| _FORK_fcb | The Fork Control Block |
| _FORK_msg_hdr | All messages queued by the FORK routines must be prefaced by this controlling structure |
| _FORK_msg_sys | A predefined message consisting of a FORK_msg_hdr and a single 32-bit location to hold the contents |
| _FPA_fcb | Layouts the control structure for managing the list of free packets. This structure is private to the FPA utility |
| _FPA_pcb | Layouts the control structure used by each packet on the free list This structure is private to the FPA utility |
| _GPS_irep | An integer binary representation of the GPS data |
| _GPS_latitude | Holds a latitude reading |
| _GPS_longitude | Holds a longitude reading |
| _GPS_pm_mbf | Symbolic layout of a GPS Position Message in Motorola Binary Format |
| _IVTE_dir | Directory structure definition |
| _IVTE_hdr | Header structure definition |
| _IVTE_tlr | Trailer structure definition |
| _LL_list | Defines the control structure needed to describe the head of a linked list |
| _LL_node | Defines the control structure needed to maintain a node on a linked list |
| _LLI_list | The list head control structure |
| LLI_node | The node control structure |
| RNG_rcb | The Ring Control Block structure |
