A rather exciting unannounced AMD mobile Ryzen processor has just surfaced. 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 confirmed yet, but Cezanne could wield AMD’s latest Zen 3 microarchitecture that has been proven to deliver a considerable IPC (instruction per cycle) improvement in comparison to over Zen 2. The Ryzen 7 5800U has already gave 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

Processor Cores / Threads Base / Boost Clocks (GHz) L3 Cache (MB) TDP (W)
Ryzen 9 5900HX* 8 / 16 3.3 / 4.6 16 ?
Ryzen 9 4900H 8 / 16 3.3 / 4.4 8 45
Ryzen 9 4900HS 8 / 16 3.0 / 4.4 8 35

*Specifications are unconfirmed.

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

However, the “X” suffix is real mystery. We have two theories. It could either refer to an even 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 reportedly include a 3.3 GHz base clock and 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 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 have a more accurate idea of the 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 more or less aligns with what the Ryzen 7 5800U presented over the Ryzen 7 4800U

In the case of the Ryzen 9 5900HX, 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. Taking into consideration the big single-core margin in which the Ryzen 9 5900X put up, it’s impossible that it would lose to the Ryzen 9 4900HS in multi-core performance.

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