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.