The IBM System i includes an operating system originally known as OS/400, later as i5/OS and IBM i. System i is also capable of supporting multiple instances of AIX, Linux, Lotus Domino, Microsoft Windows 2000 and Windows Server 2003. While OS/400, AIX, Linux and Lotus Domino are supported on the POWER processors, Windows is supported with either single-processor internal blade servers (IXS) or externally linked multiple-processor servers (IXA and iSCSI). iSCSI also provides support for attachment of IBM Bladecenters. Windows, Linux, and VMware ESX(VI3) are supported on iSCSI attached servers.