"Nowadays, many machines are running with 2-4 gigabytes of RAM,
and their owners are discovering a problem: When they run 32-bit
GNU/Linux distributions, their extra RAM is not being used.
Fortunately, correcting the problem is only a matter of installing
or building a kernel with a few specific parameters enabled or
"The problem exists because 32-bit Linux kernels are designed to
access only 1GB of RAM by default. The workaround for this
limitation is vaguely reminiscent of the virtual memory solution
once used by DOS, with a high memory area of virtual memory being
constantly mapped to physical addresses..."