On computers, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various peripherals, and directly between computers.
A male D-subminiature connector used for a serial port on an IBM PC compatible computer along with the serial port symbol
An IBM PC serial card with a 25-pin connector (obsolete 8-bit ISA card)
A PCI Express ×1 card with one serial port
A four-port serial (RS-232) PCI Express ×1 expansion card with an octopus cable that breaks the card's DC-37 connector into four standard DE-9 connectors
In computing, a parallel port is a type of interface found on early computers for connecting peripherals. The name refers to the way the data is sent; parallel ports send multiple bits of data at once, as opposed to serial communication, in which bits are sent one at a time. To do this, parallel ports require multiple data lines in their cables and port connectors and tend to be larger than contemporary serial ports, which only require one data line.
A DB-25 connector often used for a parallel printer port on IBM PC compatible computers, with the printer icon.
Micro ribbon 36-pin female, such as on printers and on some computers, particularly industrial equipment and early (pre-1980s) personal computers.
Mini-Centronics 36-pin male connector (top) with Micro ribbon 36-pin male Centronics connector (bottom)
The Apple II Parallel Printer Port connected to the printer via a folded ribbon cable; one end connected to the connector at the top of the card, and the other end had a 36-pin Centronics connector.