Short answer: Radeon RX 7900 XTX and GeForce RTX 4090 each provide 24GB of dedicated memory, so the same model file has the same nominal file-only margin. RTX 4090 is the safer choice for CUDA-only workflows. RX 7900 XTX can be a viable ROCm route only when the exact operating system, driver, ROCm release, runtime, framework, backend and required operators are supported. Choose from measured results on the intended stack—not cross-architecture core counts or gaming charts.
Official platform comparison
| Official specification | GeForce RTX 4090 | Radeon RX 7900 XTX | Local-AI planning meaning |
|---|---|---|---|
| Architecture | NVIDIA Ada Lovelace | AMD RDNA 3 | Software backends, kernels and supported operators differ |
| Memory | 24GB GDDR6X | 24GB GDDR6 | Same nominal capacity; runtime allocation still depends on the stack |
| Memory interface | 384-bit | 384-bit | Equal width does not establish application throughput |
| Published processing units | 16,384 CUDA cores | 6,144 stream processors / 96 compute units | Architecture-specific counts cannot be normalized directly |
| Reference boost | 2.52GHz | Up to 2.5GHz | Similar clock labels do not make unlike architectures comparable |
| Reference board power | 450W total graphics power | 355W typical board power | Measure complete-system wall power under the same workload |
| Reference system power | 850W | 800W minimum PSU recommendation | Confirm exact board, connectors, cable clearance and system load |
| Reference size | 304 × 137mm; 3-slot | 287mm; 2.5-slot | Partner designs vary; inspect case and airflow clearance |
| NVLink | No | Not an NVIDIA NVLink platform | Multiple cards do not become one automatic 48GB memory pool |
| Primary software gate | CUDA/runtime and driver support | ROCm/backend, OS, driver and framework support | Compatibility must pass before performance or price comparisons |
NVIDIA values describe the RTX 4090 Founders Edition/reference design. AMD values describe the RX 7900 XTX reference design. Add-in-card dimensions, clocks, cooling, power limits and connectors vary.
The same 24GB model-file boundary
These official Qwen2.5-32B-Instruct-GGUF repository display sizes yield the same nominal file-only arithmetic on either 24GB card. They exclude KV cache, runtime workspace, display use, modality, concurrency, allocator behavior and fallback.
| Official artifact | Displayed size | 24GB file-only margin | Planning result on either card |
|---|---|---|---|
| Q2_K | 12.3GB | 11.7GB | Capacity fits; quality and complete allocation require testing |
| Q3_K_M | 15.9GB | 8.1GB | Useful starting point; calculate cache and workspace |
| Q4_K_M | 19.9GB | 4.1GB | Capacity-sensitive; calculate the complete run |
| Q5_K_M | 23.3GB | 0.7GB | Not a safe resident target |
| Q6_K | 26.9GB | Does not fit wholly | Requires another placement, offload or more device memory |
| Q8_0 | 34.8GB | Does not fit wholly | Move to another artifact or capacity tier |
Repository display values checked October 25, 2026. Download size is not peak resident memory.
Software support comes before speed
A CUDA-only application does not become compatible with RX 7900 XTX merely because its memory capacity matches RTX 4090. For AMD, verify the exact current ROCm compatibility matrix, OS, driver, ROCm/runtime version, framework, backend, quantization, kernels and unsupported operators. Windows, WSL and Linux are separate compatibility claims. For NVIDIA, verify the application’s supported CUDA/runtime and driver versions rather than assuming every package supports every Ada configuration.
Compare price, power and board constraints honestly
Compare delivered price for the exact board and condition, not launch price or an unscreened headline listing. Confirm slot width, length, connector routing, cable bend clearance, PSU headroom, cooling, display use, warranty and return protection. If buying used, inspect repair history, fan behavior, memory stability and hotspot-to-core temperature delta with the used-GPU checklist.
Run a controlled cross-backend test
Hold model revision, quantization, context, cache precision, modality, prompt/output profile, batch, concurrency, timing boundary and repetitions constant. Record exact board, OS, driver, backend, CUDA or ROCm/runtime version, kernels, unsupported operators, compilation changes, CPU fallback, offload, exposed memory, peak device memory, system RAM, power limit and wall power. Report failures and fallback instead of hiding them.
Choose the next evidence
Inspect the RX 7900 XTX guide · Inspect the RTX 4090 guide · Compare the 24GB tier · Check CUDA versus ROCm · Calculate complete VRAM · Run a controlled workload · Submit a reproducible result · Stage a private watchlist · Check screened observations
Sources
- NVIDIA GeForce RTX 4090 official specifications
- AMD Radeon RX 7900 XTX official specifications
- AMD ROCm current compatibility matrix
- Official Qwen2.5-32B-Instruct-GGUF repository
- HighVRAM methodology
Reviewed October 25, 2026. HighVRAM has not independently benchmarked these two cards head to head. Specifications, capacity and software support do not establish application speed, output quality or value.