IBM i Series, Handbook

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iSeries Architecture: Fundamental Strength of the iSeries
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iSeries Handbook
On a customary machine, many of these software modules are provided by third parties. A
customer has to assure that someone integrates all these modules and performs the tests
necessary to verify that they all function together. When one of the software components has
a new release, a customer again needs to ensure that component is replaced, plus any other
software modules on which it depends. The modules need to be at compatible release levels.
Should a software malfunction occur, how do you establish precisely which modules are
causing it? Can you be certain that multiple third-party software vendors agree with your
diagnosis when you blame their software?
OS/400 does not have any of these problems. To achieve the functionality that is standard in
OS/400, a customer would need to integrate typically between 10 and 25 different modules of
software. OS/400 is installed with all these capabilities as standard. When software is
updated, a new release of OS/400 is made available. OS/400 customers do not have to install
individual system software components, nor do they have to check that releases can co-exist.
Object-based
An object is a container. Everything the system uses—user and system data structures—is
packaged in one of these containers. The objects are encapsulated, which means that you
cannot see inside. Inseparable from an object is the list of valid ways in which that object can
be used.
There are two important consequences of an object-based design. The first is that a system
built around an object model supports machine independence. This means that technology
changes can be made in the environment without affecting application programs. The second
consequence is that an object-based design delivers a high level of system integrity and
security.
All objects are structured with a common object header and a functional portion dependent
on object type. Therefore, on the iSeries servers, instructions work on only what they are
supposed to work. Data cannot be treated as executable code (so that the processor tries, for
example, to execute someone's shoe size). Executable code cannot be treated as data (by
having something written into the middle of it).
Certain instructions apply to all objects, while other instructions work only on specific types of
objects. It is not possible to misuse an object, unlike the situation that exists for non-iSeries
systems without an object-based approach.
Java
Java is a key application development environment for the iSeries server. AS/400 Developer
Kit for Java supports Sun's Java 2. The Java Virtual Machine, which resides below the iSeries
Layer, enables fast interpretation and execution of Java code on the iSeries servers. In
addition, a type of static compiler is available called a
class transformer
, to generate RISC