What Is an SD Card? Types, Sizes, and Choosing the Right One
What is an sd card, exactly? It’s a Secure Digital memory card — a small, removable flash storage device used in cameras, phones, tablets, drones, and hundreds of other devices to store photos, video, audio, and other data. What is a sd card in practical terms: a portable storage unit that holds your files the way a hard drive does, but in a format small enough to fit between your thumb and index finger. Understanding what is sd card technology and how different camera memory card types compare helps you choose the right card for your specific gear and shooting style.
This guide covers the main camera memory card types, when a 200gb sd card makes sense versus smaller options, and how speed class ratings affect real-world performance in cameras and video recorders.
SD Card Types and Form Factors
SD, SDHC, and SDXC
The answer to what is an sd card requires distinguishing between three capacity standards. A standard SD card tops out at 2 GB. SDHC (High Capacity) covers 4 GB to 32 GB. SDXC (Extended Capacity) covers 64 GB to 2 TB. Most cameras manufactured since 2010 use SDHC or SDXC. If you’re buying a 200gb sd card (technically 256 GB — manufacturers round), you’re buying SDXC format.
Physical form factor is a separate question from capacity. Full-size SD cards are 32x24mm. MicroSD cards are 15x11mm and are used in phones, drones, and action cameras. MicroSD cards can be used in full-size SD slots with an included adapter. When asking what is a sd card for a specific device, check both the capacity standard (SDXC vs SDHC) and the physical size requirement in your device’s manual.
Speed Classes and What They Mean
Camera memory card types are differentiated by speed class ratings that indicate minimum write speeds. UHS Speed Class 1 (U1) guarantees at least 10 MB/s write — adequate for JPEG photography. UHS Speed Class 3 (U3) guarantees at least 30 MB/s — required for 4K video recording. Video Speed Class (V30, V60, V90) ratings align more precisely with what modern cameras need: V60 cards support 8K RAW capture on compatible cameras, while V90 cards support the highest bitrate professional video formats.
When evaluating what is sd card speed for your camera, check the camera manufacturer’s recommended minimum write speed. Sony a7 series bodies typically require V60 for continuous RAW burst shooting. Canon R-series bodies may only need U3/V30 for standard 4K. Buying a card faster than your camera can use doesn’t hurt, but it’s unnecessary spending.
When a 200GB SD Card Makes Sense
A 200gb sd card is appropriate for shooters who produce high file volumes — wedding photographers shooting all-day events in RAW, videographers working in 6K or 8K, or wildlife photographers running continuous burst sequences. At typical RAW file sizes of 25 to 50 MB, a 200 GB card holds 4,000 to 8,000 RAW images before filling. That covers most single-day shoots without swapping cards.
The tradeoff with a 200gb sd card (or larger) is the consequence of failure. All camera memory card types can fail, but a larger card concentrates more data in a single point of failure. Many professional photographers split their shoots across two smaller cards rather than using one large card — most mirrorless cameras with dual card slots can write to both simultaneously as a real-time backup.
Understanding what is an sd card beyond the basics — speed ratings, capacity limits, and form factors — helps you match storage to your actual workflow. A 200gb sd card for video production makes clear sense; the same card for occasional family photography creates unnecessary risk without meaningful benefit. Match the card to what you actually shoot.
Bottom line: What is an sd card comes down to capacity, speed class, and form factor. Know your camera’s minimum write speed requirement, choose camera memory card types rated for your highest-demand shooting scenario, and consider a 200gb sd card only if your file volume and camera slot count justify it.