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Asus ZenFone 2 Review

Asus’ 5.5-inch smartphone comes with an Intel processor and 4GB of RAM. Will its PC-like approach to creating smartphones leave you in a Zen-like state?

CPU And System Performance

In this section, we evaluate system-level performance by running a series of synthetic and real-world workloads, along with some browser-based Web tests. There are several facets to overall device performance, including single- and multi-threaded CPU performance, memory and storage speed, and GPU rendering, all of which will be probed by our suite of benchmarks. If you're interested in learning more about how these benchmarks work, what versions we use, or our testing methodology, please read our article about how we test mobile device system performance.

ProductsCPUGPURAM
Asus ZenFone 2Intel Atom Z3580 (4x @ 2.33GHz)PowerVR G6430 @ 533MHz4GB
Apple iPhone 6 PlusApple Cyclone+ (2x @ 1.4GHz)PowerVR GX64501GB
Motorola Moto G (3rd gen)Snapdragon 410ARM Cortex-A53 (4x @ 1.36GHz)Adreno 306 @ 400MHz2GB
Sony Xperia M4 AquaSnapdragon 615ARM Cortex-A53 (4x @ 1.5GHz + 4x @ 1.0GHz)Adreno 405 @ 550MHz2GB
LG G4Snapdragon 808ARM Cortex-A57 (2x @ 1.82GHz) + ARM Cortex-A53 (4x @ 1.44GHz)Adreno 418 @ 600MHz3GB
Samsung Galaxy S6Exynos 7420ARM Cortex-A57 (4x @ 2.1GHz) + ARM Cortex-A53 (4x @ 1.5GHz)ARM Mali-T760MP8 @ 772MHz3GB

The ZenFone 2 we’re testing comes with an Intel Atom Z3580 SoC and 4GB RAM. The 64-bit, quad-core CPU idles at 500MHz and ramps up to a maximum of 2.33GHz. Because this is the first time we’ve tested the Atom in a phone, we’re going to compare it to several different SoCs (shown in the table above) to determine where it falls in terms of performance.

Looking first at the System test, which evaluates single- and multi-threaded integer and floating-point performance, the ZenFone 2 scores 1.72x better than the Moto G (3rd gen). With the same core count as the Snapdragon 410, the 1.71x difference in CPU clock frequency implies that an Atom core performs about the same as an A53 core clock for clock. The ZenFone 2’s Atom SoC scores 34% lower than the A8 in the iPhone 6 Plus and 43% lower than Samsung’s Exynos 7420, its eight CPU cores adding to its advantage.

The ZenFone 2’s PowerVR G6430 GPU is bracketed by the Adreno 405 and the Adreno 418 in the Graphics test. It’s no surprise to see the iPhone 6 Plus perform better either, since it’s using a newer, more powerful configuration of the PowerVR GPU.

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In the AndEBench Pro suite, the ZenFone 2 scores only 10% lower overall than the LG G4 and 24% lower than the Galaxy S6 (currently the fastest Android phone), giving the ZenFone 2 a superior performance-per-dollar ratio.

Digging a bit deeper shows the Atom SoC in the ZenFone 2 outperforming the Snapdragon 410 in the Moto G (3rd gen) by ~2.5x in the CPU-centric CoreMark-Pro test. This is an even larger margin than we saw in Basemark OS II System, with performance scaling greater than the clock frequency difference. The ZenFone 2 even outperforms the G4 in this test by 15%. This is because the G4 only utilizes its two A57 cores (the A53 cores remain mostly idle) versus the ZenFone 2’s four CPU cores.

The Atom SoC uses LPDDR3 RAM at 800MHz, limiting maximum bandwidth to 12.8 GB/s. It’s no surprise then to see the ZenFone 2 perform similarly to the Moto G (3rd gen) and Xperia M4 Aqua in the Memory Bandwidth test. The LPDDR4-1600MHz RAM in the Galaxy S6 far outpaces it, but so does the LPDDR3-933MHz RAM (14.9 GB/s) in the G4, far more than we’d expect based on theoretical bandwidth alone. We’ve seen similar behavior from the Snapdragon 810, and we believe this is because Qualcomm’s latest memory controllers are optimized for serial access. Further evidence for this hypothesis comes from the Memory Latency test, which uses a random access memory pattern, where the G4 falls to the bottom of the chart. With its stronger performance in the Memory Latency test, the ZenFone 2’s memory subsystem should perform well during normal application use but struggle a bit when reading/writing large blocks of serial data, like photos and videos.

