Why is the used Intel HD Graphics 530 video memory and the amount of RAM displayed incorrectly?

Question

BIOS

Hello. In general, there is the following pitch:
Intel i5-6400 2.7GHz
RAM 16gb(2x8gb) dual channel
MSI h110m pro-vd
Windows 10 x64
The problem is the following - in the BIOS there is such a parameter as allocated memory for the video card. There are two questions about it:
1. First, why is there a maximum of 1024 MB? Judging by the specifications of the Intel HD Graphics 530, it can have much more memory.
2. Secondly, why, despite the fact that I set this value to 1024 MB in the pitch settings and in profile applications, is there a default (minimum) value of 128 MB?
3. Thirdly, yesterday I literally bought a second RAM slot, inserted it in all applications and the BIOS now shows that I have 2 8GB slots and dual channel mode is working, but in the adapter settings I still see "General system memory 7657 MB ":

GPU-Z (after installing the second RAM slot):

GPU-Z (before installing the second RAM slot):

AIDA single channel:

AIDA dual channel:

Task Manager:

That is, everything is up and running correctly, but somewhere - then, apparently, there is still a problem.
Thanks in advance for your replies.

Answer 1

We take the calculator 7785 (available memory that the video core can use) minus 128 MB (the core is using right now) is equal to 7657 (still potentially available memory for the video core, but most likely only 1024 MB will be taken from here as set in the BIOS, just Windows, this limitation is not knows, or rather knows, but in this case it displays how much could potentially be allocated, if not for BIOS restrictions)
Now the task manager. From 16GB a little lower, we see what is available to the system 15GB and it is correct, since Bios reserved 1024MB for the video core and here Windows knows about it because everything displays correctly.