AMD EPYC 9255 vs AMD Ryzen 9 PRO 9955 Comparison

The AMD EPYC 9255 and the AMD Ryzen 9 PRO 9955 represent two distinct interpretations of the Zen 5 architecture, separated by market segment and physical scale. The EPYC 9255 is a 24-core server processor built for the SP5 socket, while the Ryzen 9 PRO 9955 is a 12-core workstation chip on the AM5 platform. Benchmark data from the head-to-head comparison shows a decisive split: the EPYC 9255 wins 9 of 11 tests, while the Ryzen 9 PRO 9955 takes the remaining 2. The average benchmark score for the EPYC 9255 is 116,388, placing it in the 97th percentile, with its nearest rival, the Intel Xeon 658X, at a delta of 0.3%. The Ryzen 9 PRO 9955 averages 110,612, also in the 97th percentile, trailing the Intel Xeon w7-2595X by 1.8%. This is a story of multi-threaded dominance versus single-thread efficiency.

Where Each One Wins

The AMD EPYC 9255 is the clear winner in almost every throughput-oriented workload. Its largest advantage appears in the PassMark physics test, where it scores 9,740 compared to the Ryzen 9 PRO 9955's 3,332, a delta of 192.3%. This is not an isolated result; the EPYC 9255 also leads by 68.1% in integer math (306,442 vs 182,312) and by 50.9% in floating-point math (183,367 vs 121,509). These are workloads that scale with core count and memory bandwidth, and the EPYC 9255's 24 cores and twelve-channel memory bus provide a structural advantage.

The Ryzen 9 PRO 9955 wins exclusively in single-threaded performance. Its PassMark single-thread score of 4,597 beats the EPYC 9255's 3,655 by 20.5%. This is a meaningful margin for latency-sensitive tasks that rely on a single core's boost clock, which is 5.40 GHz for the Ryzen versus 4.80 GHz for the EPYC. The data compression test, which is often partially single-threaded, still goes to the EPYC 9255 (1,018,904 vs 684,470, a 48.9% delta), indicating that even in mixed workloads, the EPYC's core count overpowers the Ryzen's per-core speed. The Ryzen 9 PRO 9955 is the choice for applications that are strictly single-threaded, while the EPYC 9255 dominates everything else.

Architecture Differences

Both processors are built on TSMC's 4 nm process and use the Zen 5 architecture, but they diverge significantly in physical configuration. The EPYC 9255, codenamed Turin, uses four chiplets, each with a die size of 70.6 mm², totaling 33,260 million transistors. The Ryzen 9 PRO 9955, codenamed Granite Ridge, uses two of the same 70.6 mm² chiplets, but its transistor count is 16,630 million, roughly half. This explains the core count difference: 24 cores and 48 threads for the EPYC versus 12 cores and 24 threads for the Ryzen.

Cache allocation is also asymmetric. Both have 80 KB of L1 and 1 MB of L2 per core, but the L3 cache differs substantially. The EPYC 9255 has 128 MB of shared L3, while the Ryzen 9 PRO 9955 has 64 MB. This larger cache pool is critical for server workloads that repeatedly access large datasets. Memory support further separates them: the EPYC 9255 uses a twelve-channel DDR5 memory bus with a bandwidth of 576.0 GB/s, whereas the Ryzen 9 PRO 9955 uses a dual-channel bus with 89.6 GB/s. Both support ECC memory, but the EPYC's bandwidth is 6.4 times higher.

The socket and PCIe lane counts also reflect their intended roles. The EPYC 9255 uses AMD Socket SP5 and provides 128 PCIe Gen 5 lanes (CPU only), while the Ryzen 9 PRO 9955 uses AMD Socket AM5 and provides 24 lanes. The Ryzen 9 PRO 9955 includes integrated Radeon Graphics, while the EPYC 9255 has no integrated graphics. Power envelopes differ as well: the EPYC 9255 has a TDP of 200, while the Ryzen 9 PRO 9955 is rated at 120. The EPYC 9255 launched on 2024-10-09 with a launch MSRP of $2495, while the Ryzen 9 PRO 9955 has a later release date of 2026-06-29 and no listed launch MSRP.

