GPU Comparison

The NVIDIA GeForce GT 635M and the NVIDIA GeForce 825M are both end-of-life mobile graphics solutions, yet they represent two distinct design philosophies from NVIDIA. The data shows that while they land in the same performance percentile, the architectural gap between them is substantial, leading to different implications for a buyer looking at older laptops.

Head-to-Head Benchmarks

The only direct benchmark comparison available, Geekbench OpenCL, shows a remarkably close contest. The GeForce GT 635M scores 3740, while the GeForce 825M scores 3694. This gives the GT 635M a 1.2% lead in this specific test. In practical terms, this difference is negligible; a 1.2% delta is within run-to-run variance for most OpenCL workloads. The benchmark results indicate that in raw compute throughput, these two GPUs are effectively peers.

However, looking at the nearest rivals for each card reveals how close they are to a cluster of other mobile GPUs. The GT 635M’s rivals include the NVIDIA Quadro 3000M at 3718 (0.6% behind) and the GeForce GT 740M at 3717 (0.6% behind). Meanwhile, the 825M is listed against the same Quadro 3000M and GT 740M, with deltas of -0.6% (meaning it scores lower by that margin). The 825M also sits 1.2% ahead of the AMD Radeon HD 6770. This grouping suggests that the GT 635M and 825M are not just similar to each other but are also interchangeable with a range of contemporary mid-range mobile parts.

Despite the near-identical scores, the way they achieve those scores is fundamentally different. The 825M has a much higher theoretical FP32 throughput of 722.7 GFLOPS, compared to the GT 635M’s 182.4 GFLOPS. This is a massive 3.96x difference in raw compute capability. Yet, the benchmark score shows only a 1.2% difference. This indicates that the OpenCL benchmark is highly sensitive to memory bandwidth, fill rates, or other bottlenecks rather than pure shader compute, as the 825M’s large shader advantage does not translate into a meaningful win here.

Architecture Differences

The two cards are built on entirely different architectures and process nodes. The GT 635M uses the GF108 chip, a Fermi architecture part fabricated on TSMC’s 40 nm process. It packs 585 million transistors into a 116 mm² die. The 825M, on the other hand, uses the GK208 chip with the newer Kepler 2.0 architecture on a 28 nm process. It contains 1,020 million transistors on a smaller 87 mm² die. This is a critical divergence: the 825M has 74% more transistors packed into a 25% smaller physical space, resulting in a transistor density of 11.7M / mm² versus the GT 635M’s 5.0M / mm².

This architectural shift leads to significant differences in core configuration. The GT 635M has 96 shading units, 16 TMUs, and only 4 ROPs. The 825M more than quadruples the shader count to 384, doubles the TMUs to 32, and doubles the ROPs to 8. Consequently, the 825M’s pixel rate is 7.528 GPixel/s and its texture rate is 30.11 GTexel/s, versus the GT 635M’s 1.900 GPixel/s and 7.600 GTexel/s. In any workload that scales well with parallel processing units, the 825M has a structural advantage.

Memory configurations also starkly differ. The GT 635M uses a 128-bit memory bus with 2 GB of DDR3, delivering 28.80 GB/s of bandwidth. The 825M has a narrower 64-bit bus and only 1024 MB of DDR3, halving bandwidth to 14.40 GB/s. This is a major bottleneck for the 825M. Its higher compute power is starved for data, which explains why its OpenCL score does not reflect its superior shader counts. The GT 635M, with double the memory bandwidth, is better suited to feed its smaller number of cores.

Feature-wise, both support DirectX 12 (11_0) and OpenGL 4.6. However, the 825M adds Vulkan 1.2.175 support, while the GT 635M has no Vulkan API listed. The 825M also uses a PCIe 3.0 x8 interface, whereas the GT 635M is limited to PCIe 2.0 x16. Both have a TDP of 35 W (GT 635M) and 33 W (825M), making them suitable for IGP-style integration in laptops, with no power connectors required.

The Verdict

From a strictly data-driven perspective, the GeForce GT 635M wins the only benchmark we have, but the margin is insignificant. The GeForce 825M, however, is the superior part architecturally, offering a 3.96x advantage in FP32 compute, double the texture and pixel rates, and a newer architecture on a more efficient node. Its main weakness is the halved memory bandwidth and smaller frame buffer.

