AMD Instinct MI455X vs NVIDIA B300 Comparison

The AMD Instinct MI455X and NVIDIA B300 are two distinct server accelerators aimed at different workloads. The recorded data shows a clear split between raw compute throughput and specialized tensor processing, with each card dominating in separate areas.

Head-to-Head Benchmarks

The database contains no direct benchmark scores for either accelerator, but the recorded technical specifications provide a basis for comparing their theoretical output. In FP32 compute, the AMD Instinct MI455X delivers 157.3 TFLOPS, which is more than double the NVIDIA B300’s 76.99 TFLOPS. That represents a 104% advantage for the AMD part in single-precision floating-point operations, a metric often used for general scientific simulations and traditional HPC workloads.

However, the FP16 comparison flips dramatically. The NVIDIA B300 reaches 1,231.8 TFLOPS with a 16:1 ratio, while the AMD Instinct MI455X manages 157.3 TFLOPS with a 1:1 ratio. The NVIDIA part is approximately 7.8 times faster in half-precision throughput, which directly reflects its tensor core design aimed at AI training and inference.

Memory bandwidth also favors AMD. The Instinct MI455X provides 23.3 TB/s of bandwidth through its HBM4 memory stack, while the B300 offers 4.10 TB/s via HBM3e. The AMD card’s bandwidth is over 4.6 times higher, which matters for data-intensive kernels that saturate memory access. The memory capacity gap is equally wide: 432 GB on the AMD side versus 144 GB on the NVIDIA side, a 3x difference that allows larger datasets to reside on-card.

Texture rate shows AMD ahead at 2,457.6 GTexel/s versus 1,202.9 GTexel/s for NVIDIA. Pixel rate tells a different story, with the B300 producing 48.77 GPixel/s while the MI455X reports 0 MPixel/s, which indicates the AMD card lacks a conventional raster output pipeline.

Clock speeds differ notably. The NVIDIA B300 has a base clock of 1665 MHz and a boost of 2032 MHz, while the AMD Instinct MI455X starts at 1000 MHz base and boosts to 2400 MHz. The AMD card sustains a higher peak frequency but runs at a lower idle base. Memory clocks are 2000 MHz (8 Gbps effective) for NVIDIA and 1900 MHz (7.6 Gbps effective) for AMD, though the AMD’s wider 24576-bit bus compensates with far greater aggregate bandwidth.

Where Each One Wins

The AMD Instinct MI455X wins decisively in scenarios that rely on massive memory capacity and bandwidth. With 432 GB of HBM4 and 23.3 TB/s, it can hold large models or simulation grids entirely on the accelerator, avoiding host-device transfers. The 157.3 TFLOPS FP32 output suits double-precision-heavy scientific computing, climate modeling, and physics simulations where single-precision throughput is the bottleneck. The 2 nm process node and 320,000 million transistors on a 2990 mm² die indicate a design optimized for raw data movement and parallel FP32 execution.

The NVIDIA B300 wins in AI and deep learning contexts. Its 1,231.8 TFLOPS FP16 performance, backed by 592 tensor cores, targets matrix operations for training and inference. The 144 GB HBM3e memory, while smaller, still provides 4.10 TB/s of bandwidth, sufficient for many transformer models. The B300’s 1400 W TDP is lower than the MI455X’s 2300 W, and its SXM Module slot width suggests easier integration into existing NVIDIA server ecosystems. The B300 also has 24 ROPs, allowing some rasterization capability, whereas the MI455X lists zero ROPs.

For texture-bound workloads, the AMD card’s 1024 TMUs and 2,457.6 GTexel/s outperform the B300’s 592 TMUs and 1,202.9 GTexel/s. The MI455X also has more shading units: 32,768 versus 18,944. These point to AMD’s strength in graphics-adjacent compute or non-tensor HPC kernels. The B300 counters with a higher base clock and a more mature production status, listed as Active, while the MI455X has no production status recorded.

Architecture Differences

The two accelerators come from different architectural generations and design philosophies. The AMD Instinct MI455X uses the CDNA 5.0 architecture, built on a 2 nm process at TSMC with 320,000 million transistors. Its die size is 2990 mm², giving a transistor density of 107.0M per mm². The chip is designated MI450 256CU, indicating 256 compute units.

