Choosing the correct SD Card

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Choosing the correct SD Card

Post by Floyd » Tue Oct 02, 2018 9:30 am

A SD card will normally work in a SDHC device (possibly with lower performance). SD cards are in the following capacities 4,8,16,32,64,128,256 512MB and 1GB, 2GB only. Currently mainly 2GB SD cards are being sold.

A SDHC card will not work in a SD device such as a camera or reader. SDHC cards are in the following capacities 4GB, 8GB, 16GB and 32GB

SDHC (Secure Digital High Capacity) was established to meet the growing demand for HD (High Definition) video and high resolution image recording now used in many SD-enabled devices.

SDHC is the same physical size and shape as standard SD but meets the new SD specification of version 2.0. If the SD card is 4GB or above, it is classed as a SDHC card. Currently, SDHC specifications allow for memory cards of a capacity between 4GB and 32GB.

SDA (SD Card Association) has also established a Speed Class rating (Class 2, 4, 6 and 10) for the standardisation of data transfer speeds (compulsory for SDHC cards):

CLASS 2 - a guaranteed minimum write speed of 2MB/s or higher*
CLASS 4 - a guaranteed minimum write speed of 4MB/s or higher*
CLASS 6 - a guaranteed minimum write speed of 6MB/s or higher*
CLASS 10 - a guaranteed minimum write speed of 10MB/s or higher*
* The minimum speed capability depends on the manufacturer of the host device and model.

All Class 2, Class 4, Class 6 and Class 10 SDHC cards are compatible with SDHC devices. Please note that if the device manual suggests a SDHC card of speed Class 4 as a minimum, the user should install a Class 4, Class 6 or Class 10 (faster) SDHC, NOT a Class 2 card as this may reduce performance of the device.

SDHC cards are not backwards compatible with standard SD devices, so they may not work in digital cameras or USB Memory Card Readers manufactured before summer 2007.

There are also two Ultra High Speed (UHS) speed classes–1 and 3—but they’re more expensive and are designed for professional use. UHS cards are designed for devices that support UHS.

Here are the associated SD class speed logos, in order from slowest (class 2) to fastest (UHS class 3):

SD card speed class 2 SD card speed class 4 SD card speed class 6 SD card speed class 10 SD card UHS class 1 SD card UHS class 3


You’ll probably be okay with a class 4 or 6 card for typical use in a digital camera, smartphone, or tablet. Class 10 cards are ideal if you’re shooting high-resolution videos or RAW photos. Class 2 cards are a bit on the slow side these days, so you may want to avoid them for all but the cheapest digital cameras. Even a cheap smartphone can record HD video, after all.

An SD card’s speed class is identified on the SD card itself—just look for the logo. You’ll also see the speed class on the online store listing or on the card’s packaging when purchasing it. For example, in the below photo, the middle SD card is speed class 4, while the two other cards are speed class 6.

If you see no speed class symbol, you have a class 0 SD card. These cards were designed and produced before the speed class rating system was introduced. They may be slower than even a class 2 card.

Physical Size
SD cards also come in different sizes. You’ll find standard SD cards, miniSD cards, and microSD cards.

Standard SD cards are the largest, although they’re still pretty small. They measure 32x24x2.1 mm and weigh just two grams. Most consumer digital cameras for sale today still use standard SD cards. They have the familiar “cut corner” design.

miniSD cards are smaller than standard SD cards, measuring 21.5x20x1.4 mm and weighing about 0.8 grams. This is the least common size today. miniSD cards were designed to be especially small for mobile phones, but now that we have an even smaller size—microSD—miniSD cards aren’t too common.

microSD cards are the smallest size of SD card, measuring 15x11x1 mm and weighing just 0.25 grams. These cards are used in most cell phones and smartphones that support SD cards. They’re also used in many other devices, such as tablets.

Choosing a size is really just about what fits into the device you have. SD cards will only fit into matching slots. You can’t plug a microSD card into a standard SD card slot. However, you can purchase adapters that allow you to plug a smaller SD card into a larger SD card’s form and fit it into the appropriate slot. Below, you can see an adapter that lets you use a microSD card in a standard SD card slot.


Like USB flash drives, hard drives, solid-state drives, and other storage media, different SD cards can have different amounts of storage.

But the differences between SD card capacities don’t stop there. SD Standard Capacity (SDSC) cards range in size from 1 MB to 2 GB (and sometimes even 4 GB—although that’s not standard). The SD High Capacity (SDHC) standard was created later, and allows cards 2 GB to 32 GB in size. An even more recent standard, SD Extended Capacity (SDXC) that allows cards 32 GB to 2 TB in size.

I hope this helps. If you want to shoot 4K video in your Nikon D7500 for instance, you will need a very fast SD Card. Otherwise your video will be interrupted after a second or two waiting for the camera to write to the card. To shoot a successful video the camera must be able to continuouslky write to the sd card without pausing. If your SD Card is too slow to accept continuous writing of 4K you will have to reduce the resolution you are shooting to a level that the camera can write continuopusly to the card successfully.

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