Unified Memory
Apple Silicon's shared CPU/GPU memory. Lets the GPU use system RAM at ~75% available.
On Apple M-series chips, the CPU and GPU share one physical memory pool. By default, macOS reserves about 25% for system processes and lets the GPU use up to 75%. A Mac Studio M4 Ultra 256 GB exposes ~192 GB to the GPU, far more than any consumer NVIDIA card. The catch is bandwidth: 1092 GB/s on M4 Ultra is below A100 (2039) and far below H100 (3350).