The Information Center Facility names service maintains a system names directory and users' private names directories. These names directories help users locate other users, and assist them in transmitting messages through the system.

The names service keeps directory information in ISPF tables. There are two types of table entries: single user entries, and group entries that apply to more than one user. The size and type of an entry can vary, along with the total number of directory entries. As a result, the total size of the personal and master directories can vary. The maximum size for a single user entry is 715 bytes, with the average size being 350-400 bytes. Group entries consist of 300 bytes per group, plus an additional 15 bytes per group member. A copy of the user's personal directory table and a copy of the concatenated personal and master directory tables reside in private area virtual storage. In addition to the storage for individual and group entries, each copy requires 1K bytes of additional virtual storage.

When users update the master directory, the names service requires an additional table to hold the updates. Each update requires a maximum of 800 bytes, with the average size being 400-450 bytes. A single table holds the updates for all users and empties as the administrator processes the updates. The total size of the additional table depends on the rate at which users update the master directory and the rate at which the administrator processes those updates. A copy of the table resides in private area virtual storage, requiring 1K bytes of virtual storage, in addition to the storage for individual and group entries.

The names table and all ISPF tables are loaded above 16 MB in virtual storage.