iSeries is IBM's midrange server line, designed for small businesses and departments in large enterprises. The product line, formerly known as AS/400 (still the preferred name among many long-time users ), was renamed in 2000 with the introduction of the V5R1 operating system and 800 line of servers. i5 is the latest hardware evolution of one of IBM's most widely-installed product lines. iSeries servers use IBM's Power5 microprocessors and are capable of running five different operating systems at the same time (AIX, Windows, Linux, OS/400, and i5/OS) on multiple partitions. IBM also offers p5 (or pSeries) servers for large enterprise users who want to run Unix systems or who need more scalability.
According to Chief Scientist IBM iSeries, Dr. Frank G. Soltis, the iSeries is used by businesses all over the world, is sold in more countries than McDonald's hamburgers, and has the largest number of customers of any IBM server.
Search400.com expert John Brandt explains the advantages of upgrading from AS/400 hardware to the i5: