A physical file with multiple members all have the same record format definitions, but the actual data in one member is kept separate from the other members. Every physical file defaults to 1 member during creation.
Why do this? 1 example is receving a batch of data in a time stamped member. Each batch is kept separate & you can determine when you received it.
How to use the data? You need to use the OVRDBF command.
OVRDBF FILE(PROGFILE) TOFILE(LIBRARY/FILENAME) MBR(MEMBER)