string OpenVMS usage:char_string type: character string access: read only mechanism: by descriptor Command line. The string argument is the address of a descriptor of a TPU command. fileio OpenVMS usage:vector_longword_unsigned type: bound procedure value access: read only mechanism: by descriptor File I/O routine. The fileio argument is the address of a descriptor of a file I/O routine. call_user OpenVMS usage:vector_longword_unsigned type: bound procedure value access: read only mechanism: by descriptor Call-user routine. The call_user argument is the address of a descriptor of a call-user routine.