My first one:

OS: DOS 6.22 (also had Windows 3.11 installed)

486 DX4 100MHZ
8MB Ram (later upgraded to 16MB)
1 3.5" Floppy Drive
500MB Western Digital HDD
1MB SVGA Video Card

It was a good PC for it's time, I spent most of the time in Dos mode playing games like Stonekeep, Screamer 2 and Screamer Rally, Wipeout, Quake 1, Doom and the BUILD engine games, most of them at 320x200 resolution. I've only used Windows for Encarta and school use.

The hard drive failed after 5 years, it started developing bad sectors and nearly anything I tried to run ended up with an error. The last thing I remember playing on it was Quake. The PC ended up completely fried when I was still learning about computers physically and I made the mistake of switching the PSU to from 220v to 130v. The CPU has literally exploded from underneath and popped up from the socket, not a happy ending.

About a year later I got a new Pentium 3 system and that was when I started playing modern games.

The first family computer was a TRS-80 Colour Computer 2. I spent hours picking away at that thing.

Many years later, my first computer that I bought with my own money was a Pentium 100 with 16MB of RAM, 1GB hard drive and a 2MB graphics card running Windows 95. It was awesome! My buddy had a 486DX 100, but mine was better, it was a pentium!

Sinclair ZX Spectrum
CompaQ Portable 3
A 386
And finally a Pentium mmx 166 with 16mb edo-simm, a S3 Trio V64+ card and a 16 bit compatible audio card
Updated to a 233 mmx 128mb, Matrox Millenium 2, 3Dfx Voodoo and Sound Blaster Awe 64 Gold + a Vortex A3D

Got my first PC in early 90's. It was supposed to be a family computer, but I used it almost all the time.
386DX
4MB RAM
40MB HDD
3.5 and 5.25 FDD
B&W monitor (I think 13'')
Can't remember any other specs, but I do remember that case had that infamous lock, so my parents would lock it as a punishment... until the little key misteriously disappeared.

IIRC, you could only use 3.5 kB of the 5 kB of RAM, but you could also buy a RAM expansion separately to increase it to 10 kB. With the C64, you could use an extra 4 kB if you switched off the IO chips, but I don't know if it was possible with a VIC-20... My memory hurts, it's more than 25 years ago! :-p

There were several different RAM upgrades for the VIC-20: 3K, 8K, 16K. From Wikipedia, there were also 32K and 64K third party expansions.

A quick google showed that it was indeed possible to disable the I/O area. I'm not sure how the RAM vs. ROM vs. I/O thing played (don't feel like digging in), but I figure standard usage would have been to use the area for read-only data, by switching I/O off, writing the data, then switching it back on, so writes would do I/O and reads would bring the data stored.

My first computer was one I had as a kid: the Commodore 64. I used it alot for everything (not just games).

I don't recall the first computer I bought myself as an adult.

I just remembered the german nickname for the Commodore 64, it was "Brotkasten" (Breadbox) .

My first computer was an IBM PCjr, which my family bought when I was in 2nd grade (age 7-ish). I'd already used C64s in school a few times, but the IBM was amazing - at the time. :)

I ended up with a typing program, the original King's Quest, and a BASIC cartridge that taught me simple programming before I hit double-digit age. I think we ended up upgrading two or three years later, but we essentially had two computers in the house from that point on: mine, and my grandfather's, and we alternated which one got replaced for years, which meant there were some entertaining arguments over who got to use what at times.

My second computer I honestly don't remember, but I know I ended up with KQIII, KQIV, SQIII, and a CGA/EGA version of Where in the World is Carmen Sandiego? for it.

Oh, we had things like WordStar and dBase, which everyone used, too - but I remember the games. :)

In 1981 I purchased a Sinclar ZX81 kit for $99.99 through mail order from an ad in the Scientific America magazine.

Z80 @ 3.25MHz
1kB RAM, I expanded it to 16kB
used a cassette tape for storage at first, I later hacked in a 180kB floppy drive
I took the board out of the original case and put it in a new larger case which included a standard keyboard, plus I now had room for the other mods I had made for it to be stored inside the new case.

The first PC I bought was a Gateway2000 386SX with 4MB ram and 80MB hard disk, that was in 1991.

I've got my first PC in 2004. What's funny, HDD died the same day I've got it - after I uninstalled some game, Windows just restarted itself and POST stopped at "detecting IDE drives". As for the specs:

AMD Athlon XP 2500+
256MB RAM
80GB HDD
NVIDIA GeForce FX 5200 64MB
OS: Windows XP

My first computer was a Dell Optiplex G1. Not the first computer I used, but man, that machine lasted what I threw against it.

First I had a Commodore 64. Sadly this unit eventually died, but I still have the tape deck and the later-bought 1541C floppy drive that I got for it back then. I have a working unit, but I mostly use modern storage solutions instead of contemporary tapes or disks with it.

Then an Amiga 500 which had my first hard disk, all 50MB of it. I'm not sure what happened to this unit, I thought I gave it to a friend when moving out from a student house, but he doesn't recall this. Perhaps it just got left behind.

After this, an Amiga 1200. This was in 1994, and I used it as my sole computer for several years past it's best-before. Kind of got out of gaming here, because they stopped making games for Amiga. Got more into just being a nerd and tweaking this and that. This one I did give away to a friend when moving, but he has since given it back to me. It still works, and I've upgraded it with hardware both contemporary and modern that I would have drooled over back then.

First PC was a 400MHz AMD with a Voodoo3. I ran Linux, so not many games. But there was Quake 3 at least.

The first? Apple Macintosh Performa 475. 68LC040 at 25MHz, 150 MiB SCSI HDD (later replaced with a 250 MiB one on warranty, because that was the smallest drive they had at the time, several years later replaced with a 4 GiB drive), 4 MiB of RAM (upgraded to 8 MiB at the same warranty issue, then much later to 36 MiB), 512 kiB of VRAM (not yet upgraded, I wouldn't mind an upgrade to 1024 kiB though, to experience some 16-bit graphics goodness as it can only do 256 colours even at 640x480 today), an external 4x SCSI CD-ROM drive, and a 14" Macintosh Color Display. In addition to the mentioned upgrades, it's also received an ethernet card, so it can connect to the net (but not handle much of today's web). Still have the machine in the attic (will be brought back down, some day), but have sadly lost the screen (looking for another one - yes, same model, not just any old Mac screen).

The next machine was a custom built AMD/Windows box. Gigabyte GA-something motherboard, 550MHz AMD Athlon, 128 MiB of RAM, 13 GiB HDD, a DVD-ROM drive (I bought a CD-RW drive a couple years later, when the price had sunk a bit), a 3DFX Voodoo 3 3500 TV AGP, and a 17" Iiyama CRT screen that I sometimes ran at 2048x1536 just because I could (as long as I ran Windows 98, at least, I later switched to Windows 2000 and I guess that OS actually bothered to ask the screen what resolutions and refresh rates it could use), all in an AOpen case. Had a keyboard with Belgian-French layout to use with it, and an awesome ergonomic, tilted, Microsoft mouse that I'm sorry to say I don't think I have any more. Might still have the case somewhere, and I should have the keyboard. The screen is long gone, the Voodoo was borrowed to a friend and hasn't been returned (at the time I was simply happy to have it be used, he was in a much worse financial situation than I was and it was a pretty good upgrade from what he had), and I don't know whether or not I still have the motherboard or CPU.

I used to play a lot on friends' Apple IIs and Vic-20s and the like, but I didn't buy my own until an Atari ST. Loved that thing and still have one in storage.