AMD Radeon HD 6850 X2 vs AMD Radeon R5 M255 Comparison

Head-to-Head Benchmarks

The database contains a single direct comparison between the AMD Radeon R5 M255 and the AMD Radeon HD 6850 X2: the Geekbench OpenCL test. In this benchmark, the R5 M255 records a score of 4650 against the HD 6850 X2's 3977. This places the R5 M255 ahead by 16.9%, a substantial margin in a compute-oriented workload. The result is decisive: the R5 M255 wins the only head-to-head data point available, with a 1 to 0 win count in favor of the newer mobile part.

Looking at how each card sits relative to its own nearest rivals clarifies the context. The R5 M255 has an average benchmark score of 4788, placing it in the 28th percentile of all GPUs in the database. Its closest competitor, the NVIDIA GeForce RTX 3080 12 GB, scores 4791, which is only 0.1% higher. This effectively puts the R5 M255 on par with a desktop flagship from a much later generation in this specific synthetic workload, though the RTX 3080's real-world dominance in gaming is not captured here. The R5 M255 also edges out the AMD Radeon R5 M335 by 0.8% (4752) and the AMD Radeon R8 M445DX by 1.3% (4727), while trailing the NVIDIA GeForce 940MX by 1.2% (4844). These narrow deltas indicate that the R5 M255 sits in a tightly contested cluster of entry-level GPUs, where a few percentage points separate the pack.

The HD 6850 X2, by contrast, has an average benchmark score of 3977, placing it in the 24th percentile. Its nearest rival, the NVIDIA Quadro K2000, scores 3964, a mere 0.3% difference. The HD 6850 X2 also leads the NVIDIA GeForce 830M by 0.5% (3957), the AMD Radeon R5 M420 by 0.5% (3956), and the NVIDIA GeForce GT 745M by 0.6% (3953). The spread among these rivals is even tighter than the R5 M255's group, suggesting that the HD 6850 X2 is firmly anchored in a performance tier where all contenders are nearly indistinguishable in compute benchmarks.

The 16.9% lead in the head-to-head OpenCL test is not trivial. It represents a clear generational efficiency gain: the R5 M255 achieves this result with far fewer resources, as detailed in the next section. The data shows that in raw compute throughput as measured by Geekbench OpenCL, the R5 M255 outperforms the HD 6850 X2, despite the latter having a much larger die and higher power envelope.

Architecture Differences

The two GPUs come from different architectural eras and design philosophies. The AMD Radeon R5 M255 is built on GCN 3.0 architecture, using the Topaz chip, and belongs to the Gem System (R5 M200) generation. It is fabricated on a 28 nm process at TSMC, with 1,550 million transistors on a 125 mm² die, yielding a transistor density of 12.4 million per square millimeter. The HD 6850 X2 uses the older TeraScale 2 architecture, based on the Barts chip, from the Northern Islands (HD 6800) generation. It is built on a 40 nm process, also at TSMC, with 1,700 million transistors on a much larger 255 mm² die, giving a transistor density of only 6.7 million per square millimeter. The process shrink from 40 nm to 28 nm is the primary driver of the R5 M255's higher density and efficiency.

The compute resources differ sharply. The R5 M255 has 384 shading units, 24 texture mapping units, and 8 render output units. The HD 6850 X2 has 960 shading units, 48 TMUs, and 32 ROPs, which is 2.5 times the shader count, double the TMUs, and four times the ROPs. Despite this massive resource advantage, the HD 6850 X2 still loses in the OpenCL benchmark, evidence of the architectural efficiency of GCN 3.0 over TeraScale 2 in compute workloads.

Clock speeds tell a similar story. The R5 M255 has a base clock of 925 MHz and a boost clock of 940 MHz, with memory running at 1000 MHz (2 Gbps effective). The HD 6850 X2 has no listed base or boost clock, but its memory runs at 1050 MHz (4.2 Gbps effective). The R5 M255's higher core clocks, combined with its modern architecture, compensate for its lower raw resource count. The memory subsystems are also very different: the R5 M255 uses 2 GB of DDR3 on a 128-bit bus, yielding 32.00 GB/s of bandwidth. The HD 6850 X2 uses 2 GB of GDDR5 on a 256-bit bus, yielding 134.4 GB/s, over four times the bandwidth.

The feature set diverges as well. The R5 M255 supports DirectX 12 (12_0), OpenGL 4.6, and Vulkan 1.2.170. The HD 6850 X2 is limited to DirectX 11.2 (11_0) and OpenGL 4.4, with no Vulkan support at all. This means the R5 M255 is compatible with modern graphics APIs, while the HD 6850 X2 is locked to older standards. The bus interface also differs: the R5 M255 uses PCIe 3.0 x8, while the HD 6850 X2 uses PCIe 2.0 x16.

Power and physical characteristics are not comparable on equal footing. The R5 M255 has no listed TDP, slot width, power connectors, or suggested PSU. The HD 6850 X2 is a power-hungry dual-slot card with a TDP of 254 W, requiring 2x 8-pin power connectors and a 600 W suggested PSU. It also has display outputs: 2x DVI, 1x HDMI 1.3a, and 1x DisplayPort 1.1. The R5 M255 lists no display outputs in the database, consistent with its likely mobile or small-form-factor target.

FAQ

Q: Which GPU is faster in the Geekbench OpenCL benchmark?

A: The AMD Radeon R5 M255 scores 4650, which is 16.9% higher than the AMD Radeon HD 6850 X2's score of 3977.

Q: How does each GPU compare to its nearest rivals?

