AMD Radeon HD 6850 X2 vs NVIDIA GeForce GT 645M Comparison

FAQ

Q: Which GPU has the higher average benchmark score?

A: The NVIDIA GeForce GT 645M has an average benchmark score of 4411, while the AMD Radeon HD 6850 X2 scores 3977. The NVIDIA part sits 0.5% above the GeForce 930M (4388) and 1.2% above the Intel Iris Pro Graphics 5200 (4360), whereas the AMD card is only 0.3% ahead of the Quadro K2000 (3964).

Q: How do the two compare in the only shared benchmark test?

A: In Geekbench OpenCL, the AMD Radeon HD 6850 X2 scores 3977 versus the NVIDIA GeForce GT 645M’s 2680. That is a 32.6% margin in AMD’s favor, making it the sole head-to-head win among the available tests.

Q: What is the transistor and die-size relationship between the two chips?

A: The AMD Barts chip packs 1,700 million transistors on a 255 mm² die at 40 nm, yielding a density of 6.7M transistors per mm². The NVIDIA GK107 uses 1,270 million transistors on a 118 mm² die at 28 nm, giving a density of 10.8M per mm². Despite fewer total transistors, the NVIDIA die is less than half the area.

Q: Which GPU has higher memory bandwidth, and why?

A: The AMD Radeon HD 6850 X2 has 134.4 GB/s bandwidth, versus 28.80 GB/s for the NVIDIA GeForce GT 645M. This comes from AMD’s 256-bit bus with GDDR5 at 4.2 Gbps effective, while NVIDIA uses a 128-bit bus with DDR3 at 1800 Mbps effective.

Q: What are the shading unit and texture unit counts?

A: The AMD card has 960 shading units, 48 texture mapping units, and 32 ROPs. The NVIDIA card has 384 shading units, 32 TMUs, and 16 ROPs. AMD’s raw counts are 2.5x higher on shaders and 1.5x higher on TMUs.

Q: Which GPU has a higher pixel fillrate and texture fillrate?

A: The AMD Radeon HD 6850 X2 achieves 25.60 GPixel/s pixel rate and 38.40 GTexel/s texture rate. The NVIDIA GeForce GT 645M reaches 6.240 GPixel/s and 24.96 GTexel/s respectively. AMD leads by a factor of roughly 4x in pixel throughput and 1.5x in texture throughput.

The Verdict

The data separates these two clearly by use case and form factor. The AMD Radeon HD 6850 X2 wins the only direct head-to-head benchmark (Geekbench OpenCL) by 32.6%, and it also dominates in raw throughput metrics: 2.5x the shading units, 1.5x the TMUs, 2x the ROPs, 4.1x the pixel rate, 1.5x the texture rate, and 4.7x the memory bandwidth. If the task is compute-heavy or memory-intensive, the AMD part is the stronger pick.

However, the NVIDIA GeForce GT 645M is a mobile integrated-class part (slot width: IGP, no power connectors, 32 W TDP) versus AMD’s dual-slot desktop card requiring 2x 8-pin connectors and a 600 W suggested PSU. The NVIDIA card also has a higher average benchmark score (4411 vs 3977) and a better percentile rank (26th vs 24th among all GPUs). For systems constrained by power, space, or thermals, the GT 645M is the practical choice despite losing the compute test.

Gamers or compute users with a desktop PSU that can feed 254 W should choose the AMD Radeon HD 6850 X2. Users needing a low-power embedded or laptop solution should pick the NVIDIA GeForce GT 645M. The data does not support a single winner across all metrics; it supports a clear split by hardware context.

Head-to-Head Benchmarks

The only shared benchmark in the data is Geekbench OpenCL. The AMD Radeon HD 6850 X2 scores 3977, while the NVIDIA GeForce GT 645M scores 2680. The delta is 32.6% in AMD’s favor. This is a decisive win, not a marginal one.

To contextualize: the AMD card’s nearest rivals are all within 0.6% of its score (Quadro K2000 at 3964, GeForce 830M at 3957, Radeon R5 M420 at 3956, GeForce GT 745M at 3953). The NVIDIA card’s nearest rivals are also tightly clustered, with the GeForce 930M at 4388 (0.5% higher), Intel Iris Pro 5200 at 4360 (1.2% higher), and RTX 4070 GDDR6 at 4335 (1.8% higher). Notably, the GT 645M’s average score of 4411 is higher than the RTX 4070 GDDR6’s 4335, which is an artifact of the benchmark mix rather than a direct comparison.

The AMD card’s OpenCL score of 3977 is 48.4% higher than the NVIDIA card’s OpenCL score of 2680. That gap is larger than the 32.6% delta reported in the head-to-head table because the table uses the NVIDIA score as the base. Either way, the AMD part is substantially ahead in this specific compute workload.

There are no other head-to-head tests in the data. The NVIDIA card has additional Geekbench Metal (5679) and Geekbench Vulkan (4875) scores that have no AMD counterpart. Those scores contribute to its higher average but cannot be directly compared to the AMD card.

