AMD EPYC 4585PX vs AMD Ryzen 9 9955HX Comparison

FAQ

Q: Which processor has the higher boost clock?

A: The AMD EPYC 4585PX boosts to 5.70 GHz, while the AMD Ryzen 9 9955HX reaches 5.40 GHz. The EPYC also starts from a higher base clock of 4.30 GHz versus 2.50 GHz for the Ryzen.

Q: How much L3 cache does each chip have?

A: The EPYC 4585PX carries 128 MB of L3 cache, double the 64 MB (shared) found on the Ryzen 9 9955HX. Both use 80 KB of L1 per core and 1 MB of L2 per core.

Q: Do both processors support ECC memory?

A: Yes, both the EPYC 4585PX and the Ryzen 9 9955HX support ECC memory. Both also use DDR5 with a dual-channel memory bus and identical 89.6 GB/s memory bandwidth.

Q: Which chip has more PCIe lanes?

A: The Ryzen 9 9955HX provides 28 CPU-only Gen 5 lanes, while the EPYC 4585PX provides 24 CPU-only Gen 5 lanes.

Q: What is the market segment for each processor?

A: The EPYC 4585PX targets the server/workstation segment, while the Ryzen 9 9955HX is a mobile processor. The EPYC sockets into AMD Socket AM5; the Ryzen uses AMD Socket FL1.

Q: Is one processor unlocked for overclocking?

A: The Ryzen 9 9955HX has an unlocked multiplier; the EPYC 4585PX does not.

Architecture Differences

Both processors are built on the same Zen 5 architecture from AMD, manufactured on a 4 nm process at TSMC. They share identical transistor counts of 16,630 million and the same die size of 2x 70.6 mm². The fundamental building blocks are the same: 16 cores and 32 threads, with 80 KB L1 and 1 MB L2 per core.

The key architectural split appears in the L3 cache and the platform. The EPYC 4585PX carries 128 MB of L3 cache, which is double the 64 MB shared L3 on the Ryzen 9 9955HX. This larger cache pool is typical for a workstation part that needs to hold larger working sets for server-style workloads.

The two chips also differ in their codenames and generations. The EPYC belongs to the EPYC 4005 series with the codename Grado, while the Ryzen 9 9955HX is part of the 9000 series with the codename Fire Range. The release timeline is different as well: the Ryzen launched earlier in 2025, while the EPYC arrived later in May 2025.

Integrated graphics differ notably. The EPYC 4585PX includes Radeon Graphics, while the Ryzen 9 9955HX ships with Radeon 610M. The mobile part also has more PCIe lanes (28 versus 24) and an unlocked multiplier, reflecting its enthusiast mobile positioning. Both support ECC memory, which is unusual for the Ryzen mobile segment.

Head-to-Head Benchmarks

The head-to-head results are one-sided in favor of the EPYC 4585PX, which wins all 15 recorded benchmark comparisons. The most dramatic gaps appear in single-core Cinebench tests. In Cinebench R23 single-core, the EPYC scores 8534 versus 2174 for the Ryzen, a 292.5% advantage. Cinebench R15 single-core shows a 156% lead with scores of 860 versus 336. These are not marginal differences; the EPYC's higher base and boost clocks translate into a massive per-thread advantage.

Multi-core Cinebench results also favor the EPYC heavily. In Cinebench R23 multi-core, the EPYC scores 60451 against 37159, a 62.7% lead. Cinebench R15 multi-core is closer but still decisive: 6093 versus 5905, a 3.2% margin. The EPYC clearly sustains higher throughput across all cores, likely benefiting from its higher power envelope.

PassMark results tell a consistent story, though the margins vary. The largest PassMark gap is in the physics test, where the EPYC scores 6612 versus 2720, a 143.1% lead. Prime number finding shows a 90.6% advantage (547 versus 287). Data encryption comes in at 26.5% ahead (47224 versus 37330), and multithread performance is 22.7% higher (68908 versus 56171).

Other PassMark tests show more moderate but still clear EPYC wins. Floating point math is 12.1% ahead (153219 versus 136682), integer math is 16.9% ahead (248563 versus 212598), extended instructions are 19.9% ahead (69457 versus 57946), data compression is 20.9% ahead (884774 versus 731998), and random string sorting is 22.2% ahead (95210 versus 77890).

The closest result in the entire comparison is PassMark single-thread, where the EPYC scores 4538 versus 4393, a 3.3% edge. This confirms that even in the most favorable test for the Ryzen, the EPYC still wins. The Ryzen 9 9955HX records zero wins across all benchmark comparisons.

