John Carmack makes the case for future GPUs working without a CPU

Forward-looking: John Carmack, the visionary often credited with revolutionizing the first-person shooter genre, is not one to hold back. Known for his straightforward opinions and bold predictions about the future of PC technology, his latest commentary may be his most audacious yet.

John Carmack envisions a future where GPUs could function independently of host CPUs. The legendary programmer behind PC gaming milestones like Commander Keen, Doom, and Quake believes modern GPUs are becoming so powerful and versatile that they could effectively serve as all-in-one “PCs” from the user’s perspective.

Carmack shared his unconventional “GPUs as PCs” concept on X, nostalgically reflecting on the glory days of GPU chains during the Voodoo era. Back when Voodoo2 graphics cards reigned as the most powerful “3D accelerators,” tech-savvy gamers could link two cards using a simple ribbon cable to significantly boost game performance.

With just a ribbon cable, you could double the pixel rate, Carmack noted. He recalled how friends would host hardware parties, combining their 3D cards to enjoy a faster, smoother gaming experience. “Play Quake 2 at 1,280 x 1,024 120 Hz with 4xAA in 1998. If the cards had vertex transform, you could scale out for motion blur and stereo/VR multi-view rendering,” Carmack added.

GPU chains

The Voodoo2 SLI was great – just run a ribbon cable between two cards, and you doubled the pixel rate. No special professional versions were required, so two friends could open up their PCs and put their cards together for a double speed experience, and you really…

– John Carmack (@ID_AA_Carmack) December 6, 2024

Modern rendering engines in games rely heavily on the render-to-texture process, which isn’t well-suited for multiple daisy-chained GPUs. However, Carmack suggested an alternative: GPUs could be arranged in a “ring” topology and enhanced with explicit transfer operations, enabling both 3D rendering and machine learning frameworks to fully exploit the potential of this novel hardware setup.

The former id Software mastermind believes today’s GPUs could eventually operate entirely without host CPUs, provided they have a “private link.” According to Carmack, resourceful (and exceptionally wealthy) users could construct powerful accelerator chains. In such setups, GPUs would generate their own video signal with diagnostic information and receive direct power input, bypassing the need for a traditional host PC system.

These standalone GPUs could potentially run a “tiny” Linux operating system onboard, enabling full computing independence. Input peripherals like mice and keyboards could be managed through a DisplayPort link, offering functionality even in the absence of a USB port.

Carmack’s vision of “computing” GPUs isn’t entirely new. In fact, developers have previously experimented – successfully, in part – with running the original Doom game’s code directly on a GPU instead of relying on a CPU.

Carmack, who spent his later years at Facebook attempting to turn the metaverse concept into reality, left the company to pursue other ventures. More recently, Carmack predicted a significant breakthrough in artificial general intelligence by 2030, continuing his trend of bold, forward-thinking ideas.

Image credit: Drew Campbell