MemTest86 tests more RAM than exists

[emc]

Specs:
Motherboard Asus P8Z68-V Pro
CPU Intel i5 2500K
RAM Corsair CMX8GX3M2A1600C9 2x4GB

I'm using memtest86 from USB UEFI (V7.1), it shows me 8247M of RAM and tests up to adress 0x21F000000, no errors.
The UEFI Bios is showing me 8192 MB of RAM.
Booting from the USB stick in non UEFI mode starts memtest86 V4, which tests only 8152 MB RAM.

Why does the uefi v7 show mroe RAM than there should be? And tests to a higher adress (max should be 0x200000000)?

The lower amount of tested ram in v4 probably is a result of bios-locked RAM?

[David (PassMark)]

Memory addresses can exceed the physical RAM because some addresses are reserved for other devices.

See this page on Memory mapped I/O for details.

This mapping differs in BIOS compared to UEFI. You can actually dump out the memory map from the "System Info" function in MemTest86 V7.