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<div>The [[eServer]] iSeries runs [[OS/400]]. <br />
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==Overview of iSeries (OS/400) architecture==<br />
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From: http://www-1.ibm.com/servers/enable/site/porting/iseries/overview/overview.html<br />
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http://www-1.ibm.com/servers/enable/site/porting/iseries/overview/graphics/mult_os.gif<br />
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The recent iSeries servers, built on the [[POWER5]] hardware architecture, can equivalently run multiple simultaneous logical partitions of [[AIX]], [[Linux]], and the traditional iSeries operating system, [[OS/400]]. The most recent release of OS/400, Version 5 Release 4, is named [[i5/OS]].<br />
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While these other operating systems are peers to [[OS/400]] on iSeries servers, this page will focus on the traditional iSeries operating system. All of the features noted below represent [[i5/OS]], the latest generation of [[OS/400]].<br />
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===Overview of OS/400 architecture===<br />
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Several architectural features of [[OS/400]]'s architecture distinguish the system from other machines in the computing industry. These features include:<br />
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* Two-part primary operating system<br />
* Technology-independent machine interface ([[TIMI]])<br />
* Object-based system<br />
* Single-level storage<br />
* High degree of integration<br />
* Multiple application program models<br />
* Open Standards<br />
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===Two-part primary operating system, Technology-Independent Machine Interface===<br />
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http://www-1.ibm.com/servers/enable/site/porting/iseries/overview/graphics/timi.gif<br />
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There are two components to the operating system software on an iSeries server. This important distinction is unique in the industry in its completeness of implementation. The two components are:<br />
<B>System Licensed Internal Code</B> ([[SLIC]]) and <B>Operating System/400</B> ([[OS/400]]).<br />
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[[SLIC]] provides the [[TIMI]], process control, resource management, integrated [[SQL]] database, security enforcement, network communications, file systems, storage management, [[JVM]], and other primitives. [[SLIC]] is a hardened, high-performance layer of software at the lowest level, much like a Unix kernel, only far more functional.<br />
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[[OS/400]] provides higher-level functions based on these services to users and to applications. [[OS/400]] also provides a vast range of high-level language (such as [[C]]/C++, [[COBOL]], [[RPG]], [[FORTRAN]]) runtime functions. [[OS/400]] interacts with the client-server graphical user interface, [[iSeries Navigator]].<br />
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At a macro level, an entire logical partition running the traditional iSeries operating system, may be referred to as running [[OS/400]]. The name [[OS/400]] may refer to either the combination of both parts of the operating system or just the "top" portion.<br />
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===Object-based system===<br />
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http://www-1.ibm.com/servers/enable/site/porting/iseries/overview/graphics/obj.gif<br />
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[[OS/400]] keeps all information as objects. There are hundreds of object types, including the four examples above. This is different from the simple byte-string, file-based manipulation used by many systems. Object-based design enables a powerful, yet manageable level of system integrity, reliability, and authorization constraints.<br />
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All programs and operating system information, such as user profiles, database files, programs, printer queues, etc. have their associated object types stored with the information. In the [[OS/400]] architecture, the object type determines how the object's contained information can be used (which methods). For example, it is impossible to corrupt a program object by modifying its code sequence data as if it were a file. Because the system knows the object is a program, it will only allow valid program operations (run, backup). Thus, with no write method, iSeries program objects are, by design, highly virus-resistant. Other kinds of objects include directories and simple stream data files, such as video and audio files. These stream-file objects provide a with familiar open, read, and write operations.<br />
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===Single-Level Storage===<br />
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http://www-1.ibm.com/servers/enable/site/porting/iseries/overview/graphics/sls.gif<br />
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[[OS/400]] applications and the objects with which they interact all reside in a very large virtualized, single-level storage. That is, the entire system, including the objects most other systems distinguish as "on disk" or "in memory" are all in the single-level storage. Objects are designated as either permanent or temporary. Permanent objects exist across system [[IPL]]s (reboots). Temporary objects do not require such persistence. Essentially, the physical RAM on the server is a cache for this very large, single-level storage space. Storage management, a component of [[SLIC]], ensures that objects which need to persist when the system is off are maintained in persistent storage. This is either magnetic hard disk or flash memory as of this writing.<br />
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The benefit of providing a single, very very large address space, in which all objects on the system reside, is that applications need not tailor their memory usage to a specific machine configuration. In fact, [[OS/400]], due to the single-level storage, does not need to tailor such things as the sizes of disk cache vs paging space. This greatly facilitates the on-demand allocation of memory among logical partitions.<br />
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===Multiple Application Program Models===<br />
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http://www-1.ibm.com/servers/enable/site/porting/iseries/overview/graphics/apps.gif<br />
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Three models of running applications exist on [[OS/400]].<br />
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The traditional programming model for [[OS/400]] applications uses [[OS/400]]'s Integrated Language Environment ([[ILE]]). [[OS/400]] provides many programming interfaces to interact with system resources, and these are provided primarily as [[ILE]] interfaces. Applications in this model benefit from the [[TIMI]] for complete protection and benefit from future hardware changes. Support is provided for [[C]]/C++, [[COBOL]], [[RPG]], and [[CL]].<br />
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Applications from AIX can run inside an [[OS/400]] job, completely and seamlessly integrated into [[OS/400]]. This option is the [[OS/400]] Portable Application Solution Environment ([[OS/400]] [[PASE]]). Since the microprocessors are the same between traditional [[AIX]] and [[OS/400]] hardware, many components from [[AIX]] can run directly "on the silicon" in an iSeries server. [[PASE]] provides this very easy way to add, often unmodified, [[AIX]] applications to iSeries. [[PASE]] applications, just like [[AIX]] applications, interact with operating system functions through a syscall interface. However, since the applications are compiled to a specific processor instruction set, the investment protection of the [[TIMI]] is not afforded [[PASE]] applications. Support is provided for [[C]]/[[C++]], [[FORTRAN]], and [[COBOL]].<br />
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Support for [[Java]] applications is also built into [[OS/400]]. Java applications utilize a [[JVM]] and Java compiler that's built into the [[OS/400]] kernel ([[SLIC]]). The object-oriented nature of Java is an ideal fit for an object-based operating system like [[OS/400]]. If the Java application uses a Web application server, on [[OS/400]], it will best utilize [[WebSphere]] Application Server - Express, included with every iSeries server.<br />
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All three of these application program models normally coexist on [[OS/400]]. These all run on the same set of system resources such as network communications, user security, file systems, etc. It is common for code in one of these program models to call into code in another. The combination of these models affords great flexibility in bringing new applications to [[OS/400]].<br />
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==Summary==<br />
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The iSeries architecture is different from most other machines in the computing industry. It is a flexible architecture which is entirely focused on business computing. It runs business applications. It's largely self-managed, so customers can run their businesses, not their computers. It is based on the belief that a radically better system can be built. The unique architectural foundation of eServer iSeries will continue to allow leadership technological advancements well into the future.<br />
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==External links==<br />
*[http://www-1.ibm.com/servers/eserver/iseries IBM System i Home Page]<br />
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*[http://www.bosanova.net/thinclient/thinconfig.html Choosing the Right Thin Clients for your System i iSeries ]<br />
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[[Category:Hardware]]</div>Paulglen