AMD Instinct MI355X vs AMD Instinct MI455X Comparison

The Verdict

The AMD Instinct MI355X and MI455X are both accelerator modules designed for high-performance computing, but the data positions them very differently. The MI355X, built on CDNA 4.0, offers a complete, deployable package with 288 GB of HBM3e memory and 78.64 TFLOPS FP32 compute. The MI455X, on CDNA 5.0, is a substantially larger and more capable part, doubling the FP32 throughput to 157.3 TFLOPS and providing 432 GB of HBM4 memory with a vastly wider memory bus.

The database shows the MI455X is the clear performance leader. Its compute and memory specifications dwarf those of the MI355X, making it the choice for workloads where raw throughput and massive memory capacity are the primary constraints. The MI355X, however, uses a 3 nm process node and has a lower power draw of 1400 W, which suggests it can be deployed in systems with less demanding power and cooling infrastructure. The choice between the two is dictated by workload scale: the MI455X for maximum capability, the MI355X for a more balanced, lower-power footprint within its generation.

Architecture Differences

The two accelerators are separated by a full architecture generation. The MI355X uses CDNA 4.0, while the MI455X uses CDNA 5.0. This generational shift is accompanied by a change in manufacturing process. The MI355X is fabricated on a 3 nm node at TSMC, whereas the MI455X moves to a 2 nm node, also at TSMC. This process refinement contributes to a significant increase in transistor count: the MI355X integrates 185,000 million transistors on a die size of 2380 mm², while the MI455X packs 320,000 million transistors into a 2990 mm² die. The resulting transistor density jumps from 77.7M per mm² on the MI355X to 107.0M per mm² on the MI455X.

The compute architecture sees a doubling of the shading units. The MI355X has 16,384 shading units, while the MI455X has 32,768. Both parts feature 1024 texture mapping units, but texture rate remains identical at 2,457.6 GTexel/s, indicating that texture throughput is not the differentiator. Neither part has any ROPs, with pixel rate recorded as 0 MPixel/s, and neither has display outputs or any supported graphics APIs (DirectX, OpenGL, Vulkan all listed as N/A). These are pure compute accelerators.

Memory architecture is a major point of divergence. The MI355X uses 288 GB of HBM3e on an 8192-bit bus, delivering 8.19 TB/s of bandwidth. The MI455X upgrades to 432 GB of HBM4 on a 24576-bit bus, which is three times wider, resulting in a bandwidth of 23.3 TB/s. This is nearly three times the bandwidth of the MI355X. Memory clock speeds are slightly lower on the MI455X at 1900 MHz (7.6 Gbps effective) compared to the MI355X at 2000 MHz (8 Gbps effective), but the massive bus width more than compensates.

The physical and electrical specifications also differ. The MI355X is an OAM Module with dimensions of 102 mm in length and 165 mm in width. The MI455X is an EAM Module with no listed dimensions. Power requirements scale with capability. The MI355X has a TDP of 1400 W and a suggested PSU of 1800 W. The MI455X has a TDP of 2300 W and a suggested PSU of 2700 W. Neither uses power connectors, and both use a PCIe interface, with the MI355X on PCIe 5.0 x16 and the MI455X on PCIe 6.0 x16. The MI355X was released on 2025-06-11, while the MI455X was released later on 2026-07-22.

Head-to-Head Benchmarks

The database records no direct head-to-head benchmark scores for these two parts. The benchmark arrays are empty, and the wins counters for both items are zero. The nearest rivals lists are also empty. Therefore, the analysis must rely on the measured specifications recorded in the database to project performance relationships.

In raw FP32 compute, the MI455X delivers 157.3 TFLOPS, which is exactly double the 78.64 TFLOPS of the MI355X. This is a direct consequence of the doubled shading unit count, as both parts share the same boost clock of 2400 MHz. The FP16 performance is also exactly double, with the MI455X at 157.3 TFLOPS (1:1) versus the MI355X at 78.64 TFLOPS (1:1). This means that for any compute-bound workload, the MI455X has the potential to finish in roughly half the time, assuming the workload scales perfectly with shader count.

