The Application System/400 (AS/400)

The Application System/400 (AS/400), renamed to iSeries in 2000, further renamed to System i5 in 2006, is an IBM minicomputer for general business and departmental use, introduced in 1988 and still in production under the names iSeries and i5. The AS/400 is an object-based system with an integrated DB2 database that was designed to implement E. F. Codd's relational database model, which is based on Codd's 12 rules, in the operating system and hardware. All software necessary to run this computer is included and integrated. More than 2,500 business software applications were available when the first AS/400 was delivered in 1988. The AS/400 is well suited to a broad range of business, non-profit, and government applications, including back office, manufacturing, retail wholesale transportation, data base management, being an ISP. It is not a suitable platform for scientific number crunching or consumer applications.

The AS/400 was the result of the combination of the System/38 database machine (announced by IBM in October 1978 and delivered in August 1979) and the System/36. The first AS/400 systems (known by the development code names Silverlake and Olympic) were delivered in 1988, and the product line has been refreshed continually since then. IBM renamed the AS/400 to iSeries in 2000, as part of its e-Server branding initiative. The product line was further extended in 2004 with the introduction of the i5 servers, the first to utilize the IBM POWER5 processor. The AS/400 was the first general-purpose computer system to attain a C2 security rating from the NSA, and in 1995 was extended to employ a 64-bit processor and operating system. The architecture of the system allows for future implementation of 128-bit processors when they become available. Existing programs will utilize the new hardware without modification.


Features include an extremely fast DBMS, a menu-driven interface, multi-user support, terminals (IBM 5250) and printers, security, communications, client-server and web-based applications and an extensive library-based operating system, OS/400.


A big selling point is that applications can run without modification on any model in the product line, from small, single-processor machines up to those with 64 multi-core CPUs. For traditional business programming languages such as RPG, COBOL, C and SQL, it has support for external files, display files and object-based programming, which allows for increased programming productivity. It also supports Unix-like file directories, industry-leading support for Java, client-server technologies and a native Apache web server, for "modern" and GUI-style applications. IBM claims superior Total cost of ownership due to high system availability, which averages 99.98% uptime, and lower costs of administration and maintenance, when compared to Unix, Linux and Microsoft-based implementations.


The machine was originally based on a custom IBM CISC CPU which used a CPU architecture known as Internal MicroProgrammed Interface (IMPI) and an instruction set similar to the IBM 370. It was later migrated to a PowerPC-based RISC CPU family eventually known as RS64. The latest models are based on the POWER5 (announced 4 May 2004) processor.[1]


Here Debian is running natively on an iSeries Logical Partition.The machine survives because its instruction set (called TIMI for "Technology Independent Machine Interface" by IBM) allows the operating system and application programs to take advantage of advances in hardware and software without recompilation. This means that a program written and compiled on a S/38 can be run as a native 64-bit program. The HAL allows a system that costs $9000 to run exactly the same operating system and software as a $2 million system. The system can concurrently run multiple operating systems (i5/OS (OS/400), Linux, AIX) natively, and runs Windows Server and Linux on one or more single-CPU blade servers or externally-attached mutiple-CPU servers when installed. The 64-bit design provides for the seamless addressing of up to 16 exabytes (16 million terabytes) of storage.


The AS/400 enforces the use of the TIMI virtual instruction set for all user-mode programs; it is not possible for such programs to utilize the instruction set of the underlying CPU, thus ensuring hardware independence. This is conceptually somewhat similar to the virtual-machine architecture of programming environments such as SmallTalk, Java and .NET. The key difference is that it is embedded so deeply into the AS/400's design as to make all applications and even the bulk of its operating systems binary-compatible across different processor families. Note that, unlike other virtual-machine architectures in which the virtual instructions are interpreted at run-time, TIMI instructions are never interpreted. They constitute an intermediate compile-time step and are translated into the processor's instruction set as the final compilation step. The TIMI instructions are stored within the final program object, in addition to the executable machine instructions. This is how a program compiled on one processor family (e.g. CISC) can be moved to a new processor (e.g. PowerPC) without re-compilation. The program is saved from the old machine and restored onto the new machine, whereupon the OS discards the old machine instructions and re-translates the TIMI instructions into machine instructions for the new processor.


