A peripheral device is any auxiliary device that connects to and works with the computer to either put information into it or get information out of it.
A peripheral device may also be referred to as an external peripheral, integrated peripheral, auxiliary component, or I/O (input/output) device.Logitech Mouse.
What Defines a Peripheral Device?
Usually, the word peripheral is used to refer to a device external to the computer, like a scanner, but the devices physically located inside the computer are technically peripherals, too.
Peripheral devices add functionality to the computer but aren't part of the "main" group of components like the CPU, motherboard, and power supply. However, even though they're often not directly involved with a computer's main function, it doesn't mean that they aren't considered necessary components.
For example, a desktop-style computer monitor doesn't technically assist in computing and isn't required in order for the computer to power on and run programs, but it is required to actually use the computer.
Another way to think about peripheral devices is that they don't work as standalone devices. The only way they work is when they're connected to, and controlled by, the computer.
Types of Peripheral Devices
Peripheral devices are categorized as either an input device or an output device, and some function as both.
Among these types of hardware are both internal peripheral devices and external peripheral devices, either type of which might include input or output devices.
Internal Peripheral Devices
Common internal peripheral devices you'll find in a computer include an optical disc drive, a video card, and a hard drive.
In those examples, the disc drive is one instance of a device that's both an input and an output device. It can not only be used by the computer to read information stored on the disc (e.g., software, music, movies) but also to export data from the computer to the disc (like when burning DVDs).
Network interface cards, USB expansion cards, and other internal devices that might plug in to a PCI Express or other type of port, are all types of internal peripherals.
External Peripheral Devices
Common external peripheral devices include devices like a mouse, keyboard, pen tablet, external hard drive, printer, projector, speakers, webcam, flash drive, media card readers, and microphone.
Anything that you can connect to the outside of a computer, that typically doesn't operate on its own, could be referred to as an external peripheral device.2:06
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More Information on Peripheral Devices
Some devices are considered peripheral devices because they can be separated from the primary function of the computer and can usually be removed rather easily. This is especially true of external devices like printers, external hard drives, etc.
However, that isn't always true, so while some devices might be considered internal on one system, they could just as easily be external peripheral devices on another. The keyboard is one great example.
A desktop computer's keyboard can be removed from the USB port and the computer will not stop working. It can be plugged in and removed as many times as you want and is a prime example of an external peripheral device.
However, a laptop's keyboard is no longer considered an external device since it's definitely built-in and not very easy to remove.
This same concept applies to most laptop features, like webcams, mice, and speakers. While most of those components are external peripherals on a desktop, they're considered internal on laptops, phones, tablets, and other all-in-one devices.
You'll sometimes see peripheral devices categorized as input devices and output devices depending on how they interface with the computer. For example, a printer provides output from the computer, so it's considered an output device, while another external peripheral device like a webcam that sends data to the computer, is called an input device.