File Control Table (File architecture)

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The File Control Table contains the file parameter settings, data set or file definition names of all data sets in the file, the status of the file, and other control information.

The FCT is 8 pages.

The first page of the FCT is the File Parameter List (FPL) page, which contains:

  • The File Parameter List holding the current parameter settings for the file
  • The Logical Page Map (LPM) which shows the distribution of the pages within the file
  • The data sets list (DSL) comprising the name and number of pages in each data set
  • The shared DASD enqueue list, which:
    • Controls access to the file by multiple jobs, potentially running on different processors that share the DASD device upon which the file data sets reside
    • Contains the enqueue level of each of those jobs. The ENQCTL command enables you to display the enqueue list.
  • The current file broadcast message (if any), displayed when the file is opened.
  • The segment page array table. This contains a 3-byte pointer to the existence bit map for each segment of the file. From V7.5 onwards, if the FILEORG x'200' bit has been set during file creation to indicate that the file is a large file, then this table is moved to the second page of the FCT.

The remaining seven pages ( or six pages if the FILEORG x'200' bit is set ) of the FCT are empty. They were used in very early versions of Model 204, but now they are "Reserved for Future Use."