The AS/400's instruction set defines all pointers as 128-bit to allow seamless transition from older to new processor generations.


Another feature that was recently introduced to the AS/400, LPAR, came from IBM's mainframe line of computers. LPAR (Logical PARtitioning) facilitates running multiple instances of operating systems simultaneously on one AS/400 unit. A system setup with LPAR can even run different operating systems on different partitions while ensuring that one OS cannot run over the memory or resources of another. Each LPAR is given a portion of system resources (memory, hard disk space, and CPU time) via a system of weights that determines where unused resources are allocated at any given time. The OSes supported (and commonly used) under the LPAR scheme are OS/400, AIX and Linux. (Note: Currently Microsoft operating systems do not support Power-based processors.)


AS/400s are also capable of supporting mutiple instances of Linux, Microsoft Windows 2000 and Windows Server 2003, with either single-processor internal blade servers (IXS) or externally-linked mutiple-processor servers (IXA).


Even though AIX can now be natively run in an LPAR partition, the original implemenation was to allow AIX programs to be ported to the PASE environment. AIX programs ARE binary compatible with OS/400 when using OS/400's PASE (Portable Applications System Environment). PASE is essentially "an operating system within an operating system", supporting the most recent stable version of AIX. Binaries need to be re-compiled on the AIX system, with 16-bit (quadword) pointer alignment enabled. Once the program is compiled with this option, the executable can be FTP-ed to the AS/400, and executed under the PASE Korn Shell.


Additionally, tasks such as handling record locks and queuing updates are managed automatically by the system, making high-speed, multiuser applications easy to create and maintain, and extremely reliable.


Programming languages available for this machine include RPG, assembly language, C, C++, Java, COBOL, SQL, BASIC, PHP, PL/I, and REXX. Several CASE tools are available: Synon, AS/SET, Magic,and Lansa.

Commands in the Control Language (CL) are promptable and most provide cursor-sensitive help to make entering parameters easier. A command name consists of a three-letter verb and a subject part, also referred to as a noun. Some command names provide a "modifier" as well. This is intended to make it easy to understand CL code. Examples:

CRTUSRPRF - Create (verb) user (modifier) profile (noun) DLTLIB - Delete (verb) library (noun) CPYF - Copy file WRKACTJOB - Work with Active Jobs The AS/400 was designed as the successor of the IBM System/38 and the IBM System/36. The programmers who worked on OS/400, the operating system of the AS/400, did not have a UNIX background. Dr. Frank Soltis, the head architect, says that this is the main difference between this and any other operating system.


Despite the lack of a "UNIXy" background, the AS/400 has, over the years, picked up the programming/runtime model found on UNIX, Linux, and PC systems. Traditional AS/400 programming is a "one-stop shop", where a programmer writes computer code, compiles the code, and then executes the code. There is no link step that is found in other environments.


However, in 1995, that changed. IBM re-christened the one-stop shop programming style "OPM" (for Original Programming Model) and introduced a new language paradigm called "ILE" (for Integrated Language Environment). ILE had significant enhancements over OPM, including the ability to create modules (similar to .obj or .lib files), and then bind (link) the modules together into a single executable. The executable could be created as a program or a service program (service programs are similar to .lib or .dll files).


The real power of the ILE environment is in the "integrated" aspect, however. Modules in ILE-compliant languages (RPG, COBOL, C, C++, and CL) could be created and bound together. For the first time, AS/400 programmers could exploit the strengths of multiple ILE-compliant languages in a single program. Also, with the introduction of service programs, standard routines could be externalized more easily, and modularity increased. To ensure proper migration to the ILE environment, OPM RPG and COBOL programs could be migrated to ILE easily.


Interoperation with the Java language is also supported, though not as tightly as with the ILE languages. The iSeries Java implementation is distinguished by the depth of its embedment in the operating system.


iSeries servers also support common client-server-based technologies such as ODBC and JDBC for accessing its database from client-based software, created with languages such as Java, Microsoft Visual Studio .NET and other languages.