AMD Instinct MI455X vs AMD Radeon Instinct MI300 Comparison

# AMD Instinct MI455X vs AMD Radeon Instinct MI300

The AMD Instinct MI455X and the AMD Radeon Instinct MI300 represent two distinct generations of AMD's data center accelerator lineup, with the MI455X built on CDNA 5.0 architecture and the MI300 on CDNA 3.0. The MI455X is a newer, larger, and far more power-hungry design, while the MI300 offers a more established and efficient platform. The recorded data shows a clear split: the MI455X dominates in raw compute throughput and memory capacity, while the MI300 delivers significantly higher FP16 performance per watt and a more practical physical footprint.

Where Each One Wins

The AMD Instinct MI455X wins decisively in scenarios demanding maximum raw compute and memory bandwidth. Its FP32 performance of 157.3 TFLOPS is more than three times the MI300's 47.87 TFLOPS, making it the obvious choice for workloads where single-precision floating-point math is the bottleneck, such as large-scale AI training, scientific simulations, and high-performance computing tasks that rely heavily on dense matrix operations. The MI455X also offers 432 GB of HBM4 memory compared to the MI300's 128 GB of HBM3, and its memory bandwidth of 23.3 TB/s dwarfs the MI300's 6.55 TB/s. For applications that need to hold massive datasets in fast memory or stream data at extreme rates, the MI455X is the clear winner.

The AMD Radeon Instinct MI300 wins in efficiency and practical deployment. Its FP16 performance is 383.0 TFLOPS (8:1), which is substantially higher than the MI455X's FP16 output of 157.3 TFLOPS (1:1). This means that for mixed-precision AI workloads, the older MI300 can actually process more half-precision operations per second than the newer MI455X. When power consumption is factored in, the MI300's 600 W TDP compared to the MI455X's 2300 W TDP gives it a massive advantage in performance per watt for FP16 tasks. The MI300 also uses standard 2x 8-pin power connectors and fits in a 267 mm length, 111 mm height package, while the MI455X requires an EAM Module slot and has no power connectors listed, indicating a custom power delivery system. The MI300 is also built on a more mature 5 nm process from TSMC, whereas the MI455X uses a 2 nm node.

Architecture Differences

The architectural gap between these two accelerators is substantial. The MI455X uses the CDNA 5.0 architecture, while the MI300 is based on CDNA 3.0. This generational leap brings a new process node: the MI455X is fabricated on TSMC's 2 nm process, while the MI300 uses TSMC's 5 nm node. The transistor counts reflect this difference, with the MI455X packing 320,000 million transistors on a 2990 mm² die, compared to the MI300's 153,000 million transistors on a 1017 mm² die. Interestingly, the MI300 has a higher transistor density at 150.4M per mm² versus the MI455X's 107.0M per mm², suggesting the MI455X's larger die uses less dense packing.

The compute resources differ dramatically. The MI455X features 32,768 shading units and 1,024 texture mapping units, while the MI300 has 14,080 shading units and 880 TMUs. Both have 0 ROPs and no RT cores or tensor cores listed, which is typical for compute-focused accelerators. The MI455X's texture rate is 2,457.6 GTexel/s compared to the MI300's 1,496.0 GTexel/s. The clock speeds also differ: the MI455X boosts to 2400 MHz, while the MI300 boosts to 1700 MHz, both with a base clock of 1000 MHz.

Memory architecture represents another major divergence. The MI455X uses HBM4 memory with a 24576-bit bus width, while the MI300 uses HBM3 with an 8192-bit bus. The MI455X's memory clock is 1900 MHz (7.6 Gbps effective), while the MI300's is 1600 MHz (6.4 Gbps effective). The MI455X's 432 GB capacity and 23.3 TB/s bandwidth are far beyond what the MI300 offers. Interface differences also exist: the MI455X uses PCIe 6.0 x16, while the MI300 uses PCIe 5.0 x16. Both have no display outputs.

Head-to-Head Benchmarks

The benchmark data shows a stark contrast in raw computational power. In FP32 performance, the MI455X achieves 157.3 TFLOPS, which is approximately 3.3 times the MI300's 47.87 TFLOPS. This is the largest single-metric advantage for either card. For applications that rely on single-precision math, such as traditional HPC simulations or certain machine learning inference paths, the MI455X provides a massive throughput increase.

In FP16 performance, the situation reverses. The MI300 delivers 383.0 TFLOPS with an 8:1 ratio, while the MI455X delivers 157.3 TFLOPS with a 1:1 ratio. The MI300's FP16 output is approximately 2.4 times higher than the MI455X's. This means that for AI training workloads that use mixed-precision (FP16) arithmetic, the older MI300 can process more data per second than the newer MI455X, despite having fewer shading units and lower memory bandwidth.

The memory bandwidth comparison is also telling. The MI455X's 23.3 TB/s is roughly 3.6 times higher than the MI300's 6.55 TB/s. This bandwidth advantage supports the MI455X's larger memory pool and enables faster data movement for memory-bound workloads. The texture rate follows a similar pattern: the MI455X's 2,457.6 GTexel/s is about 1.6 times the MI300's 1,496.0 GTexel/s.

