Thin and Light AMD Ryzen 7040U ‘Phoenix’ Gets You Ahead

AMD introduced the Ryzen 7040U series

In May, AMD introduced the Ryzen 7040U series of thin and light notebook CPUs, codenamed ‘Phoenix.’ AMD initially announced four Zen 4-based CPUs for ultra-portable notebooks, with the Ryzen 7 7840U (8C/16T) and Ryzen 5 7640U (6C/12T) leading the way with AMD’s first-generation NPU for on-chip AI and inferencing.

A few months later, AMD introduces two more Ryzen 7040U processors. However, these chips use their smaller, optimized Zen 4c cores. AMD’s smaller Zen 4c core debuted with their EPYC 97×4 ‘Bergamo’ processors for native cloud deployments, but server chips were never their only use. Zen 4c was silently released in the consumer market as part of the Ryzen Z1 (non-extreme) CPU used in ASUS’s ROG Ally handheld (2x Zen 4 + 4x Zen 4c), but now it’s being properly introduced in Ryzen laptop chips.

The first of two new Ryzen 7040U processors with Zen 4c is the Ryzen 5 7545U, which has similar specs to the 7540U. The Ryzen 5 7545U’s unusual implementation of two full-fat Zen 4 cores and four Zen 4c cores is the main difference. Second, the Ryzen 3 7440U, a direct successor to the Ryzen 3 7440U, swaps most of its Zen 4 CPU cores for Zen 4c cores.

At the launch of Bergamo, AMD explained that the ‘c’ in Zen 4c stands for ‘Cloud,’ and it’s interesting that AMD chose to integrate Zen 4c in a low-end consumer segment. Comparing Zen 4 and Zen 4c’s core architectures and use cases is intriguing due to their significant differences.

Understanding the technicalities is crucial given AMD’s strategic decision to bring Zen 4c-based parts to consumers with the Ryzen 7040U series. With the Ryzen 5 7545U and Ryzen 3 7440U with Zen 4c hitting the market, understanding the decision is almost as important as extrapolating the performance and capability benefits.

The Zen 4c core is a smaller, feature-identical implementation of Zen 4. It uses denser libraries that can’t clock as high but make the core smaller and more power efficient.

On TSMC’s 5nm process, a conventional Zen 4 core and L2 cache have an area of 3.84 mm², similar to AMD’s initial Zen 4c EPYC chips. Compacting the same architecture on a 5nm process yields a smaller Zen 4c core, measuring 2.48 mm², or 35% smaller. Zen 4c’s basic goals are the same for servers and mobile: a smaller footprint lets AMD fit more cores into the same package. Alternatively, to fit the same CPU cores on a smaller, cheaper die.

AMD went both ways with EPYC server designs. Due to their higher density/smaller size, the EYPC 97×4 ‘Bergamo’ chips have up to 128 Zen 4c cores, 32 more than the top EPYC 9004 Genona chips. AMD’s “budget” EPYC 8004 ‘Siena’ chips with 64 Zen 4c cores over 4 CCDs were cheaper and lower power.

Enabling this smaller Zen 4 requires switching from high-performance libraries and high clockspeeds to high-density libraries. Despite those plumbing changes, Zen 4 and Zen 4c cores have the same features, core IPC, and L2 cache per core for mobile chips. Every figure and buffer, down to SMT, is present and runs clock-for-clock alike.

However, CPU performance is also about clockspeeds, so Zen 4’s area budget was spent on enabling it to clock over 5GHz. High-performance libraries perform well but are not space-efficient. However, high-performance libraries provide the space and features needed to reach chart-topping clockspeeds.

Zen 4c cores performance-wise are identical to Zen 4, but they have lower core clock frequencies. This, combined with high-density libraries’ lower power consumption, improves energy efficiency.

This brings us back to the Zen 4c-based Ryzen 7040U series. In their Ryzen 7040U series, AMD claims that using smaller Zen 4c cores with the same IPC is more power efficient at low TDPs, improving performance for sub-15W chips. The bottom of AMD’s mobile chip stack has lower performance, so we’re first seeing Zen 4c cores here.

Phoenix 2 vs. Phoenix

AMD’s new mobile chips use Phoenix 2, a monolithic silicon die. This is a budget version of AMD’s Ryzen 7000 mobile chips’ Phoenix die. It’s smaller with fewer functional blocks and uses Zen 4c CPU cores instead of Zen 4.

In fact, AMD has used Phoenix 2 before. It’s the most noticeable. AMD Ryzen 7040U silently launched it over the summer as part of the Ryzen Z1 series. The Ryzen Z1 Extreme uses the Phoenix die, while the weaker Ryzen Z1 was the first chip to use Phoenix 2.

