I/O Ports and Connectors B-1Appendix BI/O Ports and ConnectorsThis appendix provides specific information about theinput/output (I/O) ports and connectors on the back panelof the computerI/O Ports and ConnectorsThe I/O ports and connectors on the back panel of thecomputer are the gateways through which the computersystem communicates with external devices, such as akeyboard, mouse, printer, and monitor. Figure B-2 identi-fies the I/O ports and connectors for your system.Serial and Parallel PortsThe two built-in serial ports use 9-pin D-subminiatureconnectors on the back panel. These ports supportdevices such as external modems, printers, plotters, andmice that require serial data transmission (the transmis-sion of data one bit at a time over one line).Most software uses the term COM (for COMmunications)plus a number to designate a serial port (for example,COM1 or COM2). The default designations of your com-puter’s built-in serial ports are COM1 and COM2. COM1is the bottom connector; COM2 is on the top.The built-in parallel port uses a 25-pin D-subminiatureconnector on the computer’s back panel. This I/O portsends data in parallel format (where eight data bits, orone byte, are sent simultaneously over eight separatelines in a single cable). The parallel port is used primarilyfor printers.Most software uses the term LPT (for Line PrinTer) plus anumber to designate a parallel port (for example, LPT1).The default designation of the computer’s built-in paral-lel port is LPT1.Port designations are used, for example, in softwareinstallation procedures that include a step in which youidentify the port to which a printer is attached, thus tell-ing the software where to send its output. (An incorrectdesignation prevents the printer from printing or causesscrambled print.)
