What is the name for a device that is connected to the computer externally?

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.

These devices might also be referred to as external peripherals, integrated peripherals, auxiliary components, or I/O (input/output) devices.

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 they aren't considered necessary components. 

For example, a desktop-style computer monitor doesn't technically assist in computing and isn't required 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 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.

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What is a Motherboard?

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.

An external storage device, also referred to as auxiliary storage and secondary storage, is a device that contains all the addressable data storage that is not inside a computer's main storage or memory. An external storage device can be removable or non-removable, temporary or permanent, and accessible over a wired or wireless network.

External storage enables users to store data separately from a computer's main or primary storage and memory at a relatively low cost. It increases storage capacity without having to open up a system.

External storage is often used to store information that's accessed less frequently by applications running on a desktop, laptop, server or mobile device, such as an Android or iOS smartphone or tablet.

For PCs, an external storage device often consists of stationary or portable hard disk drives (HDDs), or solid-state drives (SSDs) attached via a USB or FireWire connection, or wirelessly.

For enterprises, an external storage device can serve as primary storage connected to servers through Ethernet or Fibre Channel switches, or as secondary storage for backup and archiving purposes. External storage offers HDD, all-flash and hybrid storage arrays for block-based, file-based or object storage, or a mix of these three protocols known as unified storage. Storage area networks (SANs) for block-level storage and network-attached storage (NAS) devices for file-based storage are examples of external storage.

Another common use case for an external storage device is to transport data between on-site and off-site computer systems.

When moving large amounts of data to the cloud, providers will often use external storage devices in a practice known as cloud seeding. Because moving tens of terabytes of data over a network can take hours or days, customers place their data on an external storage device and then send the device to their chosen provider to copy locally. After the initial seeding, only changed data will move across the network to the cloud for backup, archiving or disaster recovery (DR) purposes.

Types of external storage devices and the pros and cons of each

External storage devices come in many forms, both removable and non-removable. A shared characteristic is that they are nonvolatile and data is stored outside of the computer or multiple computers -- server, desktop, mobile and so on -- reading data from and writing data to them.

External HDD

Common portable and fixed external storage devices include HDDs, a type of magnetic storage, and SSDs, which use flash technology with capacities starting in the gigabyte range to 10 terabytes (TB) and higher.

While the price of flash has fallen, comparable HDDs are still considerably cheaper to buy. Because there are no moving parts to flash SSDs, they are significantly faster and more durable than HDDs. External hard disks and flash drives are often used for data protection, backup, DR and long-term retention purposes.

Intel's 3D XPoint-based Optane solid-state drive

Tape is another type of removable Magnetic storage. The most prevalent tape format today is Linear Tape-Open (LTO). LTO specifications were developed by Hewlett-Packard, IBM and Seagate Technology in 1997.

The first generation of LTO, LTO-1, supported a capacity of 200 GB compressed at a maximum compressed transfer rate of 40 megabytes per second (MBps). The latest generation, LTO-8, supports 32 TB at 1,180 MBps. The roadmap for LTO-9 calls for 62.6 TB at 1,770 MBps.

Linear Tape-Open 8 (LTO-8) tape drive and media

Because the price of HDDs has fallen while capacities have increased, hard disks have largely replaced tape as the main medium for backup. However, tape is still frequently used for archiving and DR because of its portability and ability to hold more data per cartridge.

Enterprises typically back up primary data to HDDs as one secondary storage tier, and then offload data to tape for long-term archiving and DR storage tiers, often using tape libraries with automated cartridge handling.

An automated tape library

Another type of external storage device is optical storage, which writes and reads digital content using a laser. This category includes removable media, such as compact discs (CDs) in formats such as CD-ROM, CD-R and CD-RW, which are basically defunct for computer storage purposes; DVDs with a capacity of 4.7 GB single- and 9.4 GB double-sided; and Blu-ray, with a capacity of 5 GB single-layer and 50 GB dual-layer.

Optical media formats

While more durable than tape, optical storage is slower than hard disk. Optical libraries, or jukeboxes, greatly expand the utility of optical storage when it comes to long-term archiving and DR.

Small and removable USB flash drives and media cards for smartphones, tablets, cameras and so on, are examples of portable and removable external storage devices in a small form factor (SFF).

USB flash drive image

While not a device per se, the cloud is another form of external storage used by enterprises -- for backend as a service, disaster recovery as a service, infrastructure as a service and storage as a service -- and individuals.

Among the most common and useful types of external cloud storage are file sharing services, such as Box and Dropbox.