I mailed Dell with this question, but never got an answer. So now I'll try it here. Yesterday I had to restore a Windows 10 image on a Dell laptop. Unfortunately something went wrong and the Windows recovery tool had to format drives before restoring the image. Little did I know that it also deleted my data partition without asking. :-( Cost me whole night to gather the most important things from backups and syncs I luckily have. Anyway, it also removed the DIAGS-partition that is mentioned in this thread. Logical, since images are only made of the system and EFI partitions.
Windows 10 runs fine again now, but there is a nag in the back of my head. Is DIAGS necessary, does Windows do anything with it? I guess not, because this laptop originally came with Windows 8.1. Last year I did a clean install of Windows 10. I actually didn't even expect that the DIAGS partition would survive it. Anyway: should I be worried about the deleted DIAGS-partition in relation to the stability of Windows 10 or are they in no way related?
Follow-up question: the diags-tool from the bios is still working fine. What is actually he difference between both tools?
The laptop is an Inspiron 7537, to be exact. :-)
If you are referring to the ePSA diagnostics menu accessible from The Dell logo screen by accessing the one time boot menu (Fn+power on) then you do not have to worry. Windows should not have the capability to delete the diagnostics utility. This is present whether the system has a hard drive or not.
If you are referring to the the window recovery partition when you tried to reinstall windows. It should be there as well.
In the scenario that you have deleted/ formatted the drive completely, each time windows installs it would create a recovery partition which would allow you to repair the computer if the need be.
However, there is a chance that the windows recovery image might get delete or not saved during a windows 10 install, which you leave the system incapable of a reset or a refresh without the windows 10 media. As long as the media is available online, there is no need to worry.
The BIOS utility lets you configure Pre-OS environments and how some hardware should function. It also lets you choose the Boot sequence. If the BIOS gets corrupted, you will either have a no boot scenario or you will not be able to access the BIOS.
The ePSA or the built-in hardware diagnostics tool is independent of the BIOS as well and exists only to to check the functionality of certain hardware on the system.