In a serial interface, the data is sent serially i.e. one bit after another. In other words, the bits form a queue and enter the printer one by one.
Serial ports are also known as Communication (COM) ports and are bi-directional. Bi-directional ports allow transfer of data in both directions i.e. receive and transfer data. Most standard serial ports have a maximum transfer rate of around 115 kbps (kilo bits per second). In other words, at any point in time, a serial port cannot receive or transfer more than 115kbps of data, although, newer ports support greater speeds.
Serial ports come in either 9 pins or 25 pins. Each pin has a specific purpose. For instance, pin numbers 2 and 3 are used to transfer and receive data respectively. Pin 4 is used to tell the computer that the printer is in ready state or is ready for a new print job.
