Upper right quadrant would be an 8-bit (or maybe 16-bit) CPU paired with a 3D graphics capable GPU. SNES + the SuperFX chip is the closest example I can think of. Similarly, there is the Genesis/Mega Drive + SVP chip.
I can't name a fully 8-bit machine with a 3d focused graphics chip. Maybe there are arcade boards?
It's stretching the definition of "3D-focused graphics chip", but an early example might be I, Robot. An 8-bit 6809 CPU drives a custom polygon-pushing graphics processor. It's primitive but must've been mind-blowing in 1984.
Mega Drive is probably earliest that was capable of it really, but Namco System 21 and especially Sega Model 1 (1990) were designed with 3d/polygons in mind but have relatively old chips in them. Programming for those things could not have been easy.
Windows 95 was a big step forward though because it had actual process isolation and preemptive multitasking. While it wasn't very stable compared to Linux or NT, for the most part an application crash wouldn't bring down the whole machine the way it typically happened on classic Mac OS or Windows 3.1.
Larrabee was mostly x86 cores, but it did have sampling/texturing hardware because it's way more efficient to do those particular things in the 3d pipeline with dedicated hardware.
Modern retro computer designs run into the problem of generating a video signal. Ideally you'd have a tile and sprite based rendering. And you'd like to support HDMI or at least VGA. But there are no modern parts that offer this and building the functionality out of discrete components is impractical and unwieldy.
A FPGA is really just the right tool for solving the video problem. Or some projects do it with a micro-controller. But it's sort of too bad as it kind of undercuts the spirit of the whole design. If you video processor is orders of magnitude more powerful than the rest of the computer, then one starts to ask why not just implement the entire computer inside the video processor?
It's one of the funny things of the Raspberry Pi Pico W: The Infineon CYW4343 has an integrated ARM Cortex-M3 CPU, so the WiFi/BT chip is technically more advanced than the actual RP2040 (which is a Cortex-M0+) and also has more built-in ROM/RAM than what's on the Pico board for the RP2040 to use.
And yeah, you can't really buy sprite-based video chips anymore, and you don't even have to worry about stuff like "Sprites per Scanline" because you can get a proper framebuffer for essentially free - but now you might as well go further and use one microprocessor to be the CPU, GPU, and FM Synthesizer Sound Chip and "just" add the logic to generate the actual video/audio signals.
The ability to use a PC as a USB device opens up lots of fun possibilities. It's a little bit tragic that the required xDCI option is there in the hardware on this device, but it's not exposed and requires firmware hacking to access.
The hardware is capable, but the vendor has just turned it off and locked away the controls.
The current and previous generations of xbox and playstation do use x86 CPUs with integrated AMD GPUs. But they aren't just PCs in a small box. Using a unified pool of GDDR memory* is a substantial architectural difference.
*except for the xbox one & one s, which had its own weird setup with unified DDR3 and a programmer controlled ESRAM cache.
In this case he had 150+ of them, so it wouldn't matter too much if he destroyed a few of them in the process. It would be more nerve-wracking to do this on something you don't have many of.
I can't name a fully 8-bit machine with a 3d focused graphics chip. Maybe there are arcade boards?
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