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Overview of IBM Mainframe access:

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The most common "traditional" way to get interactive access to an IBM mainframe system (System/370 and later) was to use an IBM CRT display terminal in the "3270" family. These terminals were commonly attached to the mainframe by way of a dedicated communications network or directly on-site to a display controller. The most popular basic model was the 3278. It and its successors offered a wide variety of options, such as color support, the number of characters displayable (from 80 x 25  up to  80 x 43 or 132 x 27), a light pen for "point and click", special purpose keyboards, and graphics support. There was also a companion 3287 printer.

Software support for these terminals was provided by the host mainframe. At the basic level, there was the Virtual Telecommunications Access Method (VTAM, now known as SNA Services, under Communications Server). The Time-Sharing Option (TSO)  used VTAM and provided a command-line interface and line-by-line interactivity. (TSO was originally designed in 1971 for pre-CRT tele-printer terminals, much as RT-11, CP/M, PC/MS-DOS, and UNIX were.) The Interactive System Productivity Facility (ISPF) was added in the late 1970's to run as a part of TSO and provide character-mode full-screen menus and full-screen text editing. Other software sub-systems, such as IMS DC (Information Management System--Data Communications) and CICS (Customer Information Control System) could also use VTAM to access terminals and provide more advanced forms of interactive processing, such as on-line transaction processing (OLTP).


A) Nowadays, PC's stand in for 3270 terminals when accessing "classic" mainframe applications and environments. There are several ways that this can be accomplished.

    1) The PC runs 3270 terminal "emulation" software.

        a) The PC is equipped with additional hardware which allows it to be connected directly to a legacy network or controller, exactly as if it were a 3270-family terminal. (Dial-in connections directly to the host via modems is another possibility, but not commonly used anymore.) In this case, the emulation software usually runs as a separate stand-alone PC application.

        b) The PC uses the Internet to communicate with the mainframe host. A special version of Telnet, the Internet's remote-login facility, is the most common protocol. The Internet Engineering Task Force (IETF) defines this special version of the Telnet protocol, called Telnet 3270, or TN3270 for short (RFC's 1041, 1576, 1646, 1647, 2355, 2561, 2562, 3049). TN3270E is an enhanced version of TN3270. Any method used to connect the PC to the Internet may thus be used to access mainframe hosts/servers also connected to the Internet. There are several way that the terminal emulation software can be implemented in this case.

            i) The 3270 terminal emulation software can be a separate PC application, as in 1a), above.

            ii) The 3270 terminal emulation software can be a "plug-in" to a standard web browser. This has the advantage that the emulation software can be automatically installed into the browser under the control of the server. However, if the Internet connection is made using a 56Kbps modem, for example, the software download process can take a half-hour or more. On the other hand, the download process should only occur on the first connection to the host, if there has been an upgrade to the emulation software, or if the PC user has done something that would cause the emulation plug-in to be uninstalled.


IBM has a TN3270 browser plug-in called Host-On-Demand (HOD). IBM's stand-alone access software is called IBM Personal Communications (PCOM), and can access iSeries (midrange, formerly AS/400, etc.) and zSeries (mainframe, formerly System/390, etc.) systems. A combo package is called IBM Host Access Client Package, and can be ordered on-line. (You don't want the one restricted to the iSeries.)

There are many third-party sources for 3270 emulation software. Prices range from $25 to $250 or more. Trial downloads and shareware are common. At this point, I do not have a strong recommendation of one over the others. I would suggest looking for the "IND$FILE" feature, since this will facilitate transferring source code and data files between the PC and the mainframe. 3287 printer emulation may also be a useful feature.

The IBM Academic Initiative (formerly Scholars) zSeries Program @ Marist has been directing its users to Tom Brennan Software for a free TN3270 emulator download, until problems with HOD are resolved.

MochaSoft provides Telnet 3270 terminal emulation (TN3270) for many client platforms
(It does not currently seem to support the IND$FILE protocol for uploading and downloading files between the client and host.)

If free and open software is your bag, you might explore the combination of x3270 (a Linux-based terminal emulator), and Cygwin (a .dll file and related software, which create a "substantial" Linux API within the Microsoft Windows environment) or Cygwin/X (Cygwin + XFree86 X Window v11 (a.k.a. X11R6)). If you are a Linux guru, check this out and let us know the details for setup and usage.

You can find a more extensive list of TN3270 client software at:


    2) The mainframe host can run front-end software that provides a web "wrapper" around VTAM or one or more interactive sub-systems, such as CICS (CICS Transaction Gateway or CICS Web Support). In these cases, any standard web browser can access the mainframe without additional terminal emulation plug-ins. This is a more recently implemented technique, and is not yet very common.


