AMD Instinct MI355X vs NVIDIA H800 PCIe 80 GB Comparison

Where Each One Wins

The recorded data shows a clear split between the two accelerators based on workload type. The AMD Instinct MI355X wins decisively in scenarios that demand massive memory capacity, raw FP32 throughput, and extreme memory bandwidth. Its 288 GB of HBM3e memory and 8.19 TB/s bandwidth position it for large-model inference and training datasets that must reside in a single GPU's memory. The MI355X also delivers 78.64 TFLOPS of FP32 compute, which is 53.5% higher than the NVIDIA H800's 51.22 TFLOPS.

The NVIDIA H800 PCIe 80 GB, by contrast, wins in FP16 compute and in any workload that relies on tensor core acceleration. Its 204.9 TFLOPS of FP16 performance (4:1 ratio) is 160.6% higher than the MI355X's 78.64 TFLOPS (1:1 ratio). This makes the H800 the stronger choice for mixed-precision training and inference pipelines where FP16 is the dominant arithmetic format. The H800 also has a higher pixel rate (42.12 GPixel/s versus 0 MPixel/s) and a higher transistor density (98.3M per mm² versus 77.7M per mm²), though the MI355X uses a larger die to reach its transistor count.

The power envelope shifts the balance further. The H800 draws 350 W TDP, while the MI355X draws 1400 W TDP. The H800 also fits in a standard dual-slot PCIe form factor with a 1x 16-pin power connector, whereas the MI355X uses an OAM module with no power connectors and requires a suggested PSU of 1800 W. For dense server racks with power ceilings, the H800 is the more practical option; for a single-slot accelerator with maximum memory and FP32 throughput, the MI355X is the clear winner.

FAQ

Q: Which accelerator has more memory?

A: The AMD Instinct MI355X has 288 GB of HBM3e memory, while the NVIDIA H800 PCIe 80 GB has 80 GB of HBM2e memory. The MI355X also has a wider bus (8192 bit versus 5120 bit) and higher bandwidth (8.19 TB/s versus 2.04 TB/s).

Q: Which one is faster in FP16 compute?

A: The NVIDIA H800 delivers 204.9 TFLOPS of FP16 performance, which is 160.6% higher than the MI355X's 78.64 TFLOPS. The H800 uses a 4:1 FP16 ratio, while the MI355X uses a 1:1 ratio.

Q: What are the power requirements for each?

A: The MI355X has a TDP of 1400 W and a suggested PSU of 1800 W. The H800 has a TDP of 350 W and a suggested PSU of 750 W. The H800 uses a 1x 16-pin power connector, while the MI355X uses no power connectors due to its OAM module form factor.

Q: How do their transistor counts compare?

A: The MI355X contains 185,000 million transistors on a 2380 mm² die, while the H800 contains 80,000 million transistors on an 814 mm² die. The H800 has a higher transistor density (98.3M per mm²) despite using a larger process node (5 nm versus 3 nm).

Q: Which one has more shading units?

A: The MI355X has 16,384 shading units, compared to the H800's 14,592. The MI355X also has more TMUs (1024 versus 456) and a higher texture rate (2,457.6 GTexel/s versus 800.3 GTexel/s).

Q: What is the release timeline for these accelerators?

A: The NVIDIA H800 was released on March 20, 2023, and its production status is Active. The AMD Instinct MI355X was released on June 11, 2025. The H800 lists its predecessor as Server Ada and its successor as Server Blackwell.

Head-to-Head Benchmarks

The head-to-head benchmark dataset contains no recorded entries, so the comparison relies on the specification-level metrics from the database. The most decisive margin is in FP16 compute. The H800's 204.9 TFLOPS versus the MI355X's 78.64 TFLOPS represents a 160.6% advantage for the NVIDIA part. This is a massive gap, and it reflects the H800's tensor core design optimized for FP16 accumulation. The MI355X's FP16 figure matches its FP32 figure exactly (78.64 TFLOPS in both), indicating a 1:1 ratio that does not accelerate half-precision arithmetic.

In FP32, the MI355X reverses the outcome. Its 78.64 TFLOPS is 53.5% higher than the H800's 51.22 TFLOPS. This makes the MI355X the better choice for FP32-heavy workloads such as scientific computing, simulation, and any code that does not use tensor cores. The texture rate also favors the MI355X: 2,457.6 GTexel/s versus 800.3 GTexel/s, a 207.1% difference. The MI355X has 1024 TMUs versus the H800's 456, which explains the texture throughput gap.

