Linux can use memory (RAM) which it should not (?) see
I have a question about GNU/Linux. My laptop has 6GB of RAM, and I have installed Linux Mint 17.2 x86 on it. From my knowledge, 32-bit OSes can handle only 4 GB, but Linux Mint reports that it can use all of 6 GB.
How is that possible?
Physical Address Extension (PAE), sometimes referred to as Page Address Extension, is a memory management feature for the IA-32 architecture. PAE was first introduced in the Pentium Pro. It defines a page table hierarchy of three levels, with table entries of 64 bits each instead of 32, allowing these CPUs to access a physical address space larger than 4 gigabytes (23^2 bytes).
(c) https://en.wikipedia.org/wiki/Physical_Address_Extension
Physical Address Extension (PAE) is a feature found on almost all 32 bit processors produced after Pentium Pro, ie. younger than around 1995. Because PAE is close to being a standard it is now a requirement for Ubuntu: During installation the processor is prompted for the PAE flag, and only if present the process will carry on.
Lubuntu and Xubuntu offered a PAE and a non-PAE release up to and including 12.04, but from 12.10 only the PAE releases are maintained.