A Look at What Has Changed from the Snapdragon 820 to the Snapdragon 821 in the Google Pixel Phones

We reached out to Qualcomm to get a better look at the Snapdragon 821 processor that is making an appearance in the upcoming Google Pixel and Pixel XL, the Asus ZenFone 3 Deluxe, the Xiaomi Mi 5s, and the LeEco Le Pro 3. With the Snapdragon 821 in the Pixel phones running at the same clock speed as the regular Snapdragon 820, many people were asking what benefits the new SoC brings, and why choose it if they’re not going to use the higher clock speeds it can bring.

Our interest was piqued when the Android Platform’s Performance Lead mentioned that Google was not underclocking the Snapdragon 821 (contrary to popular belief), and thus implied that rather the version that they were using came running at the same speeds as the main version of the Snapdragon 820 by default.

The short version is that not much has physically changed in the design of the Snapdragon 821 from the 820, but we were able to make some interesting discoveries in the process. The Snapdragon 821 is a revision similar to the Snapdragon 801 and 800, and is brought about primarily by improving yields.

These improved yields have allowed Qualcomm to release essentially a revision of the Snapdragon 82x that can either use 5% less power at the same clock speeds as the original version, or be tuned for slightly higher clock speeds at around the same power usage as the 820. This follows closely in the footsteps of the Snapdragon 800 and Snapdragon 801, where the improved yields allowed Qualcomm to release a slightly improved version of the 800 halfway through their regular development cycle.

Qualcomm informed us that there are indeed two revisions of the Snapdragon 821. One running at the advertised maximum CPU and GPU clock speeds of 2.34 GHz and 653 MHz (respectively), and a separate one running at the same 2.15 GHz and 624 MHz that was found in the main Snapdragon 820. The Pixel phones are using the later one, which we have been informed is called the MSM8996 Pro-AB. While we have not yet been able to get confirmation about the name of the higher clocked model, if it is following the same model as the Snapdragon 800 and 801 chips, it may be either the MSM8996 Pro-AA or the MSM8996 Pro-AC.

One thing to note is that despite rumors to the contrary, Google did not pick the Snapdragon 821 because of the Snapdragon VR SDK. While definitely a nice tool, it works on both the Snapdragon 820 and 821, and is not a distinguishing feature between the two chips.

With how heavily Google was pushing the improvements to the Pixel phones’ camera, we thought there might be some Image Signal Processor improvements, and at first glimpse there appeared to be, with the Snapdragon 820 being listed as being capable of processing 25 MP images at 30 Hz, and the Snapdragon 821 being listed as being capable of processing 28 MP images at 30 Hz; but that turned out to be a typo, which has since been corrected. The Qualcomm Spectra ISP in both SoCs are capable of processing the same 28 MP at 30 Hz.

Instead, Google sought out improvements to their HDR+ processing speed by finding ways to better leverage Qualcomm’s Hexagon DSP, through the use of Qualcomm’s Hexagon Vector eXtensions. Google is offloading substantial portions of processing for HDR+ to the Hexagon DSP that used to be handled by the CPU itself, and that has played a major role in both decreasing the time it takes to process HDR+ shots, and in allowing the Pixel phones to continue shooting HDR+ shots, with DXOMark finding that it could shoot one HDR+ shot every three seconds indefinitely. This pairs very well with the faster shooting capabilities brought about by the Sony Exmor RS IMX378 image sensor to create an exceptional camera.

While not directly related to the processor itself, Google has mentioned that they have put substantial work into helping improve the scheduler found in the Pixel phones, which is fantastic news as schedulers are, in the words of John Poole, “horrendously complicated pieces of code”, and small improvements can have major impacts on real world performance.

Overall, the Snapdragon 821 should be a solid revision, but if you’re looking for a big jump in performance, you’re going to have to wait a couple more months to see the real next generation of chips start appearing in flagship phones next year (the rumored Snapdragon 830), which Qualcomm just announced will be using their new X16 LTE Modem. The new modem is particularly interesting, as it will bring some substantial improvements like LTE Dual SIM Dual Active, Category 16 and 13 downlink and uplink, multi-carrier 4×4 MIMO, 4×20 Carrier aggregation, and a theoretical peak download speed of 1 Gbps.

What do you think of the Snapdragon 821? Are you excited for its use in the Pixel phones, or are you rather anticipating next year’s flagships with the Snapdragon 830 and the X16 LTE Modem?

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