INTRODUCTION TO AS/400Mid-range Machines
IBM AS/400 belongs to the category of minicomputers or the so called mid-range machines. These are generally medium sized computers and are between microcomputers and mainframe computers in terms of processing speed, storage capacity and the number of users that can be supported at once. There may be various reasons to opt for a mid-range machine over microcomputer or a mainframe. Microcomputers may not provide speed and storage capacity to the required extent. The no. of users supported is also less. Mainframes, inspite of having all the above facilities are very costly and require specialized personnel for their set-up and maintenance and also occupy a lot of space with special environmental conditions.
Evolution of AS/400
The AS/400 is the latest mid-range machine introduced by IBM with the latest advancements and software incorporates which make it an efficient, easy-to-use and an unbeatable low cost business server. However, its history dates back to July, 1969, when IBM had introduces the S/3 (System 3) series. This was when IBM made a debut in smaller systems. It offered use of punch cards that were three times in size to todays punch cards but could contain 120 percent of data.The next member of S/3x family was introduced in January, 1975, known as S/32. It allowed the user to interact with the system through a keyboard and a monitor that could display only 240 characters (6 rows and 40 columns). It supported 32 KB of main memory and had a 13 MB hard disk.
In April 1977, the S/34 was into the market which provided multiple workstation support (including printers) and could handle upto 8 local users at a time. It had a 256 KB main memory and 14 GB hard disk. The S/38 was the next machine to be announced in October 1978, which was different from its S/3x predecessors. The architecture of this machine was optimised for application development productivity, which supported 256 local workstations, 32 MB of main memory and 14 GB of secondary storage. On the other hand, development on S/34 architecture continued which led to the advent of S/36 in May, 1983 which supported upto 72 local workstations, and had 7 MB of main memory and 1.4 GB fixed disk. Finally, in June 1988 the first of the AS/400 machines was introduced where AS stands for Application System. It was an expansion of S/38 architecture but also provided application program compatibility with S/36.
There are three categories of software on the AS/400: Application Software Operating System Software Licensed Internal Code (LIC) AS/400 USER
Operating System S/W
Application Software This is the top layer of software that performs user tasks and acts as the primary interface between the user and the AS/400. This includes system-supplied functions like PDM (Program Development Manager), purchased software like a case tool, and other specialized user-developed systems. This software can also execute or call the OS programs. Operating System Software This is the middle layer of software which performs most of the system housekeeping tasks and manages the system resources. It includes common OS functions like copying and deleting files, which can be invoked by application programs through CL (Control Language) commands. LIC Licensed Internal Code - the deepest layer of software, is an IBM-supplied set of programs that provide the database, security, communications, and other essential functions. Users never interact directly with the LIC, and it cannot be tampered by programmers or system operators. Another advantage of LIC is that no time need spent on installation of software for the system to run. LIC also provides the hardware
interface, thereby any changes to the hardware invite corresponding changes to the LIC. However, the application programs need not undergo any changes, thereby reducing maintenance costs.
Salient Features of AS/400
The following are few of the salient features of the AS/400 machines IBM offers several choices of AS/400 models so that user can balance between requirement and financial budget. AS/400 supports 64-bit memory addressing thereby has a large working storage memory. Therefore largest AS/400 model has more than 40GB RAM that can be accessed by OS/400. It has a 64-bit processor which provides enhanced arithmetic capabilities. The machine comes with an in-built operating system OS/400 which is also object based and layered which makes upgradation very easy. The user can upgrade his AS/400 model to higher configuration conveniently. Single storage, i.e., the auxiliary storage is treated as an extension of the working storage. Thus the OS/400 enjoys very large virtual memory. It has got an integrated RDBMS DB2/400 and provides a high level of security as the control to DB2/400 is controlled by OS/400. Every AS/400 has DB2/400 as pre-installed. It is compatible with other IBM ranges like PCs to mainframes. Offers Double Byte Character Set. This allows users to generate characters more than EBCDICs usual set. Thus storage and display of many human language characters is possible. AS/400 is used to represent more than 50 languages in the world. Communication: AS/400 has Client Server environment. There are basically three types of Client-server environments. a. Distributed Display. Where input-output interfaces are sent to clients and actual data storage and processing is done on server. b. Distributed Data: where apart from input-output interfaces even a set of data is also sent to client so that there will be less transaction between client and the server and client may improve performance of application as it may not depend of server frequently for the next set of data to be displayed. c. Distributed Processing: In which some part of application can be executed on client reducing the load on server and making effective utilization of hardware and software resources. The program running of client may interact with a program running on server. This has been possible since the introduction of micro computers in the industry. AS/400 offers all the three options to user. The OS/400 uses TCP/IP is telnet protocol to enable communication between client and server. IBM has also provided there own protocol System Networking Architecture (SNA) as another choice. The software that implements this protocol and enables the communication is called as Client Access software. Following are some Client Access software used on AS/400 to create the environment of AS/400 on client (many time PC). 1. IBM Personal Communication 2. RENEX 3. MOCHA SOFT 4. RUMBA/400
Software: AS/400 runs on OS/400 Operating System. The latest version of OS/400 is V5R3. Features: 1. It is most secured operating system of industry. 2. Offers character based but user friendly interface. Several thousand help and command prompt screens. 3. LPAR : Logical Partition offers multiple environments on same server. User can run Windows NT, LINUX 4. Has multi-threaded environment with multiple subsystems to manage concurrent jobs. These jobs can well be scheduled also. 5. No data loss in case of communication failure or system failure. 6. Various logs and Audit trails makes system C2 level secured.
Languages: a. b. c. d. e.
Control Language/400. An OS command language. RPG/400 used to write commercial application. High Level Language. (HLL) COBOL/400. Common Business Oriented Language (HLL) PASCAL/400 C/400 C++/400 Java/400 Object Oriented languages.
