Mainframes 360
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Friday, January 15, 2010

What on Earth is a Mainframe

Tutorial Description
What is a Mainframe Computer? Mainframe computers are used companies to process their business data. They offer Reliability, Availability and Serviceability(RAS). Learn about mainframe hardware, the peripheral devices you connect to a mainframe.
Operating system concepts, TSO and ISPF General Motors(GM) first started using operating systems. Multi-programmed and Time-sharing operating systems evolved. Learn about TSO as a command-processor, and how it achieves time sharing. ISPF is a menu-driven interface.
Mainframe Information Representation and Storage Learn about fields, records, files and datasets. Mainframe computers store data on Physical sequential datasets. Programs, Load-modules, User-procedures are stored in libraries called Partitioned Datasets.
Extents and z/OS file allocation  The mechanics of how z/OS allocates space to a new dataset. The location of a dataset is entered in the disk catalog. Know about B37, D37 and E37 space issues.
Get your hands wet on a Mainframe Get started, log on to a mainframe computer, allocate, edit and delete datasets.
ISPF Editor Commands The ISPF editor has built-in line commands and block commands. Learn how to edit a file in the ISPF Editor, move, copy, find and change data.
Structure of JCL A JOB tells which Program to run, what's the Input-File and what's the Output-File. Know, what’s the skeleton of a JCL like.
Basic Framework of JCL DD Statement comes in 3 flavours, to read data from a Dataset, Create a New dataset and store output, and Print information to the Log.
Multi-step Job Streams A multi-step job is made up of a chain of several inter-linked steps. Each Step runs a Program, takes input from preceding step, processes the Data, and produces output to be fed to the next Step.
Submitting a Job For This exercise, here are the artifacts
1. The Data Input File – referred to as 'AGY0157.DATA.INPUT'. Click
here. You'll need this, before you try to run the 3 step-Job.
2. The JESMSGLG Message Log Listing – After submitting the job, this is what the Message-Log in the SPOOL looks like. Click
3. The JESJCL Listing – This will contain the original source-JCL. Click
4. The JESYSMSG Listing – This will contain any allocation/deallocation messages. Click
here to see how it looks.
5. The Sorted Output SYSPRINT Listing – After running the 3-step toy-job, the Output Data is present in the SYSUT2 Listing of //STEP03. Click
here to see it.

To many people who are thrown to work at a mainframe computer on their first job, they feel lost. Mainframe people seem to speak a completely different language and that doesn't make life easy. What's more, the books and manuals are incredibly hard to comprehend.

"What on earth is a Mainframe?" is an absolute beginner's guide to mainframe computers. We'll introduce you to the hardware and peripherals. We'll talk about the operating system, the software installed on a mainframe. We'll also talk about the different people who work on a mainframe. In a nutshell, we'll de-mystify the mainframe.

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