DISK{(*EXT | record-length)}

The DISK keyword is a device-type keyword. It is used in a free-form file definition to indicate that the file device is DISK. It must be the first keyword.

The parameter is optional. It defaults to *EXT.
*EXT
Specify *EXT to indicate that the file is externally described. This is the default.
record-length
Specify a record-length to indicate that the file is program described. The record length must be between 1 and 32766. It can be a literal or a named constant. If it is a named constant, the constant must be defined prior to the file definition statement.