One of the main reasons the AS/400 is such a popular system, with over 250,000 systems installed, is that there is a very broad spectrum of application software available for the AS/400. As a result, many enterprises depend on AS/400 based on-line transaction processing systems for the day-to-day operation of their business.
For some time, these systems were used for such OLTP applications exclusively. As the business grew, the processing volumes on the AS/400 grew. Generally such growth was not spectacular, but gradual and continuous. The AS/400 systems were operating at or near processing capacity, but there always seemed to be room for "a little more" growth.