In this guide 5 sections
Memory cards are sold by capacity, but capacity is the least interesting number on the label. The speed class decides whether your camera drops frames, and the brand decides whether the card still works in a year. This guide decodes the symbols and gives you a two-minute test that catches the fakes flooding the local market.
Reading the label
- Class 10 / U1 — at least 10 MB/s sustained write. Fine for photos, music and documents.
- U3 / V30 — at least 30 MB/s sustained. Needed for 4K video, dashcams and security cameras that record continuously.
- A1 / A2 — app performance rating. Matters only if you install apps to the card on an Android phone.
- "633x" or "up to 100 MB/s" — the read speed, which is the marketing number. Write speed is what video needs, and it is usually lower.
Which card for which job
| Use | Pick | Why |
|---|---|---|
| Phone storage, photos | 64–128 GB, U1 or better — Lexar 633x 64GB | Fast enough for the camera roll, cheap per gigabyte |
| Security camera, dashcam | 64–128 GB, U3/V30 — Hoco 128GB high-speed | Continuous writing needs sustained speed and endurance |
| Action camera, 4K | 128–256 GB, V30 — Lexar 633x 256GB | 4K at 60 fps writes around 12 MB/s without pause |
Pen drives: speed and the two-ended trick
USB 3.x drives copy a film in seconds where USB 2.0 takes minutes; the blue insert in the plug, or "3.0/3.2" on the listing, is the tell. A dual-connector drive such as the SanDisk Ultra Dual Drive Go has Type-C on one end and USB-A on the other, so it moves files between a phone and a laptop without an adapter. For documents you would rather not lose on a bus, the Lexar F35 Pro unlocks with a fingerprint. The Lexar V400 is the plain, fast everyday stick.
The day-one fake test
- Put the card in a phone or laptop and look at the capacity it reports. A "128GB" card showing 119 GB is normal (binary vs decimal); one showing 31 GB is a fake with a rewritten controller.
- Copy a folder of large files — a few films, say 20 GB — onto it, then copy them back and open the last one. Fakes accept the write and then return corrupted files beyond their real size.
- Time the copy. A card sold as U3 that writes at 6 MB/s is not U3.
Do this inside the return window. A genuine card has clean printing, a serial number on the back and a brand whose website lists that exact model.
Making a card last
- Format the card in the device that will use it, not on a PC.
- Eject before removing; pulling a card mid-write is the usual cause of "card not recognised".
- Replace camera and dashcam cards every two years; they are written to constantly and wear out silently.
- Keep a copy of the card's photos on a laptop or a second drive; cards fail without warning, and data recovery services in Dhaka charge more than the card cost.
The storage shelf carries Lexar, SanDisk and Hoco cards and drives, delivered cash on delivery with a 7-day easy return — enough time to run the test above.
Frequently asked questions
Why does my 64GB card show less than 64GB?
Manufacturers count 1 GB as 1,000 MB and computers count 1,024, so a 64GB card shows about 59 GB. A card showing far less, such as 8 or 30 GB, is a fake.
Which memory card class for a security camera?
U3 or V30 with a high-endurance rating, because the camera writes to it all day. A plain Class 10 card wears out in months.
Is a USB 3.0 pen drive worth the extra cost?
Yes if you copy large files — it is five to ten times faster than USB 2.0 and works in any USB port.
Can I move apps to the memory card?
On many Android phones yes, if the card is A1 or A2 rated. Apps on slower cards open noticeably slower.
