Memory cards come in all shapes and sizes depending on your device whether it be a digital camera, mobile phone or a digital video camera but what comes down to it we all need one.
One thing that does differ is the class or performance of these memory cards that can make a huge difference on what you are using it for. Obviously when recording video, you do not want to end up with a slow card which could cause potential problems like jittering or recording with a lower quality image due to performance concerns.
What do these Class numbers mean?
A class is the minimum write speed rating for the memory card and what it can be used for is dependent on the device you are using it for. For example you would not want to use a class 4 card when it comes to recording video because the card will not be able to keep up, but a class 4 could work well enough to take pictures with a digital camera.
It is easy to identify the class of a card as it is usually a number encompassed by a C. This number indicates the class of the card where lowest 2 and to date, 10 is the highest. The image to the right shows you the class number (in this case 6) and the size of the card being 32 Gigabytes.
In this case a Class 6 card is rated at a minimum of 6 Megabytes (MB) per second whereas a Class 4 card would be a minimum of 4 MB/s, etc…
Some manufacturers use different speed systems to rate their cards to make it harder on consumers to decipher what they should be using for their device. Some manufacturers might mark on their cards for example 133X instead of using a similar class number.
What does the X mean?
The speed rating X was taken from CD-ROM speed standard which is a slow 150KB/sec (or 0.15MB/s). In order to find out the minimum performance of a card we will have to do a little bit of math.
If a card is rated at 133X we would then do 133 x 0.15 ~ 20MB/s. This is the minimum write speed a card will be able to process. The higher the X rating the quicker it can write while reducing the time to write it to the memory card.
Some manufacturers label the cards with both class and the X rating to make it easier to identify the card you are getting.
The image to the right shows you both the Class and the speed rating in X at the bottom. Note that even though it is a class 10 card, the 100X rating turns into a minimum write speed of 15 MB/s (100 x 0.15= 15MB/s). As stated above a Class 10 card is a minimum write speed of 10MB/s.
High End Cards
There is a new breed of cards that are out based on a new standard which is developed more for HD video recording called Ultra High Speed class, UHS for short. These cards are extremely fast as it is needed when recording high definition video at very high quality.
These cards have higher minimum write speeds which is definitely needed to ensure continuous recording of high definition video. These cards also come in higher capacities like due to the size needed when recording high definition video and also come at a higher price premium
The image to the right shows you one of the UHS cards that are available on the market, and as mentioned throughout the article, it is noted as a class 10 device and also uses the X speed (here it is at 600X) and now a new symbol that encompasses the 1 which is the U which stands for UHS.
This card guarantees us a minimum of 90MB (0.15MB X 600) and if the device supports it can record to the card with minimal time in between images.
SDHC vs SDXC
As you can see from the images included in this guide, you can see there are two acronyms on the SD cards one is SDHC and the other is SDXC. Without going into much technical detail SDHC’s maximum size of card is 32GB whereas SDXC’s minimum capacity is 32GB up to 2TB.
The file format of an SDXC card is called ex-FAT whereas SDHC is FAT32.
So what card should you use? It depends on your device. An older digital camera might not be able to take advantage of the faster memory cards or might not be able to read the SDXC cards where it could only read SDHC.
For SD or HD video a class 10 is a must. Video recording needs more time to write the file so a faster card would reduce the time it take to write to it. If you have a brand new HD videocamera, then you might be able to use the UHS type cards which guarantees a high write speed but at the cost of a higher price point.
The class and X speed ratings are the same whether you are using a standard, mini or micro form of these cards.