This decision depends on how you use your VTAM terminals. For example, a terminal that is logged on all the time can be autoinstalled, but you might choose to define it individually.
An autoinstall logon is slower than a logon to a terminal individually defined to CICS, so if you switch continually between applications and have to log on to CICS frequently, you may require individual definitions for some terminals.
You should also consider your use of automatic transaction initiation (ATI), terminal list tables (TLTs), and the intercommunication methods in use in your installation. See Deciding which terminals to autoinstall.
CICS supplies some TERMINAL and TYPETERM definitions; these are listed in TYPETERM definitions in group DFHTYPE and Model TERMINAL definitions in group DFHTERM. You can use these definitions if they are suitable; if not, create your own using CEDA or DFHCSDUP.
Define an autoinstall model for each different kind of terminal to be autoinstalled. Try to keep the number of definitions to a minimum, so that the autoinstall control program can be as simple as possible.
When you create your definitions, consider whether you want to use the QUERY structured field (see TYPETERM definition attributes). It can help the autoinstall control program to choose which model on which to base a definition, and so speed up the autoinstall process.
For every region using autoinstall, redefine DFHZCQ to be RESIDENT(YES). (DFHZCQ is in the CICS-supplied group DFHSPI). See the CICS Performance Guide for guidance on why you should consider making programs resident.
Autoinstall and VTAM explains the relationship between CICS autoinstall and VTAM. For programming information, including a list of VTAM LOGMODE table entries, see the CICS Customization Guide.
The terminal autoinstall control program is invoked by CICS every time there is a valid request for a TCT entry to be autoinstalled, and every time an autoinstalled TCT entry is deleted.
For programming information about the autoinstall control program, see the CICS Customization Guide. The autoinstall control program for VTAM terminals provides a summary of what the program is about.
Before beginning your program, look at the CICS-supplied autoinstall control program DFHZATDX in group DFHSPI to see if it is suitable for what you want to do with autoinstall.
You can enable autoinstall for terminals either by using the system initialization table (SIT) or by using the EXEC CICS or CEMT INQUIRE∨SET SYSTEM command.
Five system initialization parameters relate to terminal autoinstall:
The purpose of the limit is to protect the system from uncontrolled consumption of operating system storage by the autoinstall process, as a result of some other abnormal event. Normally, in the process of autoinstall, the principal consumer of CICS storage is the autoinstall task (CATA) itself. The amount of CICS storage consumed by the autoinstall process during normal operation can therefore be controlled by creating an appropriate TRANCLASS definition to limit the number of autoinstall tasks that can exist concurrently.
For information on how to specify these system initialization parameters, see CICS System Definition Guide.
Three options relate to terminal autoinstall on the INQUIRE∨SET AUTOINSTALL command:
You can prevent more terminals from logging on through autoinstall by setting this value to 0. This allows autoinstalled entries for terminals currently logged on to be deleted by the autoinstall program when they log off.