CentOS ("Community Enterprise Operating System") is a Linux distribution that attempts to provide a free enterprise class computing platform which has 100% binary compatibility with its upstream source, Red Hat Enterprise Linux (RHEL). As of versions 5.10 and 6.5, CentOS officially supports the x86 architecture with Physical Address Extension (PAE) and the x86-64 architecture, while a beta release is expected to be available for the PowerPC architecture.The first CentOS was based upon RHEL version 2.1AS, and was numbered as CentOS version 2.