Development tools: (Third party) SYNON, LANSA , ASSET Packages: Office Vision/400, JD Edward, MOVEX , BPCS IBM has provided some utilities along with system that help developer while building application. They are called as Application Development Tool Set (ADTS).UtilitiesThe following utilities are provided by the IBM AS/400.
SEU Source Entry Utility used to code the programs, structure of database files etc. DFU Data File Utility used to make data entry directly in to the database files. SDA Screen Design Aid used to create User Interface, i.e., the screens used in interactive programs. RLU Report Layout Utility used to design the layouts of the reports that are going to be used in the programs. PDM Program Development Manager an in-built utility for the user to navigate through various source physical files etc.
Storage Hierarchy: OS/400 is Object based operating system. Every thing that is stored on AS/400 as a separate entity (collection of information) known by OS/400 is an Object on AS/400. Unlike Object Oriented Programming system the object on AS/400 is a permanent entity having its own attribute. In fact different type of objects on AS/400 have different attributes and depending on these attributes only OS/400 treats them. The program type of object can not be modified. That means when you compile any program source the existing object by same name is deleted and re-created but OS/400 does never allow program object just to be modified. So there is no possibility of virus getting inserted in program like EXE file under Windows. Database (file) type of object can be modified for add/update/delete of records. Some objects used for device configuration purpose can not be moved from one place (directory) to another.
There are around 100 type of objects on AS/400. The logical partition on AS/400 is called as Auxiliary Storage Pool (ASP). The ASP is like C drive D drive etc on Personal Computers except that the ASPs on AS/400 are numbered. Within ASP are what are called as Libraries. Library on AS/400 storage is also one type of (*LIB) object that logically hold other objects. For understanding lets compare them to the concept of directory of personal computers. So objects logically belong to any specific library. There are different type of Libraries. 1. System Library: These are pre-defined libraries on the system. They contain objects of OS/400, Device configurations, Subsystems, job queues , user profiles , message queues etc, They also contain language compilers, function libraries, DB2/400 RDBMS system etc. 2. User Library: These are libraries created by user. There is one system library called as QSYS. All libraries can be created inside this QSYS library. There can not be library inside a library except that QSYS. For storing program sources and Data Description Specification (DDS) IBM has provided one file type of object called as Source Physical File. Multiple sources can be stored within one source physical file. One group of lines of one source is called as source member within a source physical file. A source physical file belongs to any library.
Sub-systems A subsystem is a single module of OS that is dedicated to perform a specific task on the OS. There can be many subsystems active on a single machine and they can be handled or controlled independently. The number of subsystems that can be active at one time is limited only by the resources available on the system. Some of the IBM supplied subsystems are QBASE and QCTL (the default controlling subsystem). As per the need either of the above can be used. AS/400 also allows users to copy and change the existing subsystems or create new ones to support the special data processing needs. Jobs Any single task uniquely identified by the system is a job. Each of such jobs could be controlled individually and therefore, the work load can be managed at the individual job level. There are two kinds of jobs, viz., interactive and batch. An interactive job starts when a user signs on the workstation. Such a job comprises of the work performed based on the inputs received from the user during his tenure on the workstation. On the other hand, a batch job is placed in a queue (job queue) to be started by a subsystem. Such jobs are specified with a priority and they are carried out based on their respective priorities. Queues Objects that are of special importance to operators are queues. They are holding areas for messages, printed reports, batch jobs, and other work that is waiting to be received, released to the CPU, or accessed by a specific user. There are three categories of queues, viz., message queues, job queues and output queues. A job queue holds the jobs that have been submitted for batch processing and they get processed based on their priority. The job Queues belong to subsystem. There can be predefined number of jobs active at a time within a job queue. Jobs more than such number have a status as *jobq. That means these are in a queue waiting for resources available. Communication between the programs, between jobs, between users, between users and programs and between users and the system occurs through messages. A message queues holds the message that is to be
sent to a specified user or a program it is placed in the message queue associated with the user or the program. The OS/400 provides message queues for: - Workstations on the system - System history log - Users responsible for system operation - Users enrolled on the system Whenever a request is sent to print the data etc., the data retrieved from the database is placed is formatted by a print device file. Such formatted print files are placed on an output queue until a writer is ready to send the information to a printer. Such requests also have the flexibility to be processed based on the priority assigned to them.
Latest versions of this machine called the e-Series/i-Series also supports JAVA on As/400.
Introduction to AS/400 Historical PreviewIntroduced in 1988 Originated as the Successor of S/38
AS/400 ArchitectureSophisticated design and ease-of-use come together in the AS/400
Layered ArchitectureAS/400 Architecture
Conventional System Architecture
Applications and HLL
CL SQL DDS
Communication , Database, Security, other Add-on softwares
OS/400 (Integrated System Services) MI VMC (Operating system supervisor) IMPI HMC (Microcode) Solid State Hardware
Operating System SupervisorConventional Machine Instruction set
Microcode Solid State Hardware
It is a software layer Interface masquerading as a machine with a very powerful instruction set. Consists of 260 Instruction
Vertical MicrocodeIt is not a actually a microcode, The Code in the VMC layer is IMPI, or Machine code. Formats Similar to S/370 machine Instructions, The following are the few instructions Register-to-register (RR) Register-immediate (RI) Register-and-storage(RS) Storage-to-Storage(SS) And branch instruction IMPI instructions also use base-register addressing similar to the S/370.
Opcodes 0 8
R2 12 15
S/370 RR format
Opcodes 0 8
R2/E 12 15
AS/400 RR format
Horizontal Microcode and HardwareIt is a true Microcode. 42-Bit Micro Instruction (also ca...