Summary of VSAM Data Set Types

Table 1 summarizes what each data set format offers.

Table 1. Comparison of ESDS, KSDS, fixed-length RRDS, variable-length RRDS, and linear data sets
ESDS	KSDS	Fixed-Length RRDS	Variable-Length RRDS	Linear Data Sets
Records are in order as they are entered	Records are in collating sequence by key field	Records are in relative record number order	Records are in relative record number order	No processing at record level
Direct access by RBA	Direct access by key or by RBA	Direct access by relative record number	Direct access by relative record number	Access with data-in-virtual (DIV)
Alternate indexes permitted¹	Alternate indexes permitted	No alternate indexes permitted	No alternate indexes permitted	No alternate indexes permitted
A record's RBA cannot change	A record's RBA can change	A record's relative record number cannot change	A record's relative record number cannot change	No processing at record level
Space at the end of the data set is used for adding records	Free space is used for inserting and lengthening records	Empty slots in the data set are used for adding records	Free space is used for inserting and lengthening records	No processing at record level
A record cannot be deleted, but you can reuse its space for a record of the same length¹	Space given up by a deleted or shortened record becomes free space	A slot given up by a deleted record can be reused	Space given up by a deleted or shortened record becomes free space	No processing at record level
Spanned records permitted	Spanned records permitted	No spanned records	No spanned records	No spanned records
Extended format permitted¹	Extended format or compression permitted	Extended format permitted	Extended format permitted	Extended format permitted
Note: Not supported for HFS data sets.