In computer hardware, a port serves as an interface between the computer and other computers or peripheral devices. In computer terms, a port generally refers to the part of a computing device available for connection to peripherals such as input and output devices. Computer ports have many uses, to connect a monitor, webcam, speakers, or other peripheral devices. On the physical layer, a computer port is a specialized outlet on a piece of equipment to which a plug or cable connects. Electronically, the several conductors where the port and cable contacts connect, provide a method to transfer signals between devices. Bent pins are easier to replace on a cable than on a connector attached to a computer, so it was common to use connectors for the fixed side of an interface. Computer ports in common use cover a wide variety of shapes such as round (PS/2, etc.), rectangular (FireWire, etc.), square (Telephone plug), trapezoidal (D-Sub — the old printer port was a DB-25), etc. There is some standardization to physical properties and function. For instance, most computers have a keyboard port (currently a Universal Serial Bus USB-like outlet referred to as USB Port), into which the keyboard is connected. Physically identical connectors may be used for widely different standards, especially on older personal computer systems, or systems not generally designed according to the current Microsoft Windows compatibility guides. For example, a 9-pin D-subminiature connector on the original IBM PC could have been used for monochrome video, color analog video (in two incompatible standards), a joystick interface, or a MIDI musical instrument digital control interface. The original IBM PC also had two identical 5 pin DIN connectors, one used for the keyboard, the second for a cassette recorder interface; the two were not interchangeable. The smaller mini-DIN connector has been variously used for the keyboard and two different kinds of mouse; older Macintosh family computers used the mini-DIN for a serial port or for a keyboard connector with different standards than the IBM-descended systems. Electrical signal transfer Electronically, hardware ports can almost always be divided into two groups based on the signal transfer: Analog ports Digital ports: Parallel ports send multiple bits at the same time over several sets of wires. Serial ports send and receive one bit at a time via a single wire pair (Ground and +/-). After ports are connected, they typically require handshaking, where transfer type, transfer