AMD Instinct MI300 vs AMD Instinct MI355X Comparison

The Verdict

The data distinguishes these two accelerators primarily by generation and capability tier. The AMD Instinct MI300, released in 2023, serves as a high-bandwidth compute platform with a 5 nm process, 128 GB of HBM3 memory, and 47.87 TFLOPS FP32 throughput. The AMD Instinct MI355X, released in 2025, is a newer, larger, and substantially more powerful part: it uses a 3 nm process, packs 288 GB of HBM3e memory, and delivers 78.64 TFLOPS FP32. The MI355X is the clear performance leader in raw compute and memory capacity, while the MI300 offers a lower power envelope at 600 W versus 1400 W, and a conventional 2x 8-pin power connector layout.

For users prioritizing maximum memory capacity and compute density for large-scale AI or HPC workloads, the MI355X is the data-driven choice. Its 288 GB memory capacity is 2.25 times that of the MI300, and its FP32 throughput is 64.3% higher. For those constrained by power delivery or chassis compatibility, the MI300 presents a more modest footprint: its 600 W TDP and 267 mm length contrast with the MI355X’s 1400 W TDP and OAM module form factor (102 mm length, 165 mm width). The MI300 also supports a standard 2x 8-pin power connector, while the MI355X has no discrete power connectors, indicating it is designed for a backplane or baseboard power delivery system.

Architecture Differences

The two accelerators belong to different CDNA generations. The MI300 is built on CDNA 3.0, using TSMC’s 5 nm process, with 153,000 million transistors on a 1017 mm² die, yielding a transistor density of 150.4 million per mm². The MI355X moves to CDNA 4.0, fabricated on TSMC’s 3 nm node, with 185,000 million transistors spread across a much larger 2380 mm² die, resulting in a lower density of 77.7 million per mm². This density drop suggests the MI355X uses more die area for memory stacks or interconnects, consistent with its larger memory pool.

Core counts scale accordingly. The MI300 has 14,080 shading units, 880 texture mapping units, and no ROPs (0 MPixel/s pixel rate). The MI355X increases to 16,384 shading units and 1,024 TMUs, also with zero ROPs. Texture rate jumps from 1,496.0 GTexel/s on the MI300 to 2,457.6 GTexel/s on the MI355X, a 64.3% improvement matching the FP32 gain. Both parts have identical bus widths at 8192 bit, but the MI355X uses HBM3e memory running at 2000 MHz (8 Gbps effective) versus the MI300’s HBM3 at 1300 MHz (5.2 Gbps effective). This yields 8.19 TB/s bandwidth on the MI355X versus 5.32 TB/s on the MI300, a 54% increase.

Clock behavior also differs. Both have a 1000 MHz base clock, but the MI355X boosts to 2400 MHz versus the MI300’s 1700 MHz. FP16 performance is symmetric with FP32 on both parts: 47.87 TFLOPS on the MI300 and 78.64 TFLOPS on the MI355X, both at 1:1 ratio. The MI355X carries a 1400 W TDP and suggests an 1800 W power supply, while the MI300 is rated at 600 W with a 1000 W suggested PSU. The MI355X is an OAM module (102 mm length, 165 mm width), while the MI300 is a PCIe card format (267 mm length, 111 mm height) with 2x 8-pin connectors. Neither part has display outputs or DirectX/OpenGL/Vulkan API support; both are compute-only accelerators on PCIe 5.0 x16 interfaces.

Head-to-Head Benchmarks

The recorded data contains no direct head-to-head benchmark scores, win counts, or rival comparisons. The database lists zero benchmark entries for both parts, and the percentile versus all GPUs is 50 for each, indicating median placement in the overall distribution. However, the specification sheet provides clear deltas that can be interpreted as performance indicators.

The largest single advantage for the MI355X is memory capacity: 288 GB versus 128 GB, a 160 GB difference or 2.25x. This directly impacts model size and batch processing capability. Memory bandwidth follows, with 8.19 TB/s versus 5.32 TB/s, a 54% lead. Compute throughput shows a 64.3% advantage in FP32 and FP16, with 78.64 TFLOPS versus 47.87 TFLOPS. Texture rate mirrors this at 2,457.6 GTexel/s versus 1,496.0 GTexel/s.

