GPU Comparison

The NVIDIA Quadro P400 and NVIDIA GeForce GT 645M represent two very different generations of NVIDIA mobile and workstation graphics. The P400 is a modern, low-power Pascal-based workstation card, while the GT 645M is an older Kepler-based mobile GPU. The benchmark data shows a clear overall winner, but the nature of their respective wins and losses tells a more nuanced story for specific use cases.

Where Each One Wins

The Quadro P400 wins both head-to-head benchmark comparisons in the data, taking 2 wins to the GT 645M's 0. However, the margin of victory is not uniform across tests, which reveals where each card's strengths truly lie.

In the geekbench_opencl test, the Quadro P400 delivers a decisive victory, scoring 4249 against the GT 645M's 2680. This is a 58.5% advantage, indicating that the P400 is substantially better suited for OpenCL compute workloads. This is the clear "workstation" win, if your task involves general-purpose GPU computing, OpenCL acceleration, or any workload that leverages this API, the P400 is the only rational choice here.

The geekbench_vulkan test tells a tighter story. The P400 wins again with a score of 5119 versus 4875, but the delta is just 5%. This is a much closer contest. While the P400 still takes the win, the GT 645M is competitive in Vulkan, meaning for graphics-oriented tasks that use this modern API, the performance gap is nearly negligible. For a user who primarily cares about Vulkan-based rendering or gaming, the GT 645M is not far behind.

The GT 645M does have one benchmark result in its favor that the P400 lacks entirely: a geekbench_metal score of 5679. This is a significant result, as it is the single highest benchmark score recorded for either card. If your application uses Apple's Metal API, the GT 645M has a proven capability that the P400 cannot match, simply because no Metal score exists for the P400 in the data.

Overall, the P400 wins on raw average score (4684 vs 4411), but the GT 645M's strong Metal showing and Vulkan proximity mean it is not without merit in specific software ecosystems.

Architecture Differences

The two cards are built on fundamentally different architectures. The Quadro P400 uses the Pascal architecture with the GP107 chip, fabricated on a 14 nm process at Samsung. In contrast, the GT 645M uses the Kepler architecture with the GK107 chip, built on a 28 nm process at TSMC.

This process difference is stark. The P400 packs 3,300 million transistors into a 132 mm² die, achieving a transistor density of 25.0M / mm². The GT 645M, meanwhile, contains 1,270 million transistors on a 118 mm² die, for a density of just 10.8M / mm². The P400's newer process allows more than twice the transistor density, which is a major factor in its performance-per-watt advantage.

The P400 features 256 shading units, 16 TMUs, and 16 ROPs. The GT 645M has a higher count of shading units at 384, along with 32 TMUs and 16 ROPs. Despite having fewer shading units and TMUs, the P400 achieves superior compute throughput due to its much higher clock speeds (1228 MHz base / 1252 MHz boost vs 709 MHz base / 780 MHz boost).

Memory architecture differs significantly. The P400 uses 2 GB of GDDR5 on a 64-bit bus, delivering 32.06 GB/s of bandwidth. The GT 645M also has 2 GB, but it is DDR3 on a wider 128-bit bus, yielding 28.80 GB/s. The P400's GDDR5 memory runs at an effective 4 Gbps, while the GT 645M's DDR3 runs at just 1800 Mbps effective. This explains why the P400's narrower bus still provides more bandwidth.

The P400 supports DirectX 12 (12_1) and Vulkan 1.4, while the GT 645M is limited to DirectX 12 (11_0) and Vulkan 1.2.175. Both support OpenGL 4.6. The P400 also has no FP16 support listed as a 1:64 ratio, whereas the GT 645M has no FP16 data at all.

Head-to-Head Benchmarks

The most decisive benchmark result is in geekbench_opencl. The P400 scores 4249, which is 58.5% higher than the GT 645M's 2680. This is a massive gap that cannot be explained by clock speed alone; it reflects the architectural efficiency of Pascal over Kepler in compute tasks. The GT 645M's higher shading unit count (384 vs 256) is completely overwhelmed by the P400's higher clocks and superior memory bandwidth per cycle.

In geekbench_vulkan, the difference narrows dramatically. The P400 scores 5119, just 5% ahead of the GT 645M's 4875. This suggests that for Vulkan workloads, the Kepler architecture's higher TMU count (32 vs 16) and wider memory bus (128-bit vs 64-bit) help it remain competitive. The P400's modern feature set and higher clocks edge it out, but this is not a runaway victory.