Specification Differences

The two GPUs differ in nearly every measurable specification. The NVIDIA GeForce GT 645M runs at 709 MHz base and 780 MHz boost, while the AMD Radeon HD 6850 X2 has no base or boost clock listed in the data. Memory clocks differ: 900 MHz (1800 Mbps effective) for NVIDIA versus 1050 MHz (4.2 Gbps effective) for AMD.

Memory configuration splits sharply: NVIDIA uses 2 GB DDR3 on a 128-bit bus with 28.80 GB/s bandwidth; AMD uses 2 GB GDDR5 on a 256-bit bus with 134.4 GB/s bandwidth. The bus width is double, and the bandwidth is 4.7x higher on AMD.

Compute resources: NVIDIA has 384 shading units, 32 TMUs, and 16 ROPs. AMD has 960 shading units, 48 TMUs, and 32 ROPs. Pixel rate is 6.240 GPixel/s for NVIDIA versus 25.60 GPixel/s for AMD. Texture rate is 24.96 GTexel/s versus 38.40 GTexel/s. FP32 throughput is 599.0 GFLOPS versus 1.536 TFLOPS, a 2.6x advantage for AMD.

Power and physical specs: NVIDIA is 32 W TDP, IGP slot width, no power connectors, PCIe 3.0 x16. AMD is 254 W TDP, dual-slot, 2x 8-pin power, PCIe 2.0 x16, and a 600 W suggested PSU. Display outputs differ: NVIDIA is “Portable Device Dependent” while AMD has 2x DVI, 1x HDMI 1.3a, and 1x DisplayPort 1.1.

API support: NVIDIA supports DirectX 12 (11_0), OpenGL 4.6, and Vulkan 1.2.175. AMD supports DirectX 11.2 (11_0), OpenGL 4.4, and no Vulkan. Both are end-of-life, but NVIDIA’s API list is more modern.

Architecture Differences

The NVIDIA GeForce GT 645M uses the GK107 chip built on Kepler architecture, manufactured by TSMC at 28 nm. The die is 118 mm² with 1,270 million transistors, giving a density of 10.8M per mm². It belongs to the GeForce 600M generation, preceded by GeForce 500M and succeeded by GeForce 700M.

The AMD Radeon HD 6850 X2 uses the Barts chip on TeraScale 2 architecture, also from TSMC but at 40 nm. The die is 255 mm² with 1,700 million transistors, yielding 6.7M per mm². It is part of the Northern Islands (HD 6800) generation, preceded by Evergreen and succeeded by Southern Islands.

The node difference is significant: 28 nm versus 40 nm explains why NVIDIA achieves higher transistor density (10.8M vs 6.7M per mm²) on a smaller die. The AMD chip uses more total transistors (1,700M vs 1,270M) but spreads them over more than twice the die area.

Architecturally, Kepler is a newer design than TeraScale 2. This shows up in API support: NVIDIA offers Vulkan 1.2.175 and DirectX 12 (11_0), while AMD lacks Vulkan entirely and tops out at DirectX 11.2. The NVIDIA part also has a boost clock mechanism (709 MHz base to 780 MHz boost), while the AMD card lists no boost behavior.

Cache and feature differences are not fully specified in the data. What is clear: the two architectures target different eras and different power envelopes. Kepler is designed for efficiency (32 W TDP), while TeraScale 2 is built for throughput (254 W TDP). The 222 W TDP gap is the largest single architectural consequence.

Where Each One Wins

The AMD Radeon HD 6850 X2 wins in every raw performance metric that appears in the data. It wins the only head-to-head benchmark (Geekbench OpenCL, 3977 vs 2680, +32.6%). It wins in shading units (960 vs 384), TMUs (48 vs 32), ROPs (32 vs 16), pixel rate (25.60 vs 6.240 GPixel/s), texture rate (38.40 vs 24.96 GTexel/s), FP32 (1.536 TFLOPS vs 599.0 GFLOPS), and memory bandwidth (134.4 vs 28.80 GB/s). For compute workloads, rendering pipelines, or any task that scales with shader count or memory throughput, the AMD card is the clear winner.

The NVIDIA GeForce GT 645M wins in efficiency and integration. It has a 32 W TDP versus 254 W, requires no power connectors versus 2x 8-pin, and uses an IGP slot versus dual-slot. It also has a higher average benchmark score (4411 vs 3977) and a higher percentile rank (26th vs 24th). Its Geekbench Metal score of 5679 and Vulkan score of 4875 indicate strong API-specific performance that the AMD card cannot match because it lacks Vulkan support. For compact systems, laptops, or any deployment where power draw and physical footprint matter more than raw compute, the NVIDIA part wins.

The data also shows NVIDIA wins on API modernity: DirectX 12 (11_0), OpenGL 4.6, and Vulkan 1.2.175 versus AMD’s DirectX 11.2, OpenGL 4.4, and no Vulkan. This makes the GT 645M more viable for modern software stacks despite lower raw throughput. The AMD card wins on memory type (GDDR5 vs DDR3) and bus width (256-bit vs 128-bit), which explains its massive bandwidth lead.

In summary: choose AMD for maximum compute and memory throughput in a desktop with adequate power delivery. Choose NVIDIA for low-power, compact, or portable systems and for broader API compatibility. The two GPUs do not compete for the same physical slot; they compete for different users.