4.4. Extended addressability (EA)
Extended addressability (EA) was introduced in DFSMS/MVS 1.3, for KSDS data sets. Since DFSMS/MVS 1.4, EA is supported in record level sharing (RLS). With DFSMS/MVS 1.5, support for extended addressability is extended to all other VSAM record organizations.
With EA, the 4G architectural limit for data set size imposed by using the 4-byte field for the relative byte address (RBA) was eliminated.
It is important to state that extended addressability and extended format are not the same concept. Extended format is a way of storing data in a 3390/3380 logical volume. Extended addressability is the ability of allowing larger VSAM data sets. However, extended format is a pre-prerequisite for extended addressability. ...