Memory bandwidth is another decisive advantage for the MI455X. The database shows 23.3 TB/s for the MI455X versus 8.19 TB/s for the MI355X. This is a 2.84x increase in bandwidth. For workloads that are memory-bound, such as large language model inference or data processing, this difference can be even more impactful than the compute advantage. The MI455X can feed its larger compute array much faster, reducing the likelihood of stalls.

Texture rate is the one specification where the two parts are identical. Both are recorded at 2,457.6 GTexel/s. This suggests that for texture-heavy operations, the performance difference would be limited. However, given that these are compute accelerators with no graphics APIs, texture rate is likely to be a minor factor in real-world usage.

The MI455X also holds the advantage in memory capacity, with 432 GB versus 288 GB. This is a 50% increase, allowing larger models or datasets to reside in high-speed memory without resorting to slower system memory or storage. The MI455X also uses a newer memory type, HBM4, compared to HBM3e on the MI355X.

The process node advantage for the MI455X is evident in the transistor density. The 2 nm node allows 107.0M transistors per mm², versus 77.7M per mm² on the 3 nm node of the MI355X. This density increase is why the MI455X can pack nearly double the transistors (320,000 million versus 185,000 million) without an unreasonable die size increase.

FAQ

Q: How much faster is the MI455X in FP32 compute compared to the MI355X?

A: The MI455X delivers 157.3 TFLOPS FP32, which is exactly double the 78.64 TFLOPS of the MI355X.

Q: What is the memory bandwidth difference between the two accelerators?

A: The MI455X provides 23.3 TB/s of bandwidth via HBM4, while the MI355X provides 8.19 TB/s via HBM3e. The MI455X has nearly three times the memory bandwidth.

Q: Which accelerator has more memory capacity?

A: The MI455X has 432 GB of HBM4 memory, compared to 288 GB of HBM3e on the MI355X. This is a 50% capacity increase.

Q: Are the texture rates different between the MI355X and MI455X?

A: No, both parts are recorded at 2,457.6 GTexel/s, despite the MI455X having double the shading units.

Q: What are the power consumption requirements for each module?

A: The MI355X has a TDP of 1400 W with a suggested PSU of 1800 W. The MI455X has a TDP of 2300 W with a suggested PSU of 2700 W.

Q: Do either of these accelerators support standard graphics APIs?

A: No, both the MI355X and MI455X list DirectX, OpenGL, and Vulkan as N/A. They are compute-only accelerators with no display outputs.

Where Each One Wins

The MI455X wins in every compute and memory metric where the two parts differ. Its FP32 and FP16 throughput of 157.3 TFLOPS is double that of the MI355X. Its memory bandwidth of 23.3 TB/s is 2.84 times higher, and its 432 GB capacity is 50% larger. The MI455X also benefits from a wider 24576-bit memory bus and a more advanced 2 nm process node with higher transistor density. Workloads that are dominated by large matrix multiplications, such as training or inference on very large models, will see the greatest benefit from the MI455X. The higher power envelope of 2300 W is the cost of this performance, and systems must be designed to handle this draw.

The MI355X wins in the areas of power efficiency and deployment flexibility. Its TDP is 1400 W, which is 900 W lower than the MI455X. Its suggested PSU of 1800 W is also lower by 900 W. This makes the MI355X suitable for systems with less robust power delivery or cooling. Its smaller form factor as an OAM Module, with defined dimensions of 102 mm by 165 mm, may also offer more flexibility in certain chassis designs. The MI355X also uses a different memory type, HBM3e, which may be more readily available or supported in existing infrastructure. For workloads where the memory capacity of 288 GB is sufficient and where power constraints are a primary concern, the MI355X is the more practical choice.

The identical texture rate of 2,457.6 GTexel/s on both parts means that neither has an advantage in this specific metric. The identical boost clock of 2400 MHz also means that clock speed is not a differentiating factor. The MI455X uses PCIe 6.0 x16, a newer interface than the PCIe 5.0 x16 on the MI355X, which could reduce host-device transfer bottlenecks in supported systems. The MI355X has a release date of 2025-06-11, while the MI455X is dated 2026-07-22, indicating the MI455X is a later-generation part. Each accelerator serves a distinct tier of the compute market, with the MI455X aimed at maximum throughput and the MI355X at a lower-power profile.