JCC - The different file-open modes available on MVS datasets.

 fmode*vmode*vmodevmodeumodeumode*
  01201
Binary Records are read as streams, including any record padding. The same as text-mode, newline characters are used to delimit. In-Data-Stream lengths (2 bytes) before data stream starts. Block-mode stream doesn't use lengths at all (excl. blocksize.) Block-mode stream doesn't use lengths at all (excl. blocksize.) In-Data-Stream lengths (2 bytes) before data stream starts.
Text Records are trimmed and delimited by newline characters. Newline characters are used to delimit records into a block. Newline characters are used to delimit records into a block. Newline characters are used to delimit records into a block. Block-mode stream doesn't use lengths at all (excl. blocksize.) In-Data-Stream lengths (2 bytes) before data stream starts.
* Is the default used when extern vmode/umode have not been altered

Note: The DCB string allowed in fopen or _open may specify both a vmode= and umode= setting to cater for when either file types are opened.

These modes are for use when reading-only an old file or writing-only a new file, when using Read/Write mode all F/V/U blocked files become 'fixed block' (of blocksize length) binary type character streams, they request no trimming/translation and rounds up files sizes with a blocksize granuality even if only 1 byte is used in the block.

Read/Write supports binary and text mode but the only difference is the padding character used when closing the file (to fill out the incomplete current record and any remaining records in the block.)