VRAM vs Unified Memory: Mac Apple Silicon vs NVIDIA Compared

Apple Silicon's unified memory architecture eliminates the GPU memory wall entirely. The M4 Max with 128GB uses all of it as "GPU memory" — while an RTX 4090 is capped at 24GB discrete VRAM. This architectural difference fundamentally changes which models you can run.

Architecture Comparison

FeatureNVIDIA Discrete GPUApple Silicon (M4)
Memory typeDedicated VRAMUnified (shared CPU/GPU)
Overflow behaviorCrash or slow swap to RAMGraceful overflow to SSD cache
Max model (consumer)32B at Q4 (RTX 4090)671B MoE models theoretically
Bandwidth (top tier)1,792 GB/s (RTX 5090)800 GB/s (M4 Ultra)

What Models Fit Where

ModelRTX 4090M4 Max 128GBM4 Ultra 192GB
32B Q4Yes (fits)YesYes
70B Q4No (42GB needed)Yes (42GB used)Yes
DeepSeek-R1 671B Q2No (>24GB)Partial (too large)Tight but possible

For a complete comparison of Apple Silicon vs NVIDIA for LLM inference, see LLMHardware.io's full Apple vs NVIDIA comparison.

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