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Comment by VonGuard | Hacker News Reader

Just for the record, the Atari 2600 also had a chess game with AI. It also had only 1024 bits of RAM, but it had access to all of it because there was no OS or underlying hardware support, like in the Speccy. So while this is definitely amazing, the 2600 version is very close in the "insanely well coded" category, especially because the 2600 had some SERIOUSLY quirky hardware to deal with. For example, on the 2600, you could only draw half the screen's background: the other side had to be a mirror image. Additionally, the columns of pixels that you drew on the screen were enumerated, to the halfway point on the screen as follows:

12345678,87654321,1234

So you were drawing forward, backward, then forward again, and that only got you half the screen!

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Not exactly; this overstates the complexity of the chessboard display.

The order isn't exactly what you wrote, it's bits 4567 / 76543210 / 01234567 for the three playfield registers for the left half of the screen. This can be either repeated or mirrored for the right half. A common trick as 2600 Video Chess did was to simply not use the leftmost (mirrored to rightmost) register, which still gets you 16x2 bits of mirrored playfield in the middle, trading computational cost for a slightly smaller play area.

Now an 8x8 checkered board is not symmetrical for mirroring. 2600 Video Chess actually draws only 7 of the files with the mirrored playfield registers, with the center one of the 7 (the 'e' file) straddling the mirror line. The additional (leftmost) file is actually a sprite object (the "ball"). Pretty clever.

The real trick in 2600 Video Chess is drawing 8 sprites per row on a system whose hardware only has 6. It does this with the "venetian blinds" trick, where each sprite is striped onto alternating scanlines. That way there's only ever 4 actual sprites at a time, which are moved back and forth by a square's-width on alternating lines.

This reply is exactly what I love about HN. I'd like to buy you a drink and talk of vintage hardware :)

I read that chess was originally considered impossible to implement on the 2600, but there were promotional materials showing a guy playing chess on it and a customer complained that it wasn't available, so Atari went ahead and wrote it.

The graphics were horrible but the AI was actually pretty good, so we just used to set up a real board and mirror the moves on that.

It may only have had 128 Bytes of RAM, but it used 4K ROM cartridges, even more than that if the cartridge used bank switching. So Atari 2600 programmes had quite a bit more room to fit inside.

IIRC, early cartridges only had 1 or 2k - the 4k was a limit for a while, but I don't think they all shipped with 4k in the beginning (cost savings). IIRC there was a trick later to allow for 8k cartridges (Pitfall II was 8k, I think, but memory may be failing me).

IIRC, Pitfall II was 2K. 255 different levels in 2K, memorable isn't it ? :)

The 2600 hardware is certainly quite... unique, but that didn't stop the demoscene (I'm surprised at no mention of the demoscene in the comments until this post) from doing some rather impressive things with it; here is a memorable recent example of that:

http://www.pouet.net/prod.php?which=64492

It didn't have to be a mirror image; it could also be an unmirrored copy. See, for example, the first screen of the second row of the map to Adventure:

http://www.vgmaps.com/Atlas/Atari2600/Adventure-Variation2.p...

I learned how to play chess as a kid from that 2600 cartridge!

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