Multipurpose computer boards can perform many related functions. There are several types of multipurpose computer boards. Examples include modem cards, fax cards, Ethernet cards, and serial/parallel adapters. An internal modem card is a device which is plugged in to an ISA or PCI slot on a computer and is used to transmit data from one computer to another across a telephone line. A modem card converts digital data to analog data from the sending end through the process of modulation. A modem card at the receiving end then performs demodulation of carrier signals to decode the transmitted information. A fax card is a PC circuit board that is plugged into a computer and enables files to be sent and received on a hard disk by fax. A fax card needs a modem to operate, and is usually built on the same card. An Ethernet card is a Printed Circuit Board (PCB) that is connected to a computer as an extension board and provides a standardized way of connecting computers together to create a network. Ethernet cards transfer data between computers over a line, wire, or cable. A serial/parallel adapter enables connection to parallel devices such as printers and to serial devices such as personal digital assistants (PDAs) through the USB port on the system. Other multipurpose computer boards are commonly available.