Your Windows 10 Mobile questions answered: 920 vs 435, Dual core S4 vs Snapdragon 200

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By popular request, and following the announcement by Microsoft that the low end Lumia 435, 532/535 (etc.) are approved for the Windows 10 Mobile update (and beyond), but not yesteryear's flagships, such as the Lumia 920, 925 and 1020, with the older generation of S4 processors, I put two devices head to head running the production version of Windows 10 Mobile - how does performance stack up and were Microsoft right to exclude the older phones? Or should they have included less phone upgrades in the mix?

For the purposes of this feature I'm using the Lumia 435 (representing the lowest of the newer 'approved' budget phones) and Lumia 920 (representing the older 'not approved' Snapdragon S4-powered flagships from 2012 and 2013). The comparison should be pretty fair - after all, both devices have the same amount of RAM, both were upgraded to the Threshold Release Preview build (currently 10586.164, or at least it was when I started this feature!) and the most obvious other factor is the lower 480p screen resolution on the budget phone (the 920 is 768p).

For comparison, I'm also looking at the slightly more capable Lumia 640, with two extra processor cores - how much difference will this make? And finally, as a baseline for how fast the experience should be, I've included figures for the Lumia 950 as well.

From left to right, Lumia 950, 920, 435 and 640

From left to right, Lumia 950, 920, 435 and 640

So we're mainly looking at the differences in chipset here. Common sense tells me that the 'flagship' 920 should be quicker and smoother than the bottom end 435, but on othe other hand I've said for well over a year now that much of the Windows 10 code and applications are optimised for the x00-series chipsets. So this could be a close fight, after all...

Note that all times are in half seconds, first time launches only, where appropriate. And each test was done several times, with the fastest being recorded here - obviously there's some variation according to data transferred, network conditions, and so on. Which is also why there's zero point in me timing things more accurately than done here...

Windows 10 Mobile

Lumia 950 (3GB RAM) Lumia 920 (1GB RAM) Lumia 435  (1GB RAM) Lumia 640

Snapdragon 808
Hexacore, up to 1.82 GHz

Snapdragon S4 Plus
Dual-core 1.5 GHz Krait

Snapdragon 200
Dual-core 1.2 GHz Cortex-A7

Snapdragon 400
Quad-core 1.2 GHz Cortex-A7
Booting up to Start screen 35 43 44 37
Opening up Outlook Calendar 1 2.5


Bringing up the day's weather
in MSN Weather
2.5 3.5 4.5 3
Launching MSN News to
opening graphics
3 4.5 5 3
Opening up Outlook Mail 1.5 2.5 2 2
Opening up Skype
i.e. signing in after boot 
7 8 9 7
Opening up Cortana to the
'look at the day' vertical
panorama, after boot
4.5 7 11
Opening the full New York
Times desktop web site to
the filling in of the
right side bar content
9 33 24 33
Starting Camera (first time) 2 3.5 3.5 2
Time taken to analyse
built-in storage*
7 (for 32GB) 6 (for 32GB) 8.5 (for 8GB) 4 (for 8GB)
Opening the Music Store
from Groove Music
3.5 7 9.5 4
Total (seconds)
(lower is better!)
76 120.5 123 102.5

* this depends on the size of the storage, of course. The 32GB devices (e.g. 920) will obviously take longer. Also, the 950 here was loaded to the gunnels, while the other three devices were largely empty.

In terms of analysing the results, a look at the bottom line totals tells us that the Windows 10-approved Lumia 435 was actually slower overall than the non-Win-10-approved Lumia 920, in line with my gut feeling above, though there wasn't a lot in it. The biggest win for the Lumia 435 over the 920 was in the Edge browsing speed, with the lower screen resolution no doubt easing the calculation burden when rendering. Take away the browsing score, mind you, and everyday operations and the UI in general on the Lumia 920 was about 10% faster.

So why on earth was the 920 (and 925, 1020, 820, et al) not deemed worthy of the Windows 10 Mobile update? I have a theory. You just knew that I would.

