Ryzen 9 5900HX: Zen 3 Cezanne May Bring Overclocking to AMD Mobile CPUs

(Image credit: Fritzhez Frenz)

A rather exciting unannounced AMD mobile Ryzen processor has just surfaced recently. The Ryzen 9 5900HX (via Tum_Apisak) could be part of a new breed of Zen 3 mobile chips that may support overclocking, similar to Intel's unlocked HK-series parts.

The Ryzen 9 5900HX, which showed up in an unreleased Asus ROG Zephyrus GX551QS laptop, comes equipped with eight cores, 16 threads, and up to 16MB of L3 cache. Existing Ryzen 4000 (codenamed Renoir) processors have a maximum L3 cache of 8MB, which means that the Ryzen 9 5900HX should belong to the next generation of APUs called Cezanne. Furthermore, the Ryzen 9 5900HX carries the Family 25 Model 80 identifier, the same as Cezanne.

It's not yet confirmed, but Cezanne could wield AMD's latest Zen 3 microarchitecture that has been proven to deliver a considerable IPC (instruction per cycle) improvement compared to  Zen 2. The Ryzen 7 5800U has already given us a sneak peek of what Zen 3 could bring to the table for ultra-thin devices, so it's exciting to see what the microarchitecture can do in a less confined thermal environment.

AMD Ryzen 9 5900HX Specifications

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ProcessorCores / ThreadsBase / Boost Clocks (GHz)L3 Cache (MB)TDP (W)
Ryzen 9 5900HX*8 / 163.3 / 4.616?
Ryzen 9 4900H8 / 163.3 / 4.4845
Ryzen 9 4900HS8 / 163.0 / 4.4835

*Specifications are unconfirmed.

The real eye-opener with the Ryzen 9 5900HX is the "HX" suffix, which AMD hasn't utilized until now. The "H" logically refers to the H-series chips that are AMD's high-performance 45W parts. The chipmaker also has the HS-series, whereby the "S" denotes that it's for slim devices. Basically, HS-series processors are restricted to a 35W TDP and come with slightly lower clock speeds.

However, the "X" suffix is a real mystery that intrigues us. We can think of two plausible theories. The denomination could either refer to a higher clocked version of the H-series with a more generous thermal limit, or perhaps it's AMD's way of saying that the chip has an unlocked multiplier for overclocking.

AMD Ryzen 9 5900HX (Image credit: Primate Labs Inc.)

The Ryzen 9 5900HX's other specifications aren't that impressive. It reportedly has a 3.3 GHz base clock and a 4.59 GHz boost clock. In terms of clock speeds, the Ryzen 9 5900HX appears to feature the same base clock as the Ryzen 9 4900H. However, the unreleased Cezanne part does boast a 200 MHz higher boost clock speed in addition to twice the amount of L3 cache.

According to Geekbench 5, the average single-and multi-core scores for the Ryzen 9 4900HS are 1,092 and 7,072 points. We would need more Ryzen 9 5900HX submissions to get a more accurate picture of the two APUs' performance difference. However, if we only take this single submission as a point of reference, the Ryzen 9 5900HX delivered up to 30.3% higher single-core performance. The margin roughly aligns with what the Ryzen 7 5800U presented over the Ryzen 7 4800U

In this case, the Ryzen 9 4900HS actually came out on top by 2.3% in the multi-core test, suggesting that this might be a bugged run. Considering the big single-core performance gap, it's impossible to think that the Ryzen 9 5900HX would lose to the Ryzen 9 4900HS in a multi-core fight.

Zhiye Liu
RAM Reviewer and News Editor

Zhiye Liu is a Freelance News Writer at Tom’s Hardware US. Although he loves everything that’s hardware, he has a soft spot for CPUs, GPUs, and RAM.

  • spongiemaster
    Great. Another feature to void your warranty straight from the factory.
  • nofanneeded
    Is there PCIe Gen 4 support in it ?
  • Arbie
    Very few actually overclock their desktop PCs, despite all the press that gets. A miniscule number will overclock a laptop where thermals and battery life are so important. And by overclocking Ryzen I think you have to give up its very smart power management - so, a complete waste of time.
  • spentshells
    12 cores to a laptop is promising
  • shady28
    So this has about 8% lower single core than Tiger Lake-U, with a single core freq of 4.6Ghz vs Tiger Lake's 4.7 (2.1% lower freq).

    And its multi-core is about 18% more than Tiger Lake-U despite having 100% more cores?

    And this 35W part is going to compete with upcoming 35W TGL-H how?

  • jkflipflop98
    Overclocking your laptop is dumb. The guys that designed it have very carefully balanced the power draw against the heat against performance. The last thing you need is to let the user go "LOLZ 5GHZ!" and warp their mobo in a week.
  • MasterMadBones
    shady28 said:
    So this has about 8% lower single core than Tiger Lake-U, with a single core freq of 4.6Ghz vs Tiger Lake's 4.7 (2.1% lower freq).

    And its multi-core is about 18% more than Tiger Lake-U despite having 100% more cores?
    Geekbench heavily weights things like ML performance, for which Tiger Lake has dedicated accelerators. Multi-core scores for mobile CPUs are extremely dependent on system configuration, so I'd always encourage people not to read into them too much. In this specific intance, you can point to 4800U entries that have higher MC scores.