Everyone knows what 3270 means, right? Sure, within the mainframe community, 3270 is a common term, but what about those non-mainframers out there? 3270 is used to describe quite of lot of things related to accessing the mainframe: 3270 terminals, 3270 applications, 3270 protocols, and TN3270 emulators. In this post, we will try to provide some relevant information that will help everyone better understand 3270 and the related terms.
3270 Mainframe Terminal: History
The original IBM 3270 mainframe terminal was released in 1971 to replace its predecessor, the IBM 2260. Consisting of a screen and a keyboard, the 3270 was a non-programmable terminal and was meant to be used in conjunction with a centralized mainframe. This was happening over the limited bandwidth networks at that time. Because of it was a non-programmable workstation, the 3270 was often called a “dumb” workstation.
Companies adopted 3270 terminals in large numbers. Indeed, in the ‘70s and ‘80s, most large companies throughout the world were using an IBM mainframe computer, often running CICS or some other competing software application. Typically, the organization would then utilize 3270 terminals to connect with the mainframe.
Early on, an IBM 3270 mainframe terminal consisted of only a few components: a big CRT (Cathode Ray Tube) monitor, a keyboard, and a coaxial cable which connected the terminal to the mainframe by way of a control unit. Amazingly, with only 16MB of memory, an IBM 3033 mainframe from the 1970s could support up to 17,500 3270 terminals under a single CICS application!
Each of the 3270 terminals were communicating with the mainframe using the “3270 data stream” language. The goal of the language was to maximize the number of terminals that could be used from a single mainframe without frequent interruptions.
Nowadays, the 3270 mainframe terminals have disappeared from companies and have been replaced by PCs for the most part. However, the 3270 data stream language is still being used, interpreted by various kinds of 3270 emulators.
3270 Mainframe Applications
Also known as green screen applications, 3270 mainframe applications are accessible through 3270 terminals or TN3270 emulators. The most well-known of the building-block applications are:
Conversational Monitor System (CMS) is a simple and interactive, single-user operating system. CMS runs as a “guest” operating system inside of a private virtual machine. The user typically logs onto VM first, then enters the command ‘i cms.’ The VM control program and CMS together create a multi-user time-sharing operating system.
Time Sharing Option (TMO) is an interactive time-sharing environment for IBM mainframe operating systems (i.e., z/OS). This allows many users to use the system concurrently without interfering with each other. This is achieved mainly through TSO’s single login capability (unique ID and password for each user). Once logged in, users can use ISPF (Interactive System Productivity Facility) to interact with the mainframe.
Customer Information Control System (CICS) is a family of mixed-language application servers that allow millions of transactions to be processed everyday all around the world. The CICS Transaction Server (CICS/TS) is the most important part of the CICS family and it provides online transaction management and connectivity for applications on IBM mainframes.
You’ll find that most financial institutions and insurance companies use CICS. Using CICS/TS on z/OS is still arguably the most efficient and cost-effective way to process millions of transactions daily.
CICS is called a mixed-language application server because it supports many different coding languages (from Java to COBOL). Moreover, not only does CICS support large volumes of transactions very efficiently, but it also acts as middleware, standing as a mediator between other programs, the UI, and the data.
Information Management System (IMS) is a database and transaction management system (just like CICS). It holds two components: the IMS Database Management System (IMS DB) and the IMS Transaction Management System (IMS TM). IMS DB, which is more widely used than IMS TM, is also known as a hierarchical database management software. This way the integrity of the data is ensured while the storage and retrieval process are optimized.
TN3270 Emulators
Nowadays, you’ll mostly find 3270 terminals inside museums or in the possession of diehard IBM fans. But thanks to 3270 emulators, 3270 applications are still being used today. The most classic 3270 emulator is called the TN3270 emulator, or Telnet 3270 emulation software, which takes its name from the Telnet protocol it uses to communicate with the mainframe. There are TN3270 emulators for Mac, for Windows, and for Linux.
TN3270 Protocol
The Telnet 3270 protocol (or TN3270) was based on the original Telnet protocol which was defined in RFC 854. The purpose of the Telnet Protocol is to provide a standard method of interfacing terminal devices and terminal-oriented processes to each other. TN3270 was built on this underlying protocol to allow the terminal emulator to communicate over TCP/IP networks.
At first, Telnet was an open, non-secure protocol. However, in 1995, specifications for securing it appeared (SSL, then TLS for instance). It is therefore possible and soon became a requirement to secure TN3270 communications, but many companies haven’t implemented it. Since it is sometimes difficult to configure encrypted data streams, implementing a VPN is often the chosen method. Many older versions of emulators do not support SSL, requiring the IT team to perform complicated maneuvers to support it.
Wrap-Up
TN3270 emulators are also referred to as heavy-client emulators as they require the installation of a client software on each end-user device. However, this entails many admin obligations such as constantly and manually keeping it up to date on each end-user device.
While the 3270 terminal has completely disappeared from company offices, the 3270 family still survives to this day with its reliable applications and emulators. Moreover, the 3270 family is not frozen in time. Many innovations are being made for the 3270 family to this day.
For instance, thin-client TN3270 emulators like Virtel Web Access can function solely with a modern web browser. They even have functionalities such as on-the-fly transformation of traditional “green screens” into modern pages. These emulators bring new quality of life functionalities and bridge the gap between legacy applications and the web.
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