Memory bandwidth is another clear win for the MI355X. Its 8.19 TB/s is 301.5% higher than the H800's 2.04 TB/s. Combined with the 288 GB capacity, the MI355X can hold and feed large models without spilling to host memory. The H800's 80 GB and 2.04 TB/s are still respectable for a PCIe card, but they are not in the same class as the MI355X's OAM module.

The H800 does have a higher pixel rate (42.12 GPixel/s versus 0 MPixel/s) and a higher boost clock in terms of base frequency (1095 MHz versus 1000 MHz), though the MI355X has a much higher boost clock (2400 MHz versus 1755 MHz). The H800 also has more ROPs (24 versus 0), which is relevant for any rasterization task, although neither part has display outputs.

Specification Differences

The two accelerators differ across nearly every major specification field. The MI355X uses a 3 nm process from TSMC, while the H800 uses a 5 nm process from the same foundry. The MI355X packs 185,000 million transistors on a 2380 mm² die, versus 80,000 million on 814 mm² for the H800. The transistor density is higher on the H800 (98.3M per mm² versus 77.7M per mm²), which indicates a more compact design, but the MI355X's larger die allows for substantially more compute and memory resources.

Memory configurations are starkly different. The MI355X uses 288 GB of HBM3e with an 8192-bit bus and 8.19 TB/s bandwidth. The H800 uses 80 GB of HBM2e with a 5120-bit bus and 2.04 TB/s bandwidth. The memory clock also differs: the MI355X runs at 2000 MHz (8 Gbps effective), while the H800 runs at 1593 MHz (3.2 Gbps effective).

Compute resources diverge as well. The MI355X has 16,384 shading units, 1024 TMUs, and 0 ROPs. The H800 has 14,592 shading units, 456 TMUs, and 24 ROPs. The MI355X also has no tensor cores listed, while the H800 has 456 tensor cores. The FP32 and FP16 throughput figures follow these resource counts, as described earlier.

The power and form factor differences are significant. The MI355X has a TDP of 1400 W, a suggested PSU of 1800 W, and comes as an OAM module with no power connectors. The H800 has a TDP of 350 W, a suggested PSU of 750 W, uses a 1x 16-pin power connector, and is a dual-slot PCIe card. The dimensions also differ: the MI355X is 102 mm long and 165 mm wide, while the H800 is 268 mm long and 111 mm high.

Architecture Differences

The architectural split is defined by the manufacturing process and the compute design philosophy. The MI355X uses the CDNA 4.0 architecture built on a 3 nm node. Its chip is labeled MI350 256CU, indicating 256 compute units. The H800 uses the Hopper architecture built on a 5 nm node, with the GH100 chip. Both are server-class accelerators with no display outputs, but their design targets are different.

The MI355X's CDNA 4.0 architecture prioritizes raw FP32 throughput and memory capacity. The 1:1 FP16 ratio suggests that the architecture does not specialize in half-precision arithmetic; instead, it focuses on full-precision compute for scientific and HPC workloads. The massive 288 GB memory and 8.19 TB/s bandwidth are designed for large-scale model parallelism where the entire model and its activations must fit in a single accelerator.

The H800's Hopper architecture, by contrast, is built around tensor cores. The 456 tensor cores and 4:1 FP16 ratio deliver 204.9 TFLOPS of half-precision compute, which is 160.6% higher than the MI355X's FP16 figure. This makes the H800 better suited for deep learning training and inference where FP16 is the standard arithmetic format. The H800 also has a higher transistor density (98.3M per mm² versus 77.7M per mm²), which reflects a more area-efficient design despite the older 5 nm node.

The release dates place these architectures in different generations. The H800 launched on March 20, 2023, as part of the Server Hopper generation, with its predecessor listed as Server Ada and successor as Server Blackwell. The MI355X launched on June 11, 2025, as part of the Instinct (MIx) generation, with its predecessor listed as Radeon Instinct. The MI355X is the newer part, and its 3 nm node and larger die reflect that. However, the H800's active production status and lower power envelope (350 W versus 1400 W) give it an ongoing advantage in power-constrained environments.

The memory types also differ: HBM3e on the MI355X versus HBM2e on the H800. The MI355X's memory clock is higher (2000 MHz versus 1593 MHz), and its bus width is wider (8192 bit versus 5120 bit). These architectural choices directly translate into the bandwidth advantage (8.19 TB/s versus 2.04 TB/s) that the MI355X holds. The slot width difference (OAM module versus dual-slot PCIe) further emphasizes the divergent target deployments: the MI355X is meant for high-density accelerator trays, while the H800 is a standard PCIe add-in card.