Can I Run Phi-4 Mini on 256 GB system RAM?
作者： Jakub Rusinowski · 最后更新： 2025年2月4日
Yes — comfortably
Yes, comfortably — Phi-4 Mini (3.8B) at Q8_0 needs about 5.9 GB of the 204.8 GB usable on 256 GB system RAM, leaving ~198.9 GB spare and running at ~14.2 tok/s (estimated), with room for about 65,536 tokens of context.
Confidence: high · Recommended quantization: Q8_0 · Estimated speed: ~14.2 tok/s
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256 GB system RAM — what it gives a model
| Usable memory for models | 204.8 GB |
| Memory bandwidth | 90 GB/s |
Phi-4 Mini on 256 GB system RAM: memory by quantization
| Quant | Memory needed | Fits 204.8 GB? | Max context | Est. speed | Download |
|---|---|---|---|---|---|
| F16 | 9.5 GB | ✓ Yes | 64K | ~8.1 tok/s | 7.6 GB |
| Q8_0 | 5.9 GB | ✓ Yes | 64K | ~14.2 tok/s | 4 GB |
| Q6_K | 5 GB | ✓ Yes | 64K | ~17.7 tok/s | 3.1 GB |
| Q5_K_M | 4.6 GB | ✓ Yes | 64K | ~19.9 tok/s | 2.7 GB |
| Q4_K_M | 4.2 GB | ✓ Yes | 64K | ~22.5 tok/s | 2.3 GB |
| Q3_K_M | 3.5 GB | ✓ Yes | 64K | ~29.1 tok/s | 1.6 GB |
| Q2_K | 3.1 GB | ✓ Yes | 64K | ~34.7 tok/s | 1.2 GB |
What to watch out for
- These figures assume CPU-only inference. Any discrete GPU, even an 8 GB one, will be several times faster for models that fit in its VRAM.
Recommended setup
llama.cpp (CPU build) or Ollama — both run without a GPU
How these numbers are calculated
- Memory need = quantized weights + KV cache at 8,192 tokens (f16) + 0.8 GB runtime overhead.
- 204.8 GB of the 256 GB is treated as usable for model weights (80% — the rest is the OS and running applications).
- DDR5-5600 dual channel at 89.6 GB/s peak. CPU decode is assumed to sustain 35% of that peak, because CPU inference is not purely bandwidth-bound — it also spends real time in compute and thread synchronisation. This figure is an assumption, not a fitted constant: no CPU measurement is in the calibration set.
- CPU-only inference: no GPU is assumed. A GPU of any size will beat these figures substantially.
- Throughput is a memory-bandwidth roofline estimate, not a measurement. It is labelled "estimated" everywhere it appears.
- KV cache is computed from this model's published attention configuration.
FAQ
Can I run Phi-4 Mini on 256 GB system RAM?
Yes, comfortably — Phi-4 Mini (3.8B) at Q8_0 needs about 5.9 GB of the 204.8 GB usable on 256 GB system RAM, leaving ~198.9 GB spare and running at ~14.2 tok/s (estimated), with room for about 65,536 tokens of context.
Which quantization of Phi-4 Mini should I use on 256 GB system RAM?
Q8_0 — it needs about 5.9 GB of the 204.8 GB available, downloads as roughly 4 GB, and runs at an estimated 14.2 tokens/sec with up to 64K of context.
What limits Phi-4 Mini on 256 GB system RAM?
Nothing binding — the model fits with headroom and generates at a usable speed on this hardware.
Which runtime should I use?
llama.cpp (CPU build) or Ollama — both run without a GPU
Other RAM Capacities
Other Models on 256 GB system RAM
- Poolside Laguna XS 2.1 on 256 GB system RAM
- Qwen 2.5 Family on 256 GB system RAM
- Qwen 2.5 VL on 256 GB system RAM
- Qwen 3 on 256 GB system RAM
- Qwen 3.5 on 256 GB system RAM
Phi-4 Mini on GPUs
- Phi-4 Mini on NVIDIA GeForce RTX 5060 Ti 8GB
- Phi-4 Mini on NVIDIA GeForce RTX 5060
- Phi-4 Mini on NVIDIA GeForce RTX 4060
What This Model Is Good At
Model & Tools
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