A: The R5 M255 has an average score of 4788, nearly matching the NVIDIA GeForce RTX 3080 12 GB (4791, 0.1% lower), and beating the AMD Radeon R5 M335 (4752, 0.8% higher) and AMD Radeon R8 M445DX (4727, 1.3% higher), while trailing the NVIDIA GeForce 940MX (4844, 1.2% lower). The HD 6850 X2 averages 3977, leading the NVIDIA Quadro K2000 (3964, 0.3% higher), NVIDIA GeForce 830M (3957, 0.5% higher), AMD Radeon R5 M420 (3956, 0.5% higher), and NVIDIA GeForce GT 745M (3953, 0.6% higher).

Q: What are the architecture and process node differences?

A: The R5 M255 uses GCN 3.0 architecture on a 28 nm process with 1,550 million transistors on a 125 mm² die. The HD 6850 X2 uses TeraScale 2 on a 40 nm process with 1,700 million transistors on a 255 mm² die.

Q: Which GPU has more shading units and memory bandwidth?

A: The HD 6850 X2 has 960 shading units, 48 TMUs, and 32 ROPs, with 134.4 GB/s of bandwidth from 2 GB of GDDR5 on a 256-bit bus. The R5 M255 has 384 shading units, 24 TMUs, and 8 ROPs, with 32.00 GB/s of bandwidth from 2 GB of DDR3 on a 128-bit bus.

Q: What API support does each GPU offer?

A: The R5 M255 supports DirectX 12 (12_0), OpenGL 4.6, and Vulkan 1.2.170. The HD 6850 X2 supports DirectX 11.2 (11_0) and OpenGL 4.4, with no Vulkan support.

Q: What are the power requirements for the HD 6850 X2?

A: The HD 6850 X2 has a TDP of 254 W, requires 2x 8-pin power connectors, a 600 W suggested PSU, and is a dual-slot card. The R5 M255 has no listed power specifications in the database.

The Verdict

The data points to a clear winner in compute performance: the AMD Radeon R5 M255. Its 16.9% lead in the Geekbench OpenCL benchmark, combined with its higher percentile ranking (28th vs 24th), shows that the newer architecture delivers more performance per unit of silicon. The R5 M255 achieves this with fewer shading units, fewer TMUs, fewer ROPs, and a narrower memory bus, which underscores the efficiency gains of GCN 3.0 over TeraScale 2.

For users prioritizing modern API support, the R5 M255 is the only choice, as it supports DirectX 12, OpenGL 4.6, and Vulkan 1.2.170, while the HD 6850 X2 is limited to DirectX 11.2 and OpenGL 4.4. The R5 M255 also has a boost clock of 940 MHz, which the HD 6850 X2 lacks entirely.

However, the HD 6850 X2 is not without its advantages. It offers 134.4 GB/s of memory bandwidth versus the R5 M255's 32.00 GB/s, a 4.2x difference. It also has 2.5 times the shading units (960 vs 384), double the TMUs (48 vs 24), and four times the ROPs (32 vs 8). For bandwidth-sensitive workloads that do not map well to the OpenCL benchmark, the HD 6850 X2 could potentially be competitive, though the recorded data does not include any such test.

The HD 6850 X2 also requires substantial power delivery: 254 W TDP, 2x 8-pin connectors, and a 600 W suggested PSU. The R5 M255 has no such requirements listed, implying a much lower power draw suitable for mobile or low-power desktop implementations.

The verdict from the database is straightforward: the R5 M255 is the better choice for compute, API compatibility, and efficiency. The HD 6850 X2 retains value only in scenarios where its massive memory bandwidth and raw resource count could be leveraged, but the available benchmark data does not support that case. For most users, the R5 M255 is the superior GPU.

Specification Differences

| Specification | AMD Radeon R5 M255 | AMD Radeon HD 6850 X2 |

| --- | --- | --- |

| Architecture | GCN 3.0 | TeraScale 2 |

| Chip | Topaz | Barts |

| Generation | Gem System (R5 M200) | Northern Islands (HD 6800) |

| Process Node | 28 nm | 40 nm |

| Transistors | 1,550 million | 1,700 million |

| Die Size | 125 mm² | 255 mm² |

| Transistor Density | 12.4M / mm² | 6.7M / mm² |

| Base Clock | 925 MHz | Not listed |

| Boost Clock | 940 MHz | Not listed |

| Memory Clock | 1000 MHz (2 Gbps effective) | 1050 MHz (4.2 Gbps effective) |

| Memory Type | DDR3 | GDDR5 |

| Memory Bus Width | 128 bit | 256 bit |

| Memory Bandwidth | 32.00 GB/s | 134.4 GB/s |

| Shading Units | 384 | 960 |

| TMUs | 24 | 48 |

| ROPs | 8 | 32 |

| Pixel Rate | 7.520 GPixel/s | 25.60 GPixel/s |

| Texture Rate | 22.56 GTexel/s | 38.40 GTexel/s |

| FP32 Performance | 721.9 GFLOPS | 1.536 TFLOPS |

| FP16 Performance | 721.9 GFLOPS (1:1) | Not listed |

| TDP | Not listed | 254 W |

| Slot Width | Not listed | Dual-slot |

| Power Connectors | Not listed | 2x 8-pin |

| Suggested PSU | Not listed | 600 W |

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

| Display Outputs | Not listed | 2x DVI, 1x HDMI 1.3a, 1x DisplayPort 1.1 |

| DirectX Support | 12 (12_0) | 11.2 (11_0) |

| OpenGL Support | 4.6 | 4.4 |

| Vulkan Support | 1.2.170 | Not listed |

| Release Date | 2014-10-11 | 2011-09-18 |

| Predecessor | Solar System | Evergreen |

| Successor | Polaris Mobile | Southern Islands |

| Average Benchmark Score | 4788 | 3977 |

| Percentile vs All GPUs | 28 | 24 |