Perhaps the most ridiculous statement that anyone can make is that a computer system with clearly enough processing power ‘cannot run DOOM‘. This is why we accept the premise that a PDP-11 cannot run this game, but something on the order of a Neo Geo gaming console with its 68000 processor and for the time impressive GPU definitely ought to be able to.

The stated problem here is a lack of RAM for a framebuffer, with the CPU only having 64 kB to play with. This limitation now has seen two different approaches to try and circumvent it, as covered by [Modern Vintage Gamer].

The first project here is Doom64kB, which as the name suggests tries to somehow work with this system RAM limitation. It uses the Doom8088 port for the original IBM PC and similar Intel 8088-based systems. This had to massively reduce the feature list, including the lack of texture mapping for floors and ceiling, no saving or loading, and no music.

The other project is DoomGeo, which doesn’t try to bend the Neo Geo hardware to its will, but accepts the Neo Geo way of doing things: involving sprite strips, pre-baked graphics, fix-layer UI, and a minimum of runtime data. This of course drastically changes how the Doom game engine normally works, with its framebuffer-based rendering.

From this we can thus conclude that it’s not so much the processing power that limits where DOOM can run, but more of how framebuffer-friendly the system architecture is, yet with some ingenuity and a complete rewrite of the game engine even that is no major obstacle.

(Top image: Neo Geo AES console. Credit: Evan-Amos, Wikimedia)

Last month, we passed along Modern Vintage Gamer's (MVG) confident assertion that Doom is functionally impossible to run on the Neo Geo, owing to the console's sprite-based display hardware and lack of a frame buffer. We all should have known better than to tell a dedicated group of hackers that something is "impossible," though, as two recent projects have made great progress toward functional Doom ports on stock Neo Geo hardware.

Both of these projects have significant graphical compromises that limit how viable they would have been for a marketable, '90s-era console port, as MVG lays out in a new video. Still, they stand as a testament to the surprising results that clever, determined coders can coax out of legacy hardware.

It looks like Doom if you squint

To create the Doom64KB project for the Neo Geo, coder FrenkelS adapted an earlier Doom port they designed to run on 16-bit PC processors like the 8088 and 286. Using that engine, the Neo Geo code then makes a kind of proto frame buffer out of the console's fix layer, an area of display memory that's usually used to display menus and HUD information on top of gameplay.

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