In old 32 bit systems, the max addressable amount of RAM was 4Gb. Now you need memory space in order to communicate with hardware on the computer, so at the end of the 4Gb, space was reserved that doesn't tap into memory, but taps into devices. I think the memory space for devices is now much higher on 64 bit systems with good drivers and new hardware so it doesn't get in the way of RAM.
However, even 64 bit systems can still have devices and drivers that use that space under 4Gb for legacy reasons. Some newer systems with good devices, drivers and BIOS' use very little hardware reserved memory. (around 29Mb Hardware reserved by my 5Gb (yes 5) Dell laptop.)
Sometimes you can change BIOS settings to get more memory. Some BIOS' offer software memory hole remapping.
Having hardware reserved memory will not benefit your system in any way and is only a detriment as you have memory that cannot be used.