B) In recent years, IBM has incorporated AIX, its proprietary version of UNIX, into the OS/390 operating system and its successor, z/OS. This sub-system is known as Unix System Services (USS). It is also offering a separate Linux option, which can be run in multiple partitions under the VM/390 or z/VM operating systems. In as much as both USS and Linux are versions of Unix, they communicate using plain old Telnet, not TN3270, as well as plain old File Transfer Protocol (FTP) and other well known Unix and Internet protocols. USS has implemented many features to facilitate compatibility with classic applications. Nevertheless, it should be noted that applications implemented in and for a classic mainframe environment may need significant modification and/or recompilation to run in either UNIX-based mainframe environment.

Most browser software comes already equipped to handle plain old Telnet and FTP. Microsoft also continues to provide stand-alone TELNET and FTP utilities, which can be run from the command line (PC/MS-DOS prompt). There are a number of enhanced freeware packages for these protocols (PuTTY, for example). There are also many shareware and commercial third-party providers of Telnet and related communications software. Some of the commercial packages also include TN3270, and TN5250, a terminal emulation protocol used by IBM AS/400 and iSeries systems.


C) IBM's WebSphere® is a more comprehensive software development environment and Internet/Web strategy that includes:

1) Foundation & Tools: Java, and XML-based software and services that allow applications to be implemented on all four eServer® platforms: xSeries (Intel x86/Pentium/etc.), pSeries (PowerPC, formerly RS/6000, etc.), iSeries, and zSeries; as well as cross-platform Linux, Intel-based PC's and Java Virtual Machine platforms (While holding on to its xSeries server line, IBM recently sold its Intel-based workstation, aka "PC," business to Lenovo, a Chinese company--still pretty good product from the looks of it.);

a) Open Services Infrastructure: WebSphere Application Server,

i) WebSphere Application Server - Express

ii) WebSphere Application Server

iii) WebSphere Business Integration Server Foundation (formerly WebSphere Application Server Enterprise): V5.1 for multiplatforms & V5.1 for z/OS

iv) WebSphere Application Server for z/OS

v) IBM WebSphere Studio (see b) below)

vi) WebSphere Application Server Technology for Developers, V6

b) Application Development: WebSphere Studio;

i) WebSphere Studio Homepage Builder: Web

ii) IBM WebSphere Studio Site Developer: Web

(a) Eclipse technology

iii) WebSphere Studio Application Developer: Web services, portals, & J2EE applications

iv) WebSphere Studio Application Developer Integration Edition: for building composite applications that deploy to IBM WebSphere Business Integration Server Foundation

v) WebSphere Studio Enterprise Developer: J2EE, XML, Web services, Enterprise COBOL, Enterprise PL/I, RAD deployable to WebSphere, CICS, IMS, & Batch (z/OS?)

vi) WebSphere Studio Device Developer: J2ME - PDAs, cellular telephones, & pervasive devices

vii) WebSphere Studio Asset Analyzer

viii) iSeries Development Family

(a) WebSphere Development Studio for iSeries

(1) includes (b) following

(2) Server components: ILE RPG (IV), ILE COBOL, ILE C/C++, Application Development ToolSet (ADTS; includes Source Entry Utility (SEU), Screen Design Aid (SDA), Report Layout Utility (RLU), Data File Utility (DFU), Character Generator Utility (CGU), Advanced Printer Functions (APF), Programming Development Manager (PDM), Host Access Programs for CODE/400 and VisualAge for RPG, Interactive Source Debugger (ISDB), File Compare and Merge Utility (FCMU), plus enhancements)

(b) WebSphere Development Studio Client for iSeries (i.e., PC-based tools)

(1) Remote System Explorer

(2) iSeries Projects

(3) Web Tools for iSeries

(4) Java Tools for iSeries

(5) IBM WebFacing Tool

(6) Classic tools (CODE/400 & VisualAge for RPG)

(7) standard client comes with WebSphere Studio Site Developer (see above)

(8) Advanced Edition comes with WebSphere Studio Application Developer (see above), which includes everything from Site Developer plus many additional features, such as J2EE Enterprise Java Bean development tools

(9) client also coordinates with WebSphere Studio Application Developer Integration Edition & WebSphere Studio Enterprise Developer (see above)

ix) Toolkits for IBM WebSphere Studio

c) Enterprise Transformation: specialized software and services that facilitate Web access to legacy applications on the iSeries and zSeries.

i) WebSphere Studio (see above)--including Enterprise Developer, Asset Analyzer, & WebSphere Development Studio for iSeries

ii) WebSphere Host Integration.

(a) WebSphere Host Access Transformation Services (HATS): Converts host screens (3270 for zSeries, 5250 for iSeries) to "web-like" GUIs on the fly

(b) The Host Access Client Package, mentioned above, is also included here.