Specification Differences

The two processors differ in several key specification fields. Clock speeds are substantially different: the EPYC 4585PX has a 4.30 GHz base clock and 5.70 GHz boost, while the Ryzen 9 9955HX has a 2.50 GHz base and 5.40 GHz boost. This explains the wide single-core benchmark gaps.

Thermal design power is another major differentiator. The EPYC is rated at 170 W TDP, while the Ryzen 9 9955HX is rated at only 55 W. The EPYC draws significantly more power to sustain its higher clocks and performance levels.

Cache configurations differ in L3 only. Both have 80 KB L1 per core and 1 MB L2 per core, but the EPYC has 128 MB L3 versus 64 MB (shared) on the Ryzen. This is a 2x difference in the largest cache level.

Socket and platform differ completely. The EPYC uses AMD Socket AM5, while the Ryzen 9 9955HX uses AMD Socket FL1. This means they are not interchangeable in any system.

PCIe lane counts differ: the EPYC provides 24 Gen 5 lanes (CPU only), while the Ryzen provides 28 Gen 5 lanes (CPU only). The Ryzen has more expansion headroom for its platform.

Integrated graphics differ: the EPYC has Radeon Graphics, while the Ryzen has Radeon 610M. The EPYC's launch MSRP is $699; the Ryzen has no recorded launch MSRP in the database.

The multiplier is locked on the EPYC and unlocked on the Ryzen. This gives the Ryzen overclocking flexibility that the EPYC lacks.

Where Each One Wins

The EPYC 4585PX wins every benchmark category in the recorded data, so the practical question is where the Ryzen 9 9955HX still makes sense. The Ryzen's strengths are contextual rather than benchmark-based. Its 55 W TDP makes it suitable for mobile platforms where power draw and cooling are constrained. The unlocked multiplier appeals to users who want to tune performance manually. Its 28 PCIe lanes provide additional expansion options in a mobile form factor.

For raw compute, the EPYC 4585PX is the clear choice. Its 292.5% lead in Cinebench R23 single-core and 62.7% lead in multi-core indicate it is the stronger processor for both lightly threaded and fully threaded workloads. The PassMark physics test, with a 143.1% advantage, suggests particular strength in simulation or physics-heavy tasks. Data encryption and compression wins of 26.5% and 20.9% respectively point to solid server-side efficiency.

The EPYC also holds a 128 MB L3 cache advantage, which benefits workloads that repeatedly access large datasets. The Ryzen's 64 MB L3 is half that capacity, so the EPYC is better suited for database-style or in-memory processing tasks.

For single-thread responsiveness, the EPYC's 3.3% PassMark single-thread lead and 156% to 292.5% Cinebench single-core leads mean it is also the better choice for per-core performance, despite the Ryzen's higher boost clock potential. The Ryzen's lower base clock of 2.50 GHz appears to constrain its performance in sustained single-thread scenarios.

The Verdict

The data points to a straightforward conclusion. The AMD EPYC 4585PX is the superior processor in every measured benchmark, with wins in all 15 head-to-head comparisons. Its single-core dominance is exceptional: 292.5% ahead in Cinebench R23 single-core and 156% ahead in Cinebench R15 single-core. Multi-core performance is also decisive at 62.7% ahead in Cinebench R23.

The EPYC also holds a 97th percentile ranking among all CPUs, while the Ryzen 9 9955HX sits at the 96th percentile. The EPYC's average benchmark score is 99324, compared to 91199 for the Ryzen. The nearest rivals to the EPYC include the Ryzen Threadripper PRO 9955WX (1.7% higher average score) and the EPYC 7513 (2.9% higher), indicating it sits in strong workstation company. The Ryzen 9 9955HX's nearest rivals include the Intel Core Ultra 7 270K Plus (2.8% higher) and the Intel Xeon 6520P (2.8% higher).

The choice depends on the platform, not the performance. Buyers building a socket AM5 workstation or server should pick the EPYC 4585PX without hesitation. Buyers who need a mobile processor for a laptop or compact system should consider the Ryzen 9 9955HX, accepting its lower performance in exchange for the 55 W TDP and mobile socket. The Ryzen's unlocked multiplier suits enthusiasts who want to overclock, but the recorded benchmark data shows it cannot match the EPYC in any tested workload.

For anyone who can accommodate the 170 W TDP and AM5 socket, the EPYC 4585PX is the clear pick. Its 128 MB L3 cache, higher clocks, and consistent 12% to 292% benchmark leads make it the more capable processor across the board. The Ryzen 9 9955HX is only the right choice when the mobile form factor is a hard requirement.