CentOS is an enterprise Linux distribution based
on the sources from Red Hat Enterprise Linux.
CentOS conforms with Red Hat's redistribution
policy and aims to be 100% binary compatible. Each
CentOS version is supported for 7 years (by means
of security updates). A new CentOS version is
released every 2 years and each CentOS version is
regularly updated (every 6 months) to support
newer hardware. Currently, there are 4 different
supported CentOS releases: CentOS-5 is based on
Red Hat Enterprise Linux 5, CentOS-4 is based on
RHEL4, CentOS-3 is based on RHEL3, and CentOS-2 is
based on RHAS2.1.