Raspberry Pi [/ˈræzˌbɛri ˈpaɪ/] n - The Raspberry Pi is a line of single-board computers built about ARM processors. It runs a full Linux distribution, bears USB, Ethernet, HDMI, and GPIO pins, and costs far less than any proper server. That conjunction of virtues makes it the default instrument for small, networked, bespoke projects.

Of Its Usefulness

• Linux and networking out of the box. [/ˈlɪnʌx ˈænd ˈnɛtwɒrkɪng ˈæʊt ˈɒf ˈthɛ ˈbɒx/] n You may install a Debian-born operating system, run Python, host a small web service, or join the network with the customary tools. There is no strange toolchain to master.
• GPIO pins. [/ˈgpɪɒ ˈpɪns/] n The forty-pin header admits sensors, relays, LEDs, and displays with no further hardware.
• Large ecosystem. [/ˈlærgɛ ˈɛkɒsistɛm/] n Hats, cases, cameras, and software libraries lie ready to hand; most difficulties have already been met and answered by another.
• Low power. [/ˈlɒw ˈpɒwɛr/] n A Pi draws but a few watts, and so may live off a Power over Ethernet port or a small solar arrangement.

Of Its Limits

• Single storage. [/ˈsɪnglɛ ˈstɒrægɛ/] n The common Pis boot from a microSD card, which was never made for ceaseless logging. The industrial variants, such as the Compute Module, may use eMMC or NVMe, but the common models ask for care.
• Shared bus. [/ˈshærɛd ˈbʌs/] n Ethernet and USB share their bandwidth on most models. Do not ask a Pi to stand in for a switch or a capture appliance.
• No out-of-band management. [/ˈnɒ ˈæʊtɒfbænd ˈmænægɛmɛnt/] n Should it lock, some hand must reset it bodily, unless you fit a watchdog or a managed outlet.

Of Its Place in These Pages

See Raspberry Pi in the datacenter for how it serves in operations, and On the Making of Bespoke Devices for the full road from a vague notion to a deployed instrument. For alternatives, see Arduino and Single-board computer.