Head-to-Head Benchmarks

The head-to-head data is unambiguous in most categories. The EPYC 9255's largest win is in the physics test, where its 9,740 score is 192.3% higher than the Ryzen 9 PRO 9955's 3,332. This is a massive delta, suggesting that the EPYC's additional cores and memory bandwidth are transformative for physics simulations. The encryption test shows a 76.8% advantage for the EPYC (59,668 vs 33,754), indicating strong performance in cryptographic workloads. Random string sorting goes to the EPYC by 79.6% (129,202 vs 71,928), a task that benefits from both core count and cache capacity.

Integer math and floating-point math are both strongly in the EPYC's favor, with deltas of 68.1% and 50.9% respectively. The multithread score shows a 39.6% lead for the EPYC (76,580 vs 54,866), which is consistent with its 2x core count advantage. The extended instructions test, which measures SIMD and vector processing, goes to the EPYC by 36.9% (75,185 vs 54,903). The find prime numbers test, often a proxy for integer throughput, shows a 25.8% lead for the EPYC (580 vs 461).

The only two wins for the Ryzen 9 PRO 9955 are in single-thread tests, with identical scores of 4,597 versus the EPYC's 3,655, a 20.5% delta. This is a significant single-core advantage, driven by the Ryzen's higher boost clock of 5.40 GHz. The data compression test, which is won by the EPYC 9255 with a 48.9% delta (1,018,904 vs 684,470), shows that even a partially single-threaded workload cannot overcome the EPYC's parallel processing advantage. The Ryzen's single-thread score places it in a competitive position against the EPYC, but it does not translate into wins elsewhere.

FAQ

Q: Which processor has more cores and threads?

A: The AMD EPYC 9255 has 24 cores and 48 threads, while the AMD Ryzen 9 PRO 9955 has 12 cores and 24 threads.

Q: What is the single-thread performance difference?

A: The Ryzen 9 PRO 9955 wins the PassMark single-thread test with a score of 4,597, which is 20.5% higher than the EPYC 9255's 3,655.

Q: How does memory bandwidth compare?

A: The EPYC 9255 has a twelve-channel memory bus with 576.0 GB/s bandwidth, while the Ryzen 9 PRO 9955 has a dual-channel bus with 89.6 GB/s.

Q: Which processor has a larger L3 cache?

A: The EPYC 9255 has 128 MB of shared L3 cache, while the Ryzen 9 PRO 9955 has 64 MB.

Q: What is the biggest benchmark delta between the two?

A: The largest delta is in the PassMark physics test, where the EPYC 9255 scores 9,740, which is 192.3% higher than the Ryzen 9 PRO 9955's 3,332.

Q: Do both processors support ECC memory?

A: Yes, both the EPYC 9255 and the Ryzen 9 PRO 9955 have ECC memory support.

The Verdict

The benchmark data is clear: the AMD EPYC 9255 is the superior processor for multi-threaded and server-oriented workloads. It wins 9 of 11 head-to-head tests, with deltas ranging from 25.8% in prime number finding to 192.3% in physics. Its 24 cores, 128 MB of L3 cache, and 576.0 GB/s memory bandwidth make it the right choice for database servers, virtualization hosts, and compute-heavy applications that can leverage parallelism. Its average benchmark score of 116,388 is 5.2% higher than the Ryzen 9 PRO 9955's 110,612, and it sits favorably against rivals like the Intel Xeon w7-3565X, which it leads by 1.6%.

The AMD Ryzen 9 PRO 9955 is the pick for workloads that are strictly single-threaded or lightly threaded. Its 5.40 GHz boost clock and single-thread score of 4,597 are 20.5% ahead of the EPYC 9255, making it suitable for applications that cannot scale beyond a few cores. However, its dual-channel memory bus and 12-core configuration limit its multi-threaded ceiling. The data shows a 39.6% deficit in the multithread test and a 50.9% deficit in floating-point math. For a workstation user prioritizing single-core responsiveness over parallel throughput, the Ryzen 9 PRO 9955 offers a clear advantage. For any workload that scales, the EPYC 9255 is the definitive choice.