Windows 10 Mobile was just launched without too much fanfare on Microsoft's part and many users have started the upgrade process from Windows Phone 8.1. However, this upgrade won't mean just a new look and new and exciting feature s. Unfortunately, it will also mean a few bugs and performance issues. We took two smartphones with very different hardware, installed both operating systems on them and then compared the performance offered by each operating system, using several tests and benchmarks. Here's what we have learned:

Windows 10 Mobile vs. Windows Phone 8.1 - The performance comparison

We are two colleagues wh o worked on this comparison in parallel. One of us had a Nokia Lumia 930 with Windows Phone 8.1 and the other had a Microsoft Lumia 640 with Windows Phone 8.1. These two smartphones are very representative for the Windows Phone ecosystem, both in terms of features and popularity. The Lumia 930 is the most powerful smartphone with Windows Phone 8.1 while Lumia 640 is one of the most affordable and popular Windows Phone device s. We are both based in Romania, in different cities, and we use different cellular providers. We both ran the same tests, in the same order, before and after making the upgrade to Windows 10 Mobile.

Your smartphone's startup time - Winner: Windows Phone 8.1

As you can see, in the chart below, Windows 10 Mobile adds quite a lot to the startup time of your smartphone. Microsoft Lumia 640 started 28% slower when Windows 10 Mobile was installed, while Lumia 930 was 33% slower during the startup procedure.

The impact Windows 10 Mobile has on your smartphone's startup time is very large when compared to Windows Phone 8.1.

Web browsing speed - Winner: None

Many people browse the web on their smartphones on a daily basis. That's why we considered it important to run a quick web browsing benchmark: SunSpider. As you can see below, Windows 10 Mobile was slightly slower on the Lumia 930 (by 6%) and slightly faster on the Lumia 640 (by 2%).

These results don't allow us to draw a clear conclusion. When it comes to the web browsing speed , your experience should be similar on both operating systems. However, the web browsers are different in Windows Phone 8.1 and Windows 10 Mobile and they offer different features. It is very likely that you will appreciate Microsoft Edge from Windows 10 Mobile more than Internet Explorer from Windows Phone 8.1.

The speed of your data connection - Winner: Windows 10 Mobile

The two smartphones we have used for comparing Windows 10 Mobile with Windows Phone 8.1, worked on different telecom providers, from different geographical locations. On the Lumia 640 we had a good 4G data connection while on the Lumia 930 we had only a 3G data connection. We used SpeedTest to see which operating system is able to deliver faster downloads and uploads on the Internet.

When measuring the download speed, there is no clear winner. The differences we have noticed are small enough not to be noticed during regular use.

When measuring the upload speed on the Internet, Windows 10 Mobile managed to be faster than Windows Phone 8.1 on both smartphones and cellular connections.

Next, we wanted to measure the performance offered by the two operating systems when running apps, writing data into the RAM memory or the storage space, how efficiently they used the graphics chips on the two smartphones, and so on. In order to do that, we ran several benchmarks.

WP Bench benchmark - Winner: Windows Phone 8.1

We began by running the WP Bench benchmark on both smartphones. It tests the speed of the processor, the graphics chip, the memory and the storage on your smartphone. First, let's take a look at the result obtained in the CPU tests. In these tests it is important to obtain a lower score. The lower the score, the faster is the operating system in working with the smartphone's processor.

On the Lumia 640, Windows 10 Mobile was 9% slower than Windows Phone 8.1 while on the Lumia 930, it was 3% slower.

It seems that, on lower-end devices with less powerful processors, Windows 10 Mobile is slower than Windows Phone 8.1 when working with the CPU. On high-end devices with more powerful processors, the difference isn't meaningful enough to be felt in normal use.

Then, we looked at the results obtained in the other tests offered by WP Bench : memory, storage and graphics. We also looked at the general score measured by WP Bench , so that we can compare the performance offered by the two operating systems.

As you can see below, on the Lumia 640, Windows 10 Mobile was 6% slower than Windows Phone 8.1.

On the Lumia 930, Windows 10 Mobile was, again, 6% slower than Windows Phone 8.1.

According to the WP Bench benchmark, the performance offered by Windows 10 Mobile is 6% lower than that of Windows Phone 8.1 on the same smartphone.

Multibench 2 benchmark - Winner: Windows Phone 8.1

The Multibench 2 benchmark evaluates the speed of your smartphone's processor, data transfers, memory transfers and that of the graphics chip. On the Lumia 640, the situation is as follows:

• Windows 10 Mobile was 3% faster than Windows Phone 8.1, in the processor test. This conflicts with the results obtained in the WP Bench CPU tests and confirms the results we have seen in SunSpider. The only fair conclusion to draw is that, most probably, there's no speed gain in working with the CPU, when using Windows 10 Mobile versus Windows Phone 8.1.
• Windows Phone 8.1 was 16% faster than Windows 10 Mobile in transferring data to and from the storage space.
• Windows Phone 8.1 was 10% faster than Windows 10 Mobile in the memory test.
• Windows Phone 8.1 was 396% faster than Windows 10 Mobile in the graphics test. This result sounds to o good to be true and most probably, the way the Multibench 2 calculates its results in Windows 10 Mobile needs to be updated so that it returns more realistic results in Windows 10 Mobile.

On the Lumia 930, the situation is as follows:

• Windows 10 Mobile was 2% faster than Windows Phone 8.1 in the processor test.
• Windows Phone 8.1 was 20% faster in the data transfer test.
• Windows Phone 8.1 was 6% faster in the memory test.
• Windows Phone 8.1 was 362% faster in the graphics test. Again, this is most probably a calculation error in Multibench 2 and the benchmark needs to be updated so that it better reflects the true performance of the graphics chip in Windows 10 Mobile.

Multibench 2 tends to confirm some of the results obtained with the WP Bench benchmark, which state that Windows Phone 8.1 is more efficient in using your smartphone's hardware to deliver the performance you need.

AnTuTu benchmark - Winner: Windows Phone 8.1

AnTuTu is another benchmark that evaluates lots of things, including: the memory, the processor, the 2D graphics, the speed of the storage space and so on. It separates its data into lots of complicated subscores which are hard to follow but it also provides a general score which we used for comparison.

As you can see below, on the Lumia 640, Windows 10 Mobile was 7% slower than Windows Phone 8.1 while on the Lumia 930, Windows 10 Mobile was 6% slower than Windows Phone 8.1.

The AnTuTu benchmark shows one more time that Windows 10 Mobile offers less performance on the same smartphone than Windows Phone 8.1.

Battery time - Winner: None

We know that battery time is an important aspect for every smartphone user. That's why we have run the WP Bench battery test which stresses the smartphone to the maximum until it drains all its battery. As you can see below, on the Lumia 640, Windows Phone 8.1 lasted 3 minutes more than Windows 10 Mobile, while on the Lumia 930, Windows 10 Mobile lasted 7 minutes more than Windows Phone 8.1.

From these results it is obvious that there is no important difference between Windows Phone 8.1 and Windows 10 Mobile when it comes to battery-life. The two operating systems drain your smartphone's battery in just about the same time.

Conclusion: Windows Phone 8.1 is faster than Windows 10 Mobile

This should not be a surprise to most users: Windows Phone 8.1 is a highly optimized operating system, which makes great use even of the slowest smartphone hardware. Windows 10 Mobile has a long way ahead until it reaches the same level of polish and performance. In return for new features and some lost features, you get a much longer startup time and less performance, especially on low-end smartphones with less powerful hardware.