The NVIDIA B300 uses the Blackwell Ultra architecture with the GB110 chip, fabricated on a 5 nm process at TSMC with 104,000 million transistors. No die size or transistor density is recorded for the B300. The process node difference is substantial: 2 nm versus 5 nm, which explains the AMD card’s higher transistor count despite a larger physical footprint.

Memory technology diverges completely. The MI455X uses HBM4 with a 24576-bit bus and 23.3 TB/s bandwidth. The B300 uses HBM3e with a 4096-bit bus and 4.10 TB/s bandwidth. The AMD card’s bus is exactly six times wider, and its memory type is one generation ahead. The capacity delta is 432 GB versus 144 GB, again favoring AMD.

Compute resources differ in kind. The MI455X has 32,768 shading units, 1,024 TMUs, and zero ROPs, with no tensor cores listed. The B300 has 18,944 shading units, 592 TMUs, 24 ROPs, and 592 tensor cores. The FP16 ratio tells the story: AMD uses a 1:1 ratio, meaning FP16 runs at the same rate as FP32, while NVIDIA uses a 16:1 ratio, devoting hardware to packed half-precision ops.

Bus interfaces also vary. The MI455X uses PCIe 6.0 x16, while the B300 uses PCIe 5.0 x16. Power delivery differs: the MI455X has no power connectors (it uses an EAM Module with a 2300 W TDP and a suggested PSU of 2700 W), while the B300 uses an SXM Module with a 1400 W TDP and a suggested PSU of 1800 W. Neither card has display outputs. The AMD part lists no API support for DirectX, OpenGL, or Vulkan; the NVIDIA part leaves those fields null.

Release dates show the B300 launched earlier, on 2025-09-10, with the MI455X following on 2026-07-22. The B300’s predecessor is Server Hopper and successor is Server Rubin; the MI455X’s predecessor is Radeon Instinct, with no successor recorded.

The Verdict

The data indicates two specialized tools. The AMD Instinct MI455X is built for capacity and FP32 throughput. Its 432 GB memory, 23.3 TB/s bandwidth, and 157.3 TFLOPS FP32 output make it suitable for large-scale scientific simulations where datasets exceed 144 GB and where single-precision math dominates. The absence of ROPs and tensor cores confirms it is not designed for rendering or AI matrix multiplication.

The NVIDIA B300 is built for FP16 tensor workloads. Its 1,231.8 TFLOPS FP16 output, 592 tensor cores, and 76.99 TFLOPS FP32 baseline position it for AI training and inference. The 144 GB memory is smaller but still substantial, and the lower 1400 W TDP makes it easier to deploy in power-constrained environments.

The percentile ranking for both cards is 50, with no benchmark scores or nearest rivals recorded, so relative standing against other GPUs cannot be quantified. The choice depends on the workload: the MI455X wins where memory size and FP32 compute matter, while the B300 wins where FP16 tensor performance is the priority. The AMD card’s 2 nm process and PCIe 6.0 interface indicate a newer design, but the B300’s Active production status suggests immediate availability.

FAQ

Q: Which card has higher FP32 performance?

A: The AMD Instinct MI455X delivers 157.3 TFLOPS FP32, which is over twice the NVIDIA B300’s 76.99 TFLOPS.

Q: Which card provides more memory bandwidth?

A: The AMD Instinct MI455X offers 23.3 TB/s from its HBM4 memory, compared to the NVIDIA B300’s 4.10 TB/s from HBM3e.

Q: What is the FP16 performance difference?

A: The NVIDIA B300 reaches 1,231.8 TFLOPS FP16 (16:1 ratio), while the AMD Instinct MI455X delivers 157.3 TFLOPS FP16 (1:1 ratio), making the B300 roughly 7.8 times faster in half-precision.

Q: How do the memory capacities compare?

A: The AMD Instinct MI455X has 432 GB of HBM4, while the NVIDIA B300 has 144 GB of HBM3e, a 3x difference.

Q: What is the power draw for each accelerator?

A: The AMD Instinct MI455X has a TDP of 2300 W with a suggested PSU of 2700 W, while the NVIDIA B300 has a TDP of 1400 W with a suggested PSU of 1800 W.

Q: Which card has tensor cores?

A: Only the NVIDIA B300 lists tensor cores, with 592 units. The AMD Instinct MI455X does not list any tensor cores in the database.