Memory VRAM and GTT

Memory, VRAM and GTT

All 16 GB on the BC-250 is shared GDDR6 (UMA), so how it's split between the system and the GPU is configurable from the OS.

UMA VRAM (BIOS CMOS)

The fixed slice reserved for the GPU is set in the BIOS CMOS via bc250_memcfg:

• It's persistent (battery-backed) and needs a reboot to take effect.
• The SkillFishOS Tuner exposes it: set the new size, it writes the CMOS and asks you to reboot.
• ⚠️ Don't reserve so much that the system is left short of RAM. It's reversible by clearing the CMOS (jumper on the board).

GTT (shared, dynamic)

Beyond the fixed UMA slice, the GPU can borrow system RAM dynamically through GTT. SkillFishOS lets you grow the GTT budget so the GPU (and the on-device LLM) can use more memory on demand — handy for large models or textures. The Tuner and the AI panel both surface a shared-memory control.

Bandwidth

Memory bandwidth was measured with clpeak/OpenCL at ~350–367 GB/s — healthy and not a bottleneck for gaming. The driver-reported Memory Clock 450 MHz is a reporting convention (not a 1/4 clock), and the memory clock is not adjustable on the BC-250.

See On-device AI for how the GTT split helps local LLMs, and SkillFishOS Tuner for the controls.