How Can I Identify my Build Number?

[Ivan Kim Reyes]

I am really confuse about the mobile build number thingy. I really don't know where to find it. I am using Lumia 540 with GDR2, OS Version 8.10.15137.148. I have read that mobile build is the OS version itself. But I don't understand how you people -tech savvy people- most of the mobile builds shown on search engines and in youtube shows mobile build number that I think far different than the OS version number. I don't know what mobile build I have.

 

[Zachary Boddy]

You're running Windows Phone 8.1 Update 2 it looks like. The first number (8) is the operating system version (Windows 7, 8, 10, etc.), and the second number refers to major updates like Windows Phone 8.1. That's not the best explanation but it's enough. The third set tells me you're running Update 2, or GDR2. You're probably running Lumia Cyan firmware but could be running Lumia Denim.

Windows Phone 8 was the major operating system version. It's to Windows Phone 7 what Windows 10 Mobile is to Windows Phone 8. Basically a new operating system.
The .1 is a major update. It added the Action Center and Cortana. Very important update.
The third set refers to kinda major updates. Like GDR2, which gave you the revamped Settings menu.

Now my knowledge is far from perfect and someone can probably give you a better explanation and probably teach me some things too, but I hope I helped!