The Platform test, which simulates a real-world workload, shows that the ZenFone 2 does indeed perform quite well in a normal use case. It even outperforms the Galaxy S6!

AndEBench Pro Storage Test
512BSW512BRW4KBSR4KBSW4KBRR4KBRW16KBRR256KBSR256KBRR
ZenFone 223070222417170622899555053749113614104668
Galaxy Note 4449102520877334020425799256653125891127268
ZenFone 2 % Diff-48.8%-31.5%7.4%-48.9%12.1%-30.6%-5.1%-9.8%-17.8%
First letter: S=sequential, R=randomSecond letter: R=read, W=writeValues in KB/s - Higher is betterFile Size: 5, #Folders: 3, #Files/Folder: 1

The ZenFone 2’s internal storage performance is typical for a mid-range phone. Read performance is pretty decent, about on par with the Galaxy Note 4. This is important because read performance impacts the user experience more than write performance; it limits how quickly apps can launch. From these performance numbers, we can see that the ZenFone 2 launches apps nearly as quickly as the more expensive Note 4.

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Looking at the Geekbench single-core results confirms what we saw in the Basemark OS II System test. Namely, a Silvermont CPU core is roughly equivalent to an A53 core at the same clock frequency. The ZenFone 2, which has a 1.71x advantage in CPU clock frequency, outperforms the A53 core in the Moto G (3rd gen) by a margin of 1.64x in the integer test and 1.93x in the floating point test, working out to 1.73x overall.

Having twice as many cores clocked at a higher frequency gives the ZenFone 2 similar performance to the iPhone 6 Plus in the multi-core test.

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Theoretical performance is good for bragging rights, but how a phone performs when running real-world scenarios is what truly matters. We already saw the ZenFone 2 claim victory in the AndEBench Pro Platform test, and now we see it rise to the top once again in PCMark, beating out the Galaxy S6 by a slim 9% margin.

The Galaxy S6 falls behind mainly due to its low Video Playback score, a test the ZenFone 2 has no trouble with. The Asus phone also does well in the Web Browsing test, outpacing the G4 but trailing the S6 by 16%.

Where the ZenFone 2 really shines is the Photo Editing test, performing 52% better than the second place S6. Most of the image processing during this test is supposed to occur on the GPU using the android.media.effect API. Monitoring the CPU and GPU core frequencies shows this is true for the ZenFone 2. Both the S6 and G4, however, appear to be using their CPUs instead, resulting in lower performance. It’s possible that only the ZenFone 2’s PowerVR graphics driver supports this feature.

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We use a static version of the Opera browser for Android testing to keep results comparable and avoid benchmark cheating. Unfortunately, the older version we’re using clearly does not like the x86 architecture. We’ve already seen that the Atom SoC in the ZenFone 2 performs competitively, so the abnormally low Opera browser results should be ignored.

With the Opera results compromised, we reran the tests using the stock browser app (JSBench did not work in this browser). These results show that the ZenFone 2 is more than capable of running JavaScript code. Note, however, that these results are not comparable to the other phones using Opera, since the stock browser app is newer and has a faster JavaScript engine.

So, what conclusions can we draw from our testing? The synthetic tests show that Intel’s Silvermont CPU core is roughly equivalent to an ARM A53 core at the same clock frequency, with Silvermont holding a slight advantage in floating point performance. Running its CPU cores at a higher frequency gives the Atom Z3580 a performance advantage over A53 based SoCs such as the Snapdragon 410 and 615 as well as most MediaTek SoCs, however. While it’s a strong contender in the mid-range market, Atom still cannot match the theoretical performance of Apple’s A8 or A57 based SoCs like the Exynos 7420 at the high-end of the market.

Ultimately, theoretical CPU performance is only part of the user experience equation. Running more realistic, mixed workloads that stress the entire system is when the ZenFone 2 rises to the occasion. Its combination of decent CPU performance, reasonably quick NAND reads, and a memory controller optimized for random memory accesses makes it feel like you’re using a flagship device that costs several hundred dollars more.