The choice between these two comes down to workload. If you are running applications that are heavily dependent on memory bandwidth and bus width, the GT 635M’s 28.80 GB/s will be more forgiving. If your software is compute-bound and can leverage hundreds of shaders, the 825M’s 722.7 GFLOPS is the clear winner. For gaming at 1080p, the 825M’s low bandwidth and 1 GB VRAM will likely throttle its potential, making the GT 635M’s larger 2 GB buffer and wider bus more practical for texture-heavy titles. For compute tasks like OpenCL acceleration in older productivity apps, the 825M is the better bet. There is no clear overall winner; the data suggests a trade-off between raw compute capability and memory subsystem efficiency.

FAQ

Q: Which GPU has a higher Geekbench OpenCL score?

A: The NVIDIA GeForce GT 635M scores 3740, which is 1.2% higher than the GeForce 825M’s score of 3694.

Q: How does the memory bandwidth compare between the two?

A: The GT 635M has a 128-bit bus with a bandwidth of 28.80 GB/s, while the 825M has a 64-bit bus with a bandwidth of 14.40 GB/s. The GT 635M has exactly double the memory bandwidth.

Q: Which card has more shading units?

A: The GeForce 825M has 384 shading units, compared to the GT 635M’s 96 shading units. This is a four-fold increase.

Q: Do both cards support the same APIs?

A: Both support DirectX 12 (11_0) and OpenGL 4.6. However, the GeForce 825M also supports Vulkan 1.2.175, which is not listed for the GT 635M.

Q: What is the transistor count difference?

A: The GT 635M has 585 million transistors on a 40 nm process, while the 825M has 1,020 million transistors on a 28 nm process.

Q: Which card has a higher pixel fill rate?

A: The GeForce 825M has a pixel rate of 7.528 GPixel/s, which is significantly higher than the GT 635M’s 1.900 GPixel/s.

Where Each One Wins

NVIDIA GeForce GT 635M:

• Memory-Bound Workloads: With a 128-bit bus and 28.80 GB/s bandwidth, it wins in scenarios where data transfer to and from VRAM is the limiting factor. The 2 GB frame buffer also provides more headroom for high-resolution textures.
• OpenCL Benchmarking: It wins the only head-to-head test, the Geekbench OpenCL score, by 1.2%. This suggests it handles mixed compute tasks more efficiently than the 825M, despite the latter’s higher theoretical throughput.
• Legacy Compatibility: It uses the older PCIe 2.0 x16 interface, which is more common in laptops from its 2012 release period.

NVIDIA GeForce 825M:

• Compute-Intensive Tasks: The 722.7 GFLOPS FP32 performance is a massive advantage for any application that can utilize 384 shaders. The GT 635M’s 182.4 GFLOPS is relegated to simpler workloads.
• Texture & Pixel Processing: Doubling the TMUs to 32 and ROPs to 8 yields a texture rate of 30.11 GTexel/s and pixel rate of 7.528 GPixel/s. This makes it faster at filling polygons in 3D rendering.
• Modern Interface & API: The PCIe 3.0 x8 interface and Vulkan 1.2.175 support offer better compatibility with modern software stacks and driver optimizations.
• Efficiency: The 28 nm process allows for more transistors in a smaller die (87 mm²) with a similar TDP (33 W), indicating better power efficiency per unit of compute.

Specification Differences

| Specification | NVIDIA GeForce GT 635M | NVIDIA GeForce 825M |

| :--- | :--- | :--- |

| Architecture | Fermi | Kepler 2.0 |

| Process Node | 40 nm | 28 nm |

| Transistors | 585 million | 1,020 million |

| Die Size | 116 mm² | 87 mm² |

| Transistor Density | 5.0M / mm² | 11.7M / mm² |

| Base Clock | Not specified | 850 MHz |

| Boost Clock | Not specified | 941 MHz |

| Memory Size | 2 GB | 1024 MB |

| Memory Bus Width | 128 bit | 64 bit |

| Memory Bandwidth | 28.80 GB/s | 14.40 GB/s |

| Shading Units | 96 | 384 |

| TMUs | 16 | 32 |

| ROPs | 4 | 8 |

| Pixel Rate | 1.900 GPixel/s | 7.528 GPixel/s |

| Texture Rate | 7.600 GTexel/s | 30.11 GTexel/s |

| FP32 Performance | 182.4 GFLOPS | 722.7 GFLOPS |

| TDP | 35 W | 33 W |

| Bus Interface | PCIe 2.0 x16 | PCIe 3.0 x8 |

| Vulkan API | Not specified | 1.2.175 |