OpenClinica Enterprise is available either via a cloud hosted solution or a self hosted and managed system. The base supported platform for self hosted customers is Red Hat Enterprise Linux (RHEL) 6.5 or above. RHEL is a commercially supported operating system and recommended for enterprise customers. CentOS is a free rebuild for RHEL without commercial support and is available at http://centos.org. For either, we highly recommend using the 64-bit version for best performance if your hardware is capable of supporting that architecture.