Types of commands

Three types of commands operate at three levels:

TSO commands, CLISTs, and REXX EXECs
You invoke high-level commands through the MVS/TSO operating system. These include TSO commands, CLISTs, REXX EXECs, and the commands assigned to the PA1 and PA2 keys.
DM component commands
You call middle-level commands through the DM component of ISPF.
PDF component primary and line commands
You call low-level commands through the PDF component of ISPF.