The MI300’s advantages are in power and physical integration. Its 600 W TDP is 57.1% lower than the MI355X’s 1400 W. The suggested power supply of 1000 W versus 1800 W reflects a lower system power requirement. The MI300 uses a standard PCIe slot format with 2x 8-pin connectors, while the MI355X requires an OAM module slot with no onboard power connectors, implying a different server infrastructure. The MI300 also has a higher transistor density (150.4M/mm² versus 77.7M/mm²), indicating more efficient use of silicon area, though this does not translate into higher absolute performance.

Boost clock is a significant differentiator: 2400 MHz on the MI355X versus 1700 MHz on the MI300, a 41.2% higher frequency. This contributes directly to the FP32 gain. Base clocks are identical at 1000 MHz, so the MI355X’s advantage emerges under load. Both parts have the same 8192-bit bus width, so bandwidth scaling comes purely from the faster HBM3e memory.

FAQ

Q: Which accelerator has more memory, and by how much?

A: The MI355X has 288 GB of HBM3e memory, while the MI300 has 128 GB of HBM3. That is a 2.25x capacity advantage for the MI355X.

Q: What is the FP32 compute difference between the two?

A: The MI355X delivers 78.64 TFLOPS FP32, while the MI300 delivers 47.87 TFLOPS. The MI355X is 64.3% higher.

Q: Are both parts identical in memory bus width?

A: Yes, both use an 8192-bit bus. However, the MI355X uses HBM3e at 8 Gbps effective, yielding 8.19 TB/s, versus the MI300’s HBM3 at 5.2 Gbps effective, yielding 5.32 TB/s.

Q: What are the power requirements for each?

A: The MI300 has a 600 W TDP and suggests a 1000 W power supply. The MI355X has a 1400 W TDP and suggests an 1800 W power supply. The MI355X uses an OAM module with no power connectors, while the MI300 uses 2x 8-pin connectors.

Q: Which part has a higher boost clock?

A: The MI355X boosts to 2400 MHz, while the MI300 boosts to 1700 MHz. Base clocks are the same at 1000 MHz.

Q: Do these accelerators support graphics APIs?

A: No. Both list DirectX, OpenGL, and Vulkan as N/A, and neither has display outputs. They are compute-only devices.

Where Each One Wins

The MI355X wins decisively in every performance metric related to compute and memory. Its FP32 and FP16 throughput of 78.64 TFLOPS beats the MI300’s 47.87 TFLOPS by 64.3%. Memory bandwidth of 8.19 TB/s exceeds 5.32 TB/s by 54%. Memory capacity of 288 GB versus 128 GB allows the MI355X to handle larger datasets or models without swapping. Texture rate of 2,457.6 GTexel/s versus 1,496.0 GTexel/s follows the same 64.3% gap. The higher boost clock of 2400 MHz versus 1700 MHz supports sustained compute loads. The MI355X is the choice for maximum throughput per accelerator in dense compute clusters.

The MI300 wins in power efficiency and deployment flexibility. Its 600 W TDP is less than half of the MI355X’s 1400 W, meaning a 1000 W PSU suffices versus 1800 W. The MI300’s standard PCIe card form factor (267 mm length, 111 mm height) with 2x 8-pin power connectors fits into conventional server slots, whereas the MI355X requires an OAM module socket (102 mm length, 165 mm width) with no discrete power connectors, which mandates a specialized baseboard. The MI300’s higher transistor density (150.4M/mm² versus 77.7M/mm²) indicates a more compact logic design, though this does not yield higher performance. For systems with limited power budgets or standard PCIe infrastructure, the MI300 is the practical option.

The MI300 also has an earlier release date (2023-01-03) versus the MI355X (2025-06-11), so the MI300 may be more readily available in existing deployments. Both parts share the same bus interface (PCIe 5.0 x16) and have zero ROPs, so neither is suited for rasterization. The MI355X’s 185,000 million transistors versus 153,000 million on the MI300 reflects a larger silicon investment, but the die size of 2380 mm² versus 1017 mm² means the MI355X uses more than twice the area. The MI355X is the raw performance winner; the MI300 is the lower-power, standard-format alternative.