MFS control blocks

There are four types of MFS control blocks that you specify to format input and output for the application program and the terminal or remote program.

The four types are:

Message Output Descriptors (MODs): Define the layout of messages MFS receives from the application program.
Device Output Formats (DOFs): Describe how MFS formats messages for each of the devices the program communicates with.
Device Input Formats (DIFs): Describe the formats of messages MFS receives from each of the devices the program communicates with.
Message Input Descriptors (MIDs): Describe how MFS further formats messages so that the application program can process them.

Throughout this information, the term message descriptors refers to both MIDs and MODs. The term device formats refers to both DIFs and DOFs.

Each MOD, DOF, DIF and MID deals with a specific message. There must be a MOD and DOF for each unique message a program sends, and a DIF and MID for each unique message a program receives.