Parallel is the opposite of series, which as applied to data means that instead of bytes being sent bit by bit, one after the other (usually down a single wire), parallel data sends many bits simultaneously down several wires. Whole bytes or more can be transmitted at once. On PC’s parallel ports are often used to connect tape drives, CD-ROMs, extra hard disks, and most printers. These ports can transmit faster than serial ports, but usually cannot reliably send data more than 20 feet. SCSI, in all its various forms, is also a type of parallel interface that has its own set of standards and protocols for very high speed data transfer.