ANDREW COLLETT Concepts in Mainframe Computing

Contents Brief History and General Information Pros/Cons of Mainframes Terminology Concepts used in the mainframe world Mainframe process example

History & General Information IBM Mainframe Definition ..”a large computer, in particular one to which other computers can be connected so they can share facilities the mainframe provides.... The term usually refers to hardware only, namely, main storage, execution circuitry and peripheral units” MIPS  Million instructions per second  IBM’s way of rating their mainframes

History & General Information First IBM Mainframe  April 7, System/360 $5.5 Million to purchase or ~$3,000-$100,000/month rental  to MIPS IBM zEnterprise System – 2010  5.2Ghz per core with up to 96 cores on a single machine  3 TB of main memory  78,426 MIPS  industry standard today – more variations  ~$33 Million to buy/install and ~$256,000 / year to maintain

Pros of Mainframes Extremely fast Can handle a huge workload 24/7 Consolidates the entire system together Easy to manipulate data quickly Great for transaction processing Ton of support through IBM

Cons of Mainframes Very expensive up front cost Expensive to maintain – MIPS and hardware maintenance Have to pay based on how many MIPS are actually being executed - if renting Complex system – high learning curve Not good for number crunching or doing complex calculations Some systems can be old and outdated

Why are mainframes still around? Nothing can match the speed of data processing that mainframes deliver Nothing can match the volume and reliability of data processed Has a lot of money, time, and energy invested into it  Esp. IBM – TON of support  Older systems cost too much to replace Old systems need maintenance  Trillions of lines of code that is used everyday  Banks, financial institutions, big businesses, etc

Terminology EBCDIC  EBCDIC is a standard similar in concept to, but not compatible with, ASCII COBOL  A business-oriented programming language z/OS  A 64-bit operating system that allows for virtualization of resources – what mainframes newer than 2000 run on REXX  A scripting language that is similar in concept to Perl and Python

Terminology CICS  A transaction server for online and batch processing JCL  A scripting language for executing batch programs Batch  Schedule based jobs that runs every night with an interconnected series of scripts DB2  the IBM relational database management system, also available on other platforms

EBCDIC Extended Binary Coded Decimal Interchange Code Devised in by IBM to co-release with its System/360 mainframe 8-bit character encoding  Developed separately from the 7-bit ASCII encoding scheme

EBCDIC

COBOL COmmon Business-Oriented Language Used in mainframes because they were built and structured around each other Business oriented language so it is English like Easy to read in files and manipulate records while applying business logic

REXX Restructured Extended Executor Developed by IBM Designed as a macro or scripting-like language so each mainframe system can do unique things Allow for developers to make ‘App-like’ programs on the mainframe.  Ex. Typing a shortcut on the command line  Small program to cleanup some files

REXX

z/OS 64-bit operating system that runs on mainframes designed by IBM  Needs to be at least a “zSeries” or newer mainframe Record-oriented data access methods Supports Java, C++, and C# (built in compiler) Comes with all the necessary tools to work on a mainframe – CICS, DB2, JCL, REXX, etc.

z/OS Meant for continuous, high-volume operation with high security and stability Newest version – IBM Rational Development for System Z  z/OS on Windows  No ‘Green Screen’  Nice GUI – based on Eclipse client  Has subversion type software built in  Has ‘Content Assist’ – just like Intellisence

IBM Rational Development for System Z

CICS Customer Information Control System Is a Teleprocessing monitor server  a control program that monitors the transfer of data between multiple local and remote terminals to ensure that the transaction processes completely or, if an error occurs, to take appropriate actions Transaction server that runs mostly on IBM mainframe systems under z/OS Middleware designed to support high-volume online transaction processing

CICS CICS transaction is a unit of processing initiated by a single request that may affect one or more objects Interacts with resources such as files, database connections, terminals, or to invoke functions such as web services Manages the entire transaction – if transaction fails all recoverable changes can be backed out 90% of Fortune 500 companies run on CICS  Bank teller systems, ATMs, insurance agencies, record keeping, etc.

JCL Job Control Language Instruct the system on how/when to start a batch job Job, steps, and procedures JCL has scripting-like tools that can be used depending on the system  Sort files before running, copy data to a different location, etc

JCL Example

JCL Once the JCL is made without syntax errors it can be ‘submitted’ to the mainframe The mainframe will run the job just as the card says The example shown will run the program named ‘COBPROG’ with the given input and output files in addition to the ‘MYINPUT’ input

Batch Processing Jobs that run directly on the mainframe that do a lot of transaction processing need to be scheduled No manual intervention – controlled automatically ProgA needs to run before ProgB because ProgB has input that is created by ProgA Most companies have their own software on their mainframe that will do job scheduling  Zeke for z/OS Event Scheduling

Zeke

DB2 for z/OS Database server product developed by IBM – DBMS  manages incoming data, organizes it, and provides ways for the data to be modified or extracted by users or other programs Supports SQL and XQuery Primary way of getting and storing usable data for programs that need it Integrated into Rational Development for System Z where it can generate usable error free SQL

DB2

DB2 Error Processing 3 Types of return codes 0 – successful execution Positive number – successful execution with one or more warnings Negative number – unsuccessful with an error Easy to handle errors

Conclusion All of these concepts work together Huge sandbox with many tools Mainframe advancements will continue to be made through these tools along with new mainframe hardware These are the things that a developer must know in order to be a successful programmer on a mainframe

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C#

PC ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Rational Development for System Z (z/OS)

PC Rational Development for System Z (z/OS) COBOL Program P1 JCL to run the program Uses DB2 Output - Report

PC Rational Development for System Z (z/OS) COBOL Program P2 JCL to run the program Input file is Prog1’s Output report

PC ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Rational Development for System Z (z/OS) Batch Scheduler (Zeke) Set Prog2 to run directly AFTER Prog1 finishes

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing COBOL Program P1 JCL to run the program Uses DB2 Output - Report

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing COBOL Program P1 JCL to run the program Uses DB2 Output - Report Gets needed data Via DB2

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing COBOL Program P1 JCL to run the program Uses DB2 Output - Report Output

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing Output

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing COBOL Program P2 JCL to run the program Input file is Prog1’s Output report Output

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing COBOL Program P2 JCL to run the program Input file is Prog1’s Output report Input

ZEnterprise Mainframe z/OS CICS DB2 JCL REXX COBOL BATCH EBCDIC JAVA C++ C# Nightly Batch Processing P2 finished

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