(1) WebSphere Host on Demand

iii) CICS Transaction Gateway

d) WebSphere and zSeries

i) Model and Discover

(a) CICS Interdependency Analyzer
Runtime analysis of CICS® business and technical processes for understanding and workload management

(b)Rational Rose® XDE Modeler
Produce language-independent Unified Modeling Language (UML) models of software architecture, business needs, reusable assets and management-level communication.

(c) WebSphere Business Integration Modeler
Tools to design, test, and communicate complex business processes

(d) WebSphere Studio Asset Analyzer
Quickly analyze and identify existing assets for reuse, and impact analysis

ii) Integrate and Develop

(a) CICS Business Event Publisher for MQSeries®
Integrate mainframe applications and data with the rest of your enterprise without change

(b) CICS VSAM Transparency
The migration of data from VSAM to DB2® without modification to the CICS or batch VSAM application programs

(c) IBM Enterprise COBOL and PL/I for z/OS V3.3
COBOL EJB Support and XML enhancements

(d) WebSphere Host Access Transformation Server
Easily extend existing applications to the widest possible audience

(e) CICS tools

(f) WebSphere Studio Enterprise Developer (WSED)
Comprehensive end-to-end development environment for traditional and Web developers

iii) Test, Deploy and Manage

(a) Application Monitor for z/OS (AM)
Bottleneck isolation of online and batch application performance with ability to drill down to source

(b) CICS Interdependency Analyzer
Understanding of active application inventory for efficient maintenance and upgrade

(c) CICS Online Transmission Time Optimizer
3270 data streams optimization for increased system performance

(d) CICS Performance Analyzer
Comprehensive off-line performance reporting and analysis for tuning and capacity planning

(e) CICS VSAM Copy
On demand consistent copies of VSAM data with no interruption to the on-line user

(f) CICS VSAM Recovery
Automated recovery of lost VSAM data for improved integrity to your CICS solution

(g) CICS Performance Monitor
Real-time performance management, monitoring and troubleshooting for increased availability

(h) Debug Tool and Debug Tool Utilities and Advanced Functions (DT/DTU)
Source code debugging, and application coverage to improve development productivity

(i) Fault Analyzer for z/OS (FA)
Rapid access to pinpoint cause of failed application

(j) File Manager for z/OS (FM)
Data management tool supporting key file structures: VSAM, DB2, and IMS

(k) IBM Rational Functional Tester Extension for Terminal-based Applications:
Extends IBM Rational Functional Tester for Java and Web to test 3270 (zSeries) and 5250 (iSeries) terminal-based applications

(l) IBM Session Manager
Secure, reliable, and easy access to multiple z/OS® and OS/390® applications from a single terminal for higher end-user productivity

(m) IMS and DB2 Tools
Designed to enhance the performance of IBM IMS and DB2 Universal Database for z/OS and for Linux, UNIX®, and Windows®.

(n) WebSphere Studio Application Monitor (WSAM)
Determine location of bottlenecks and resolve application problems in both WebSphere and CICS

(o) WebSphere Studio Workload Simulator (WSWS)
Understand and benchmark response times against the number of expected users, prior to deployment

(p) Workload Simulator for z/OS
Understand and benchmark response times against the number of expected users, prior to deployment

iv) Run

(a) CICS Transaction Server
Transaction processing solution that provides powerful and flexible support for e-business applications

(b) IMS Transaction Server
IMS, IBM's premier transactional and hierarchical database management system for critical on-line operational and e-business applications and data

(c) Rational Software
Rational® software helps organizations create business value by improving their software development capability

(d) WebSphere Application Server
High-performance and extremely scalable transaction engine for dynamic e-business applications

2) Business Portals

a) Interactive User Experience: WebSphere Portal

b) Access On Demand

i) WebSphere Everyplace

ii) WebSphere Voice

c) Selling and Channel Management: WebSphere Commerce

3) Business Integration

a) Business Integration

b) Product Information Management

4) Related Products

a) Transaction Servers & Tools

b) WebSphere - Express

D) Other software-development-based access

1) VisualAge

a) VisualAge COBOL

b) VisualAge C++

c) VisualAge Enterprise Suite

d) VisualAge for Java (trade up to WebSphere Studio Site Developer V5.0)

e) VisualAge Generator

f) VisualAge Pacbase

g) VisualAge PL/I for OS/390

h) VisualAge PL/I for Windows (NT)

i) VisualAge Smalltalk

j) VisualAge TPF

Click here for a squib on how to retrieve IBM mainframe system output via e-mail. (I have actually gotten this to work after considerable fumbling around).

Here is link to how we have installed IBM Personal Communications for Windows v5.7 at Metro.


Alan R. Reinarz, Instructor