Looking at the broader benchmark context, the P400's average score of 4684 places it at the 27th percentile of all GPUs. Its nearest rival is the AMD Radeon R8 M445DX, which scores 4727, a -0.9% delta against the P400. The GT 645M's average of 4411 puts it at the 26th percentile, with the Intel Iris Pro Graphics 5200 as a close rival at 4360 (a 1.2% delta favorable to the GT 645M). This means both cards sit in the same performance tier, but the P400 has a slight edge.

The GT 645M's geekbench_metal score of 5679 is noteworthy because it is the highest single score in the entire dataset for either card. In a Metal-specific workload, the GT 645M would likely outperform the P400, though no direct comparison is available.

Specification Differences

The key specification differences between the two cards are numerous and significant:

• Process Node: 14 nm (P400) vs 28 nm (GT 645M)
• Foundry: Samsung vs TSMC
• Transistors: 3,300 million vs 1,270 million
• Die Size: 132 mm² vs 118 mm²
• Base Clock: 1228 MHz vs 709 MHz
• Boost Clock: 1252 MHz vs 780 MHz
• Memory Type: GDDR5 vs DDR3
• Memory Bus: 64 bit vs 128 bit
• Memory Clock: 1002 MHz / 4 Gbps effective vs 900 MHz / 1800 Mbps effective
• Bandwidth: 32.06 GB/s vs 28.80 GB/s
• Shading Units: 256 vs 384
• TMUs: 16 vs 32
• Pixel Rate: 20.03 GPixel/s vs 6.240 GPixel/s
• Texture Rate: 20.03 GTexel/s vs 24.96 GTexel/s
• FP32: 641.0 GFLOPS vs 599.0 GFLOPS
• TDP: 30 W vs 32 W
• DirectX Support: 12 (12_1) vs 12 (11_0)
• Vulkan Support: 1.4 vs 1.2.175
• Slot Width: Single-slot vs IGP
• Display Outputs: 3x mini-DisplayPort 1.4a vs Portable Device Dependent
• Dimensions: 150 mm length, 69 mm height vs no dimensions listed

The P400 also has a suggested PSU of 200 W, while the GT 645M has none listed, reflecting its integrated nature in laptops.

FAQ

Q: Which card has better raw compute performance?

A: The Quadro P400 wins decisively in OpenCL, scoring 4249 versus 2680, a 58.5% advantage.

Q: Is the GT 645M competitive in any modern graphics API?

A: Yes, in Vulkan the GT 645M scores 4875 against the P400's 5119, a difference of just 5%.

Q: Does either card support DirectX 12 Ultimate features?

A: No. The P400 supports DirectX 12 (12_1) and the GT 645M supports DirectX 12 (11_0), neither of which reaches the feature level of DirectX 12 Ultimate.

Q: Which card has higher memory bandwidth?

A: The P400 has 32.06 GB/s of bandwidth despite its 64-bit bus, while the GT 645M has 28.80 GB/s over a 128-bit bus.

Q: Is the GT 645M better for Apple-centric workflows?

A: The data shows the GT 645M has a geekbench_metal score of 5679, the highest single score for either card. No Metal result exists for the P400.

Q: How do these cards compare in overall performance percentile?

A: The P400 sits at the 27th percentile of all GPUs with an average score of 4684, while the GT 645M is at the 26th percentile with an average of 4411.

The Verdict

The data points to a clear choice for most users: the Quadro P400 is the superior card. It wins both head-to-head benchmarks, delivers 58.5% higher OpenCL performance, has twice the transistor density, runs on a modern 14 nm process, and offers significantly higher clocks. Its FP32 output of 641.0 GFLOPS exceeds the GT 645M's 599.0 GFLOPS, and it achieves higher pixel rate (20.03 GPixel/s vs 6.240 GPixel/s) despite having the same ROP count.

The P400 is the pick for anyone running compute workloads, OpenCL-based applications, or any task that benefits from modern architecture features like DirectX 12_1 and Vulkan 1.4. Its single-slot design and 30 W TDP make it a practical choice for workstations, and it has a defined physical footprint at 150 mm in length.

The GT 645M, however, is not without a niche. Its geekbench_metal score of 5679 is the standout number in this entire comparison. If your software stack is built around Apple's Metal API, this card has demonstrated capability that the P400 cannot claim in the data. Its Vulkan performance is also close enough to the P400 that for Vulkan-based rendering, the gap is minor.

For a typical PC builder or workstation user, the Quadro P400 is the obvious recommendation. For a user locked into Metal-specific software on a portable platform, the GT 645M's proven Metal score is the only reason to consider it. Otherwise, the P400's architectural advantages, higher bandwidth, and superior compute results make it the definitive winner in this matchup.