall of 2008. I'd gone to university that year and my laptop crapped out. Couldn't afford a legit Windows license at the time to replace it, and I'm pretty sure I just remembered that Red Hat was a thing and found Fedora that way. One thumb drive and 16 years later, still using linux, so I guess that was about the only good thing to come from my abortive first attempt at higher education.

Personal computer? Windows 3, I believe, but worked on computer earlier than that by a couple of years - I'm not sure what OS, it was maintained by this old guy named, no kidding, Mr. Fox. Had a rudimentary spreadsheet program.

First OS: I think it was Windows 98. I have then gone through XP, Vista, 7 and staying at 10 for as long as i can.

First Linux distro: Ubuntu 10.04 or 10.10 don't remember clearly but it certainly was before GNOME 3 and in a VM. From then i have also run Fedora, Debian and most recently Linux Mint and Pop! OS in VMs as well. Maybe one day i finally set up a dual boot...

Mac OS 7. By the mid-2000s, I adopted Arch Linux after looking into some other Linux distributions.

DR-DOS

On my first PC it was DOS 2.0, but before that I had a Vic-20, then a Commodore 64.

MSX, some version of MS-DOS, DR-DOS, Windows 3.0, 3.11, Slackware 3.0, Windows 95,98,NT,XP,7, CentOS, and now, MacOS.

At work, Windows XP,7 and 10, and several versions and flavors of RHEL.

Well, this sets a new level of recent here judging by the comments.

Desktop OS: Linux Mint 20 MATE. Yep, that's right. I only got my first proper computer in 2020.
Thankfully, I had to install the OS myself, which was of course preceded by choosing an OS.
I had Windows 10 on that laptop for 2 days which served me to compare different OSs and burn the install DVD. I had no flash drives, and just dug out one old DVD-RW. OK, I'll be honest, hearing about Linux first I was searching for "just Linux", pure Linux, not derivatives. Oh well, GNU+Linux copypasta actually being helpful.

Alright, but why did I "have" to install an OS if I got it with Windows? It was used. I did reset it, but even though it was my first proper PC, I had no lack of paranoia. I thought that someone before me could have put spyware on that.
And I was right. Not the way I thought, but I was. That someone was Microsoft.

Apple DOS Edit: Apple ProDOS
First Linux, I'm not sure anymore. Whatever was prevalent in the mid 2000s.

Commodore64 for first OS, taught myself to type and then taught myself BASIC on that beast.

I honestly do not know what my first Linus distro was, whatever was on the machines in the CS half of the computer lab in college. First one I installed myself was Ubuntu, but I abandoned it almost immediately in favor of another distro that I also don't remember.

Windows XP, but it was during its ending phase, so I think it really was Vista. My first Linux distro was Kali Linux because I wanted to be a cool hacker when I was a kid. I never got too much into it then, though. I then found Ubuntu, and strangely enough, I switched to Trisquel, which wasn't too bad. I decided to go all the way and buy a T400 with Libreboot/Trisquel when I was about 15 years old and used that as my second computer for about two years. I learned how to start installing Libreboot myself. It was a really fun experience (not really, there was a lot of quitting and crying), but it taught me more about GNU and the entire philosophy. I started to learn more about GNU and RMS when I was 18. Now I'm 20 and use Arch. The end.

Probably some version of DOS, I can't remember. First Linux distro was Fedora Core 4.

First OS: TRSDOS 1.3

First Linux distro: Slackware 4

For Linux I started with Wubi to install Ubuntu 8.04 Hardy Heron. It installed Linux as a program in Windows and added some kind of hacky boot entry to boot into Ubuntu from your windows partition. Pretty cool, and I'm still pretty nostalgic for the GNOME 2 aesthetic with compiz effects from that time.

First OS was DOS (I think) on an Apple IIE at school. I think there were a few Commodore 64’s there as well. A couple years later we got our first home computer running Windows 95. Good times playing Doom, Jane’s Apache, an MS Flight Simulator.

My first personal computer was running Windows XP and I switched to Ubuntu sometime in 2004. Ran Ubuntu for the most part till a few months ago when I switched my desktop and laptop to NixOS.

Started self hosting services in 2012 and started with Ubuntu as base OS. Now though most of my servers are Proxmox with the VMs usually running Ubuntu LTS, though NixOS is starting to creep in there as well.

MS DOS 2.11.

First OS on a computer I personally owned? Windows 98. First Linux distro was Source Mage.

If not counting ownership, then Apple IIs at school and then slightly later my family got an Amstrad that was primarily a DOS machine, but could also boot (by switching floppies several times) to some sort of GUI.

DOS - Win3.1 - Win95/98 - BeOS - Red Hat Linux - WinXP - Mac OS X - WinVista/7/8 - MacOS X - Win10 - Debian Linux (and staying with it).

My first Linux distro was Ubuntu 5.04 that I got from a free magazine cd from my university.

First social media post that's ever made me feel young! Earliest I remember was Windows 95, but I didn't do much besides play with MS Paint.

On the Linux side: Crunchbang Linux when it was running Debian

I tried Microsoft Windows & Apple OS X before that, but that is is now behind me… as is Debian & Arch being a NixOS user for the last few years.

The first OS I recall using is Windows 7 (yes I’m young), and for Linux, I switched from Windows 11 to Linux Mint, which is what I use in the present day.

Of course Ubuntu was my first Linux distribution. I didn't use it for long.

C64 Basic, Yggdrasil Linux. I wanted to install Minix, in the pre-Linux times, but it was beyond my abilities

First OSish was what came default with the Commodore 64. My first full fledged OS was Windows 3.11. My first Linux distro was Mandrake I think 6.