64Gb RAM on Gigabyte Z170 MB, GTX 980 Ti, Only 61.6 Usable RAM

I know the "Hardware Reserved" memory topic has been discussed many many times, but I read through many posts, people who experience this problem often report that they have unusually high reserved memory, which is different from my case.

I have a Gigabyte Z170X-UD5 TH motheboard, 64Gb RAM, with a nVidia GTX 980 Ti. I am not using the onboard Intel Graphics, and as far as I can tell, I have disabled the only line related to it in the BIOS. In Windows 10, the System control panel reports that there is 64Gb RAM, but only 61.6 Gb is usable. The Task Manager shows that the 2.4 Gb RAM is "Hardware Reserved".

According to many posts I read, and Microsoft's own website, it is NORMAL for the OS to reserve some RAM for hardware usage. That, I have no problem with. However, when I checked my Windows 8.1 machine (64 bit), its System control panel reports that all my 8Gb RAM on that machine is available -- although, that machine's Task Manager does show that 1Gb RAM is hardware reserve.

My question is, is it normal? 2.4Gb out of 64Gb is not a not, and if it's reserved for hardware, I have no problem with that. But, why doesn't my old 8.1 machine's System control panel report the same condition while it also reserves 1Gb for hardware usage? From what I can tell from posts eightforums, even older Windows OS's System control panel would deduct the reserved memory out from the usable RAM.

I just checked on my desktop and laptop - both running Win10 x64. The desktop is an Asus P9X79 mobo with 32Gb RAM, no onboard video, and Task Manager shows hardware reserved memory as 58Mb. On the ASUS UX32VD laptop (10Gb RAM), which has both Intel and nVidia graphics adapters, both enabled and with drivers loaded, hardware reserved memory is 114Mb.

What you are seeing is normal. The CPU has a MAX memory address space of 64GBs. However the same address space is used for addressing hardware thus you cannot fully utilize it for memory. When you fill up the address space, the hardware reserve is eating into your memory, otherwise it would just eat into address space.