COM Ports COM1 and COM3 use IRQ 4. COM2 and COM4 use IRQ 3. Most PCs only have two external COM ports. Parallel Ports Parallel ports are used for printers, scanners, and sometimes drives. It sends and receives 8 bit of data at one time.
External ports send data in an asynchronous fashion.
Video Video is a HDA connector. It is a 15 pin female with 3 rows of pins. 50 feet is the maximum length a serial cable should be. SCSI SCSI cables communicate between a SCSI port and a SCSI device, or between two SCSI devices. Hard drives, tape drives, optical drives, scanners, and CD-ROM drives can all use the SCSI interface.