Also known as: Secure Digital, microSD
An SD card (Secure Digital) is a small removable storage card built around flash memory, widely used in cameras, phones, and small computers.1
Overview
The standard defines several physical sizes — full-size SD, miniSD, and the tiny microSD — and capacity tiers that grew over time: SDHC, SDXC, and SDUC. A small controller inside the card handles wear leveling and presents a simple block device, so the host just sees storage formatted with a file system. Speed classes (Class 10, UHS, V30, and so on) rate sustained write performance, which matters for high-bitrate recording.
Where it fits
The SD card is the default boot and storage medium for many single-board computers, including the Raspberry Pi, which boots from a microSD card by default. It is cheap and removable, but cards vary in quality and endurance, and a low-end card can wear out under constant logging. A GopherTrunk capture node can run from an SD card, though for heavy continuous writes an eMMC module or an SSD lasts longer.