AMD made Phoenix 2, which is impressive. Over the past few generations, the company has had a light mobile footprint for various reasons. They’ve never issued two mobile dies for a single architecture before, always using different bins of the same die (e.g. all Rembrandt for Ryzen Mobile 6000). AMD making a second Phoenix chip with Zen 4c cores is a change from the norm. AMD Ryzen 7040U can reach more laptop buyers with multiple chips instead of selling Phoenix (1) chips at high prices. Whether this means AMD will have a wider market presence is unclear.

According to AMD, Phoenix 2’s die size is 137mm², which is 23% smaller than the original 178 mm² Phoenix die. AMD’s budget mobile chip saves die space by removing CPU cores (8x Zen 4 -> 2x Zen 4 + 4x Zen 4c), GPU CUs (12 -> 4), and the Ryzen AI NPU.

AMD could have used Zen 4c cores to pack more cores into a Phoenix-sized die, but they are starting small with smaller chips.

Ryzen 5 7545U and 7440U chips

The Ryzen 5 7545U, a 2x Zen 4 + 4x Zen 4c chip (essentially a Phoenix 2), will headline these new chips. Zen 4c aside, this is the same configuration as the Ryzen 5 7540U, so it will be replaced by the 7545U.

The Ryzen 5 7545U’s peak turbo frequency of 4.9GHz is unchanged because AMD includes two full-fat Zen 4 cores. Other than that, AMD claims both chips share a 3.2 GHz base frequency, meaning the Ryzen 5 7545U has 3.2 GHz Zen 4 and Zen 4c cores. The Ryzen 5 7545U shares 16 MB of L3 cache and 1 MB of L2 cache per core (6 MB).

The second AMD chip with Zen 4c is the Ryzen 3 7440U, which has one Zen 4 and three Zen 4c cores. This budget AMD mobile stack part has the fewest CPU cores (4 total) and the lowest peak clockspeed (4.7GHz for a single core). Besides CPU cores, the chip has 8 MB of L3 cache shared between the cores, 1 MB of L2 cache per core (4 MB total), and AMD’s RDNA 3-based Radeon 740M with four CUs clocked up to 2.5 GHz.

It’s still confusing to distinguish between the ‘new’ and ‘old’ Ryzen 3 7440U. AMD’s website still lists the original 7440U SKU as a pure Zen 4 part from May. AMD doesn’t distinguish between the original Ryzen 3 7440U and the new one with Zen 4c cores; both are the 7440U. AMD confirmed that the Ryzen 3 7440U was always one Zen 4c-based SKU. Despite AMD’s catalog entry, the official line is that the Zen 4-based Ryzen 3 7440U SKU doesn’t exist and that there has always been one.

Unsaid: Zen 4c CPU Cores and Clockspeeds

AMD has treated this, its first use of silicon-heterogenous CPU cores in consumer processors, lightly. AMD markets and documents Zen 4c as Zen 4 because it has the same IPC. While there’s something to be said for simplifying things for the masses, AMD’s briefing left us with some reservations and concerns about what wasn’t said.

AMD clearly states that none of the Zen 4c chips clock higher than 3.1GHz, 1.3GHz (30%) slower than the fastest Genoa chip (9174F) on its server processors. On their consumer chips, AMD only discloses the max turbo clockspeed for the regular Zen 4 core(s) and the base clockspeed for the entire chip. The fastest 7545U is 3.2GHz.

AMD’s server chips have different clockspeed guarantees than their consumer chips. The company guarantees any server CPU core can reach the same max clockspeed (if not all at once), while we favor cores from the consumer side, allowing the best couple to turbo higher.

All of AMD’s disclosures suggest Zen 4c won’t clock above 3GHz, as expected

This is a major difference from a Phoenix (1) chip with Zen 4 cores. Phoenix can get all 8 cores to 4GHz+ under power and thermal conditions, but Zen 4c’s lower clockspeeds are unbeatable. Zen 4c is much slower than Zen 4.

In practice, things won’t be so different. AMD’s performance graphs from their slides are accurate, and a 6/8 core Zen 4 setup can’t reach those clockspeeds in a 15W device. Phoenix 2 is likely more efficient and scores higher in multithreaded scenarios.

However, AMD is not helping themselves by not disclosing the Zen 4c cores’ maximum clockspeeds. AMD wants to hide the differences, but Zen 4 and Zen 4c are different CPU cores. Zen 4c is AMD’s efficiency core and should be treated as such. Which means its clockspeeds must be disclosed separately from the other cores, like Intel and Qualcomm do today.

Would AMD’s messaging have told you the Ryzen 3 7440U had 1 Zen 4 CPU core? How should consumers be informed?

Zen 4c is unique in offering identical IPC to Zen 4, but AMD is hurting its customers by ignoring the differences. IPC and clockspeeds determine CPU performance, so both must be considered. Since AMD has their own efficiency cores, AnandTech believes they should disclose the CPU cores and clockspeeds in their products. Anything less risks deceiving customers, even if AMD doesn’t mean to.

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