The AS400 family of business-oriented computer systems is an IBM product line first introduced in 1988 for use in security-critical applications that require multitasking and multiuser access. AS400 systems also include integration with IBM's DB2 database system. While the AS400 product line was renamed several times during its lifetime, the name AS400 has remained the most popular term for referring to this type of computer system and its descendants.
The AS400 and its derivative eServer iSeries and Power series descendants are classified as mid-range computer systems intermediate between mainframe and microcomputer designs. AS400 machines and their descendants use the IBM i operating system but can also run the AIX and Linux UNIX derivatives as well as Microsoft's Windows Server family operating systems. AS/400 systems largely use POWER-based RISC CPUs, though the first generations of the system used a proprietary IBM processor similar to the IBM 370 chip.
Many AS/400 tasks are performed using the IBM Control Language, a scripting programming language that allows for both system-level task management and user programming. Control Language scripts are similar in principle to shell scripts in DOS or UNIX systems, though the syntax of Control Language is different from either of those operating systems and it is not limited to system tasks. Commands in Control Language are superficially similar in format to those of Structured Query Language, and new commands can be implemented and utilized by other users of the system.