cases the line number is synthesized from data that appears at the start of an input line or the line number can be prepended to an output line. File or device names Input/output is done directly by referencing a file or device by its name (FDname) or indirectly by referencing a logical I/O unit (SCARDS or INPUT, SPRINT or PRINT, SPUNCH or OBJECT, GUSER, SERCOM, 0 to 99). FDnames are assigned to logical I/O units using keywords in the command language or by default. FDnames can be a simple file name such as MYFILE, a simple device name prefixed with a greater than sign such as >T901, or a pseudo-device name such as *PRINT*. All FDnames are converted to uppercase before they are used, so like MTS commands, FDnames are case independent. I/O modifiers, line number ranges, and explicit concatenation can be used to create complex FDnames from simple FDnames. For example: FILE1@-TRIM (I/O modifier that retains trailing blanks) FILE2(1,10) (line number range that reads lines from 1 to 10 inclusive) FILE3+*SOURCE* (explicit concatenation) FILE4(1,10)@-TRIM+*TAPE*@-TRIM (all of the above in a single complex FDname) Pseudo device names Pseudo device names (PDNs) begin and end with an asterisk (e.g., *name*). Common pseudo devices include: *SOURCE* standard input (normally either a terminal or for batch jobs, the input queue); *SINK* standard output (normally a terminal or for batch jobs, a printer); *MSOURCE* master source, not re-assignable, usually a terminal or a card reader; *MSINK* master sink, not re-assignable, usually a terminal or a printer; *BATCH* spooled input to a new batch job; *PRINT* spooled output to a printer, same as *MSINK* for batch jobs; *PUNCH* spooled output to a card punch (until card punches were retired); and *DUMMY* all data written is discarded and all reads return an End-of-File (much like /dev/null for UNIX); and *AFD* the active file or device as established using the $GET command. The $SOURCE and $SINK commands may be used to reassign the FDnames assigned to *SOURCE* and *SINK*. The $MOUNT command assigns pseudo device names (e.g. *T22*, *NET*) to devices such as magnetic and paper tapes and network connections (including server connections). The $CREATE command can be used to create pseudo device names for use with BITNET import and export, for spooled print jobs, and for dummy devices. I/O modifiers I/O modifiers, possibly negated, may be associated with an FDname to modify default behaviors. An I/O