There are two SCSI connections on the rear of the printer; they are not parallel connectors. The Personal LaserWriter SC communicates with a Mac OS compatible computer via SCSI and follows standard SCSI rules. If it is the only SCSI device connected, one port must be terminated, while the other port accepts the SCSI cable that goes to the computer. (The ports are the same; it does not matter which port gets the terminator and which gets the cable.) There is no support for printing to a DOS/Windows compatible computer.
Personal LaserWriter LS
The mini DIN-8 connection supports serial communication only with a Mac OS compatible computer via a serial Peripheral 8 cable. AppleTalk is not an option with the Personal LaserWriter LS. There is no support for communication with DOS/Windows compatible computers.
Personal LaserWriter NT
The mini DIN-8 connection supports AppleTalk communication with Mac OS compatible computers via LocalTalk connectors.
The The 25-pin socket will allow for RS-232c serial communication with a DOS compatible computer. This is not compatible for communication with a Mac OS compatible computer. The pushwheel switch determines what rate the serial communication will be and what protocols they will follow. This is not a SCSI ID number.
Personal LaserWriter 300
The mini DIN-8 connection supports serial communication only with a Mac OS compatible computer via a serial Peripheral 8 cable. AppleTalk is not an option with the Personal LaserWriter 300. There is no support for communication with DOS/Windows compatible computers.
Personal LaserWriter 320 and LaserWriter 4/600
The Personal LaserWriter 320 and LaserWriter 4/600 support only AppleTalk connections to the mini DIN-8 port with LocalTalk connectors. There is no support for printing to DOS/Windows compatible computers.