A hardware computer port is a physical interface between a computer and other computers or devices. A software computer port is a virtual data connection between computer programs possibly through a computer network.
The Hardware ports come in different sizes such as round, rectangular, square, trapezoidal etc. They can be serial ports or parallel ports. The difference between them is in sending and receiving bits. Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-) Parallel ports send multiple bits at the same time over several sets of wires. A parallel port is also referred to as the printer port since that is usually the device that plugs into it. Many other peripherals have been created to use the parallel port including external CD-ROM drives and ZIP drives. While plugging these devices into the parallel port makes them extremely easy to set up.
A COM Port stands for communications port and is also referred to as a serial port. Most intial computers have at least four COM ports internally which modems or other internal peripherals se. every computer has at least one and usually two external COM ports for physically attaching external peripheral devices, such as external modems, scanners, and digital cameras.
USB stands for universal serial Bus and is a common component on new computers. The port looks like a flat slot and there are usually two of them together. More than 120 devices in new computer peripherals (digital cameras, scanners, speakers) come with USB adapters that allow the user to plug the unit into the computer and use it immediately without having to install expansion cards inside the computer and make manual adjustments to the computer settings. These are also called Plug-and-play ports. They are such that once they are in used; the connected devices start handshaking automatically. USB Ports are typical examples of the plug-and-play. For Example, in a USB port, you can plug a USB Drive, USB Mouse, USB Keyboard etc. and the devices are detected automatically.