VMS Help EXCHANGE, COPY, Qualifiers, /TRANSFER_MODE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /TRANSFER_MODE=option

    Specifies the I/O method to be used in a transfer. This qualifier
    is useful for all volume formats.

    Option   Function

    AUTO     Select BLOCK transfer for efficiency if possible
    BLOCK    Transfer block by block without looking at records
    RECORD   Transfer record by record

    The default is the AUTOMATIC transfer mode. In AUTOMATIC mode,
    EXCHANGE attempts to use a BLOCK transfer whenever possible.
    BLOCK transfers are possible between RT-11 volumes or between
    RT-11 and DOS-11 volumes, since the internal file structures are
    identical. AUTOMATIC does not use the BLOCK transfer if either
    file specification contains a /RECORD_FORMAT qualifier.

    A BLOCK transfer moves data between devices. Since no
    interpretation is done on the data, BLOCK transfers are more
    efficient than RECORD transfers. The block sizes on both devices
    must be identical. Both input and output must be in BLOCK format.
    Specifying BLOCK on one parameter implies BLOCK for the other
    file or device specification.

    A BLOCK transfer produces an exact copy of the file. If the
    output device is Files-11, the file will be a sequential
    file with fixed-length 512-byte records. This feature is used
    primarily to avoid any interpretation of the data during the
    transfer. If the Files-11 file is a sequential file with 512-byte
    fixed-length records, there is no difference between a /TRANSFER_
    MODE=BLOCK transfer and a /RECORD=FIXED=512 transfer.

    A RECORD transfer moves the data record by record. A RECORD
    transfer requires more time than a BLOCK transfer, but it must
    be used if the input and output record structures differ.

    When the /LOG qualifier is used in a COPY command, EXCHANGE
    displays the size of the file that was transferred. If BLOCK
    mode was used, the message gives the file size as the number of
    blocks transferred. If RECORD mode was used, the message displays
    the number of records.