This week was pretty exciting for Windows Insiders as Microsoft surprised users by releasing not one, but two Windows 10 previews. While the software maker rolled out Windows 10 build 10158 to the Fast ring of updates on June 29th with a number of improvements and various visual changes, the company also released Windows 10 build 10159 on June 30th, which the company says includes over 300 bug fixes.

Why did Microsoft suddenly release a new build? According to the company, it validates every build it produces internally, and builds are tested by engineers "OSG and Microsoft". If the build passes all the tests, the company rolls out the bits to Windows Insiders. First they become available to the Fast and finally to the Slow ring of updates when is stable enough. And as we all know, Microsoft isn't just working with a single build. It's always working with multiple builds, and Windows 10 build 10158 and build 10159 just happened to pass all the tests to be available to the public.

So, what's new in Windows 10 build 10159? Well, as it turns out the major changes included in the new preview is a tweak in the login screen, which now features a centered design with a circular image. Before, the profile picture was aligned to the left with the box to enter the login credentials to the right.

Also the login screen, not to be confused with the Lock screen, now features the new default Windows 10 "Hero" image which Microsoft showed off on a new video a few days back.

Also, if you're upgrading a preview without a custom background image you have previously set, you'll now also see the new Windows 10 "hero" image as the default background on the desktop.

Quick Tip: If you like the new wallpaper Microsoft has created, you can browser the following path "C:\Windows\Web\4K\Wallpaper\Windows" to extract the wallpaper, so you can use it on any device, including in Windows 8.1. It's worth pointing out that Microsoft is not just including one, but multiple sizes of the same image to accommodate all the screen sizes Windows 10 will support. (Source Twitter)

The other changes are happening under the hood. Microsoft says it has included hundreds of bug fixes in build 10159, so this new build should be more stable. The company has not released any specific details.

Microsoft also warns that users may run into the error 0x80246017 if you happen to be downloading 10158 when 10159 is being rolled out. If you see this error, simply restart your PC and downloading the update once again.

As you can see, there is not much new in this particular build, however Windows 10 build 10158 is packed with changes, improvements, and a few new features, such as tweaks to the Start menu, taskbar, and flyouts. There are also a few improvements on Tablet mode, where users will see quick access to the "Power" options and "All apps". Cortana, Settings app, and Microsoft Edge also receives some interesting improvements. Also, Windows Insiders can now test the Phone Companion app and a lot more.

Check out everything that is new in Windows 10 build 10158.

Do you think Microsoft made the right choice by delivering a new build this quickly? Tell us what you think in the comments below.