AS/400, a name commonly associated with IBM iSeries, is a mid-tier server designed and developed for small-business environments or single sectors of big companies. Modified and updated at a later time in order to work on distributed networks with Web applications, the AS/400 uses PowerPC processors with a limited set of instructions and the OS/400 operating system.

AS/400 has been a milestone in the IBM history and its success has been determined by the high levels of reliability and stability both from an hardware and from a software basis, coupled with a relatively low price (almost 20.000€) and with the ability of managing hundreds of terminals at the same time.