The IBM System x computers form a sub-brand of International Business Machines (IBM's) System brand servers (the other System sub-brands having the names IBM System i, IBM System p, IBM System z and IBM System Storage). In addition IBM System x is the main component of the IBM System Cluster 1350 solution.
Starting out as IBM PC Server, rebranded Netfinity, then eServer xSeries and now System x, these servers are distinguished by being based on off-the-shelf x86 CPUs; IBM positions them as their "low end" or "entry" offering.
Note: Previously IBM servers based on AMD Opteron CPUs did not share the xSeries brand. Instead they fell directly under the eServer umbrella, however, AMD Opteron-based servers now fall under the System x brand.
