Q. Physical Address Extension (PAE) refers to a feature of x86 and x86-64 processors that allows more than 4G bytes of physical memory to be used in 32-bit systems. The x86 architecture presently uses only 36 bits out of 52 bits possible. On x86-64 processors, PAE is obligatory in native long mode; currently 40 bits are used out of 52 bits possible. How do I find out if my Linux kernel supports 36-bit or more physical addressing?

A. You can easily find this information by visiting /proc/cpuinfo file. cat /proc/cpuinfo and look for the physical address size. You can also use grep command extract exact information:
cat /proc/cpuinfo
OR
grep physical /proc/cpuinfo
Sample output:

physical id	: 0
address sizes	: 36 bits physical, 48 bits virtual
physical id	: 3
address sizes	: 36 bits physical, 48 bits virtual
physical id	: 0
address sizes	: 36 bits physical, 48 bits virtual
physical id	: 3
address sizes	: 36 bits physical, 48 bits virtual