Got more than a gig of RAM and 32-bit Linux?

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 disabled.

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. This high memory can be enabled for up to 4GB by one kernel parameter, or up to 64GB on a Pentium Pro or higher processor with another parameter. However, since these parameters have not been needed on most machines until recently, the standard kernels in many distributions have not enabled them.

Increasingly, many distributions are enabling high memory for 4GB. Ubuntu default kernels have been enabling this process at least since version 6.10, and so have Fedora 7's. By contrast, Debian's default 486 kernels do not. Few distros, if any, enable 64GB by default.

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