I have a question regarding the 100MB partition in Windows7 - Windows10
Is the 100MB partition in Windows 7-Win10 , there regardless of whether the drive's partition table is MBR or GPT?
There are two different partitions that you might be talking about (System and MSR). Windows 7-10 use a "System" partition which contains the boot manager. Having the boot manager on a separate partition makes it so that the operating system partition can be encrypted (using Bitlocker), and the boot manager (on the non-encrypted system partition) can unlock the operating system partition (decrypt in-memory) before booting into it.
The MSR (Microsoft Reserved) partition is only used on GPT installations. I'm not sure what this is for.