System Control Blocks

Contents Directory Entry
(MVT Only)
The contents supervision feature of the
supervisor determines the location of
requested programs, fetches the program to
main storage if necessary, and schedules
the execution of these programs for the
request,ing tasks .As a byproduct of these
functions, records are kept of all programs
in main storage.
One of these records is the contents
directory entry (CDE), which describes the
requested module. Each area of storage
occupied by a job step has a contents
directory recording each load module
requested by the step. Entries in the
contents directory (CDEs) contain the names
of load modules and pointers to their entry
points. The CDE is initialized with
descriptive information from the input
parameters of the request. When the module
is located, its attributes are further
recorded in the CDE.
If the caller has specified an alias
entry point within the called module, two
contents directory entries will be created
for that module. One, the major CDE,
contains the main entry point name: the
other, the minor CDE, contains the alias
entry point name.
CDEs are maintained either within a 'job
pack area control queue (JPACQ), which is
pointed to by the TCBJPQ field of the MVT
task control block, or within a link pack
area control queue (LPACQ), which contains
CDEs describing modules normally resident
in the link pack area.
Figure 2 illustrates the format of the
CDE. Descriptions of the fields follow the
illustration.
contents Directory Entry 11