AS/400 is a mid-range computer. A Midrange computer, or midrange system, is a designation used mainly by IBM for a class of computer systems which fall in between mainframe computers and microcomputers. The range was developed in 1960s and more generally known at the time as minicomputers (a term obsolete since 1990s). Popular makers of such computer lines included for example Digital Equipment Corporation (PDP line), Data General, Hewlett-Packard (HP3000 line), and Sun Microsystems.IBM has made several models of midrange computers over these years: the System/3, System/34, System/32, System/36, System/38, and AS/400, which was recently rebranded to System i.Historically, midrange computers have been sold to small to medium-sized businesses as their main computer, and to larger enterprises for branch- or department-level operations.Since 1980s, when the client-server computing architecture became predominant, computers of the comparable class are instead universally known as servers to recognize that they "serve" end users at their "client" computers. Since the client-server model was developed in Unix-like operating systems, using this term vaguely implies support of standard—rather than proprietary—protocols and programming interfaces.
AS/400 is the base machine ie hardware - it runs an OS called Os/400. This has all the programming languages ie RPG, Cobol, C, C++ , Java etc.. It also comes with Apache web server built in and all the CGI api's that you need to web development.but the AS/400 also runs Unix, Linux.It can run virtual partitions, these can be OS/400 or any other os. You can also put in an intel card so it will run windows. Memory and disk cab be moved between the partitions dynamically.It is also very scalable ranging from 1 to 32 CPUs that can service thousands of users.The AS/400 is built round the power PC chip and uses common parts with the IBM unix server - they are basically the same hardware.It is IBM's biggest selling computer but unfortunaatly IBM does not tell the world about it. The figure here represents an IBM AS/400 server.
This figure shows the AS/400 server room in the IBM office.
AS/400 was the original name; it was replaced by iSeries when IBM began consolidating their servers under the eServer umbrella. There is a subset of iSeries known as i5 -- these have very specific hardware definitions.Note that an iSeries box is a physically different system from an AS/400 -- new processors, new all kinds of stuff.However, as the title of this topic indicates, _everybody_ except IBM still says "AS/400". That's something of an image problem because it helps perpetuate the "old, legacy, dinosaur, etc." image that you're going to run into over and over. You'll also run into programmers who couldn't care less about that image problem because they've discovered what AS/400s (iSeries) can do and have worked on enough alternative platforms to know the real story.
When IBM named the "iSeries", they chose the letter "i" to emphasize the point of "integration". E.g., the database is is "DB2 UDB for iSeries" and every program you write is aware of the database. If you reference a file in your program source, the compiler knows all about that file -- it knows what fields are in the records, what the data types the fields are, etc. Note that this is relevant to what's called "native I/O" and _not_ appropriate for SQL statements -- SQL has it's own way of determining data types, etc., and SQL is defined by independent standards, not by IBM.Likewise, security is integrated. Whether you make any explicit effort or not, every action you take, every object you create or access, everything is _always_ authorized by the security of the system. Some of this security is tied to the hardware and the hardware is also part of "integrated". This level of integration is why you never see security alerts that claim you can have a buffer overflow under OS/400 that lets you "run arbitrary code". (Although buffer overflows are just as possible, you can't get that overflow garbage actually to result in executeable code.)Likewise, and very important, work management is superbly integrated. This one is often forgotten because so few of us need to pay any attention to it; most of the defaults work for most environments. But if you start bringing someone in from Unix and start them learning what can be done with subsystems and routing and scheduling and all of its capabilities, they won't be able to demonstrate anything that comes close. Especially when it's so neatly integrated with security and communications and database and...Other things are integrated as well. With support for C/C++, Java, perl, COBOL, SQL, and plenty of other elements, there will be a career for a long time to come.
Where else one can find a platform that has you learning advanced server technologies, relational database, object-based programming, security, communications, Java, Unix APIs, etc., _AND_ can let you use COBOL too? From a solid foundation and understanding of OS/400, there's no place you can't go. (And few places you'll want to by then.)