The problem is that Windows 10 Mobile, no matter what anyone says, is slower and more resource hungry than Windows Phone 8. Of course it is - there's lots more code, much of which originated in the more powerful desktop environment. I'd say a factor of two slower than the older OS. Meaning that to run Windows 10 Mobile at a fast enough pace you need something meaty under the hood. I was proved right (and then some) in my predictions that 1GB of RAM would be the baseline for Windows 10. But you also need a fast processor, ideally with at least four cores (for all the parallel processing that the OS and applications can then do).

The Lumia 950, above, has a Snapdragon 808 chipset plus 3GB RAM and is plenty fast enough, I'd say that Windows 10 Mobile runs (in terms of applications and UI) at a speed that's comparable to most decent Android handsets and iPhones. The Lumia 930 and 1520 ditto, a Snapdragon 800 chipset and 2GB of RAM, you don't really notice any drop-off in speed from the latest 950 range, and I'd expect that (bugs aside) just about every Windows Insider trying the new OS on the 930/1520 would have given it a general thumbs up. So a no-brainer for Microsoft to green light these devices to receive the official Windows 10 Mobile upgrade.

But then we come to older and less capable devices. And in terms of enthusiasts, which is what Insiders most definitely are, devices like the 920 (above), 925 and 1020 were very, very popular over the last couple of years. I'd guess that as much as a quarter of all Insiders feedback given to Microsoft was on these handsets. Now, Windows 10 Mobile is not unusable on these Snapdragon S4-powered, 1GB RAM devices, as the times and scores above prove. We're talking around half the speed of the 950/930/etc. In other words, for a patient enthusiast, an older device like the 920 might be perfectly serviceable. But you can bet that, when asked about the speed (and stability) of the 920 under the Windows 10 Mobile Insiders builds, users will have made some negative comments, and rightly so. The experience is simply not up to 2016 levels of slickness.

So Microsoft got feedback from 920, 925 and 1020 owners criticising the speed of Windows 10 Mobile. And a lot of it, because of the skew to these models in the programme. And so the decision was made to exclude these (and lesser models in the range, so 720, 820, 620, 520 and variants).

But, you exclaim, what about the Lumia 435 above? You proved in your tests that the Lumia 920, slowish though it is under Windows 10 Mobile, is still faster by a significant margin than the Lumia 435 - which IS supported for the Windows 10 Mobile upgrade!

The thing is that the Lumia 435 was a very slow handset under Windows Phone 8.1 - it has bottom end specifications, from chipset to touchscreen quality and this shows in the UI and experience. Under Windows 10 Mobile it's even slower and I'd argue that if a similar number of Lumia 435 users gave Insider feedback to Microsoft then the 435 would most definitely have not been approved. As it was, I suspect they got hardly any data points on the 435 - it's not exactly (ahem) an enthusiast's device, and so had to go on internal testing, which showed that the 435 could run the OS, at least. And even now, the number of low end 435 owners who happen to find out about the Windows 10 Upgrade Adviser and try the upgrade is going to be vanishingly small.

And so on up the chain we go. Snapdragon 400 and 210 chipsets mainly, running Windows 10 Mobile at a speed and experience somewhere in between the fastest (930/950) and slowest (920/435) handsets. You can see from the scores above. I've only really considered a few data points, but I'd estimate that using, say, an upgraded Lumia 640, 735 or 830 will only involve a 40% speed hit from the fastest devices - and that's probably acceptable, given all the 'pros' for upgrading. Users of such mid-range devices wouldn't be expecting flagship speed anyway, so these made for positive feedback and a 'yes' from Microsoft.

In short then, the Lumia 920 (et al) IS faster under Windows 10 Mobile than the bottom end Lumia 435. But rather than query why the 920 didn't get the nod from Microsoft, I'd question why the 435 did. I'd have left it on 8.1, where at least its UI and apps speed is vaguely tolerable!

Comments welcome, as always!

PS. extra reading for you over on Reddit, where a theory about GPUs and screen resolutions tries to defend the 435-but-not-920 decision.