Ports

In addition to the I/O ports mentioned in the last section which are really addresses, there are physical connections on the back of the computer that are also called ports, and various devices connect to the computer through cables attached to these ports. One of these connections is called the Serial Port because data goes over a single signal line as a series of bits, one right after the other.

Serial port connectors have either 9 or 25 pins, with the male connector on the back of the computer and a female connector on the cable. The 9-pin version is more common, and is often used to connect a mouse if there is not a separate mouse connection.Another connection is called the Parallel Port because its cable has 8 parallel signal lines to transmit 8 bits at a time. The computer has a 25-pin female connector on the back, so it won’t be confused with the 25-pin male serial connector. The parallel port is most often used to connect a printer.



Computers sold in the last few years will probably also have a connection called USB, for Universal Serial Bus. It is a bus because several devices can be connected on the same cable, but it’s also a port because data goes into and out of the computer cabinet through its connector. There is USB1 and USB2. USB2 is newer and much faster.