SD and microSD Cards Explained: Speed Classes, Capacity and What to Buy

The hardest part of buying an SD or microSD card isn’t the capacity — it’s decoding the maze of speed-class logos stamped on it. Those little symbols decide whether your camera can shoot 4K without stuttering, whether your dashcam drops frames, and how snappy apps feel on a handheld. Buy the wrong class and a big, cheap card can quietly bottleneck an expensive device.

For South African buyers kitting out cameras, dashcams, drones, phones, handheld consoles or a Raspberry Pi, matching the card’s speed rating to the device is what actually matters — capacity comes second.

Key Takeaway: Match the card to what the device writes. For 4K video look for a V30 (or higher) rating; for smooth app performance on phones and handhelds look for A1/A2; and buy from reputable brands — counterfeit high-capacity cards are common and fail fast.

SD Card Ratings at a Glance

What the Speed Ratings Actually Mean

The big number on the front (like “170MB/s”) is the best-case read speed — but the small class logos tell you the guaranteed write speed, which is what matters for recording. Video Speed Class (V30, V60, V90) is the clearest modern rating for video: V30 sustains at least 30MB/s. For app-heavy devices, the A1/A2 ratings describe random read/write, which keeps apps and games responsive.

Match the Card to the Device

Different jobs stress the card differently:

• 4K cameras & drones: V30 minimum, V60/V90 for high-bitrate or slow-motion.
• Dashcams & CCTV: high-endurance cards built for constant rewriting, not standard cards.
• Phones & handhelds (e.g. Switch): A1/A2 + U3/V30 for fast app loading and storage.
• Action cameras: V30 and the brand’s recommended card list.
• Raspberry Pi: A1/A2 random performance matters more than headline speed.

Capacity, SDHC vs SDXC and Device Limits

Bigger isn’t always usable — check your device’s maximum supported capacity. SDHC covers cards up to 32GB; SDXC covers 64GB and above (and uses the exFAT file system). An older camera or dashcam may not read a very large SDXC card, so confirm the device’s limit before buying a 256GB or 512GB card.

Beware Counterfeit Cards

Fake high-capacity cards are one of the most common scams in memory storage. They report a large size but actually hold far less, corrupting data once “full.” Buy from reputable brands and trusted retailers, be sceptical of prices that look too good, and consider a quick capacity-test after purchase. A genuine, correctly-rated card is cheaper than the photos or footage you’d lose.

Which Card Should You Buy?

Key Takeaway: A huge card with a low speed class is the wrong buy — a dropped-frame 4K recording or a laggy handheld is the result. Read the small logos (V-rating for video, A-rating for apps), confirm your device’s capacity limit, and stick to genuine cards.

How to Buy Memory Cards in South Africa

DistriNode stocks genuine SD and microSD cards, high-endurance cards and card readers — matched to your camera, dashcam, phone or handheld, with local stock and fast delivery. Browse microSD cards, SD cards, memory cards, card readers and USB flash drives.

Frequently Asked Questions

What speed card do I need for 4K video?

Look for a V30 rating (or U3, which is equivalent) as the minimum for 4K — it guarantees a sustained 30MB/s write. For high-bitrate 4K, slow motion or higher resolutions, step up to V60 or V90, and always check your camera’s recommended card list.

What do A1 and A2 mean on a microSD card?

A1 and A2 are App Performance Classes describing random read/write speed, which keeps apps and games responsive. They matter for phones, handhelds like the Switch, and Raspberry Pi, where loading lots of small files matters more than headline sequential speed.

Why is the card’s real speed slower than the number on the front?

The big number (e.g. 170MB/s) is the best-case read speed under ideal conditions. The smaller class logos (U3, V30, A2) state the guaranteed minimums — especially for writing, which is what matters when recording video. Always buy on the class rating, not the headline figure.

How do I avoid fake memory cards?

Buy from reputable brands and trusted retailers, and be wary of large-capacity cards priced suspiciously low. Counterfeits report a false size and corrupt data once truly full. A quick capacity-test app after purchase can confirm a card holds what it claims.

Sources

• SD Association — speed classes
• Kingston — memory card speed classes explained