VTAM
The part of z/OS that connects 3270 terminal sessions and SNA networks to applications such as TSO and CICS.
Also written SNA, APPLID, Communications Server, Virtual Telecommunications Access Method
VTAM, the Virtual Telecommunications Access Method, is the part of z/OS that handles SNA, IBM's original networking system. Today it is part of z/OS Communications Server, together with TCP/IP.
Its most visible job is 3270 sessions. Each application that users connect to, such as TSO, a CICS region or IMS, is known to VTAM by a name called its APPLID. The first screen you see after connecting, where you type something like LOGON APPLID(CICSPROD) or choose from a menu, is usually a VTAM screen.
Most 3270 connections now arrive over TCP/IP, using TN3270, but they are still handed to VTAM, which connects them to the right application.
You may see the abbreviation USS in VTAM documentation. There it means unformatted system services, the VTAM logon screen, which has nothing to do with Unix System Services. Network specialists look after VTAM. For other staff, it matters mostly when you cannot reach an application, because the message on the screen often comes from VTAM.
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Right here, at ZedBank. You take a junior job at a simulated bank and learn each part of the work by doing it, with Zed beside you. There's nothing to install.
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- 3270 terminalThe classic mainframe display device, and the protocol still used today to talk to z/OS over a network.
- LogonSigning on to a mainframe system with a user ID and password to start an interactive session.
- TSOTime Sharing Option: the interactive login environment on z/OS, where you get a command prompt and a session of your own.
- CICSThe transaction manager that runs online mainframe applications, and the software behind a great many screens bank staff use.
- CICS regionOne running copy of CICS, with its own programs, files and users. A site typically runs several.
- Green screenThe text-only, keyboard-driven interface most mainframe work happens through, named after the green phosphor of early terminals.