Power efficiency is where the MI300 wins decisively. With a 600 W TDP versus the MI455X's 2300 W TDP, the MI300 delivers more FP16 performance per watt. The MI300 achieves 383.0 TFLOPS FP16 at 600 W, which is 0.638 TFLOPS per watt. The MI455X achieves 157.3 TFLOPS FP16 at 2300 W, which is 0.068 TFLOPS per watt. The MI300 is roughly 9.4 times more efficient in FP16 per watt. For FP32, the MI300 delivers 47.87 TFLOPS at 600 W (0.080 TFLOPS per watt), while the MI455X delivers 157.3 TFLOPS at 2300 W (0.068 TFLOPS per watt), making the MI300 about 1.2 times more efficient even in FP32.

FAQ

Q: Which card has higher FP32 performance?

A: The AMD Instinct MI455X has significantly higher FP32 performance at 157.3 TFLOPS, compared to the AMD Radeon Instinct MI300's 47.87 TFLOPS. This is more than a three-fold advantage for the MI455X.

Q: Which card has more memory and bandwidth?

A: The MI455X has 432 GB of HBM4 memory with a 24576-bit bus and 23.3 TB/s bandwidth. The MI300 has 128 GB of HBM3 memory with an 8192-bit bus and 6.55 TB/s bandwidth. The MI455X offers roughly 3.4 times more capacity and 3.6 times more bandwidth.

Q: Which card is better for FP16 workloads?

A: The MI300 delivers 383.0 TFLOPS FP16 (8:1), which is higher than the MI455X's 157.3 TFLOPS FP16 (1:1). The MI300 processes about 2.4 times more half-precision operations per second, making it preferable for FP16-heavy AI training.

Q: What are the power consumption differences?

A: The MI455X has a TDP of 2300 W with a suggested PSU of 2700 W, while the MI300 has a TDP of 600 W with a suggested PSU of 1000 W. The MI300 is far more power-efficient, especially for FP16 tasks.

Q: What are the physical and interface differences?

A: The MI455X uses an EAM Module slot with no power connectors listed and no display outputs. The MI300 uses 2x 8-pin power connectors, measures 267 mm by 111 mm, and also has no display outputs. The MI455X uses PCIe 6.0 x16, while the MI300 uses PCIe 5.0 x16.

Q: Which card uses newer manufacturing technology?

A: The MI455X uses TSMC's 2 nm process with 320,000 million transistors on a 2990 mm² die. The MI300 uses TSMC's 5 nm process with 153,000 million transistors on a 1017 mm² die. The MI455X is the newer, more advanced node.

The Verdict

The data indicates that the AMD Instinct MI455X is the choice for workloads that demand absolute maximum compute throughput and memory capacity. Its FP32 performance of 157.3 TFLOPS, 432 GB of HBM4 memory, and 23.3 TB/s bandwidth make it suited for large-scale simulation, scientific computing, and any application where performance is the top priority and power consumption is not a limiting factor. The 2300 W TDP and EAM Module form factor indicate a data center deployment with dedicated cooling and power infrastructure.

The AMD Radeon Instinct MI300 is the choice for FP16-heavy AI workloads and for deployments where power efficiency matters. Its 383.0 TFLOPS FP16 performance exceeds the MI455X's, and its 600 W TDP makes it far easier to integrate into existing systems. The standard 2x 8-pin power connectors and conventional 267 mm length, 111 mm height dimensions mean it can fit into standard server configurations. The MI300's 128 GB memory and 6.55 TB/s bandwidth are lower, but for mixed-precision training where FP16 throughput is the bottleneck, the MI300 delivers more compute per watt and per dollar of infrastructure.

For builders who prioritize raw single-precision throughput and massive memory pools, the MI455X is the clear data-driven selection. For those running FP16 AI training and needing efficient, practical deployment, the MI300's higher FP16 output and dramatically lower power draw make it the more sensible option based on the recorded specifications.

Specification Differences

| Specification | AMD Instinct MI455X | AMD Radeon Instinct MI300 |

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

| Architecture | CDNA 5.0 | CDNA 3.0 |

| Chip | MI450 256CU | Aqua Vanjaram |

| Process Node | 2 nm | 5 nm |

| Transistors | 320,000 million | 153,000 million |

| Die Size | 2990 mm² | 1017 mm² |

| Transistor Density | 107.0M / mm² | 150.4M / mm² |

| Base Clock | 1000 MHz | 1000 MHz |

| Boost Clock | 2400 MHz | 1700 MHz |

| Memory Clock | 1900 MHz (7.6 Gbps effective) | 1600 MHz (6.4 Gbps effective) |

| Memory Size | 432 GB | 128 GB |

| Memory Type | HBM4 | HBM3 |

| Memory Bus Width | 24576 bit | 8192 bit |

| Memory Bandwidth | 23.3 TB/s | 6.55 TB/s |

| Shading Units | 32768 | 14080 |

| TMUs | 1024 | 880 |

| Texture Rate | 2,457.6 GTexel/s | 1,496.0 GTexel/s |

| FP32 Performance | 157.3 TFLOPS | 47.87 TFLOPS |

| FP16 Performance | 157.3 TFLOPS (1:1) | 383.0 TFLOPS (8:1) |

| TDP | 2300 W | 600 W |

| Slot Width | EAM Module | Not specified |

| Power Connectors | None | 2x 8-pin |

| Suggested PSU | 2700 W | 1000 W |

| Bus Interface | PCIe 6.0 x16 | PCIe 5.0 x16 |

| Display Outputs | No outputs | No outputs |

| Dimensions | Not specified | 267 mm, 111 mm |

| Release Date | 2026-07-22 | 2023-01-03 |

| Predecessor | Radeon Instinct | FirePro Data Center |