In addition to normal "linked" and "random" files, FMS also has non-structured files. Non-structured files are used to catalog tapes and private non-standard disk packs. They are also used by the Automatic Storage Manager (ASM a.k.a. SMS) for "migrated" and "logical" files.
Normal and non-structured files are distinguished by a bit in the "fixed" area of the type 2 (file description) FMS catalog block. For non-structured files, the variable area of the type 2 block has fields which distinguish the various types of non-structured files, as well as fields specific to each type (tape density etc). B/MANIF/NSTRUCT defines manifests to locate an interpret these fields.
B/MANIF/FMS must also be included by any program using NSTRUCT.
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