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Demystifying SD Memory Cards...Some More

A while ago we posted information we had received from SanDisk about memory cards, called Memory Card Myths Demystified. We continue to get many questions regarding memory cards, especially Secure Digital (SD) cards. The greatest confusing factors are the designations we all see on the retail packaging and printed on the individual memory cards themselves.

Secure Digital (SD) Memory Cards

What is the difference between SD, SDHC, and, now, what the heck is SDXC? A standard SD card has a memory capacity up to 2GB (2,048 MB). SDHC memory cards begin with a memory capacity above 2GB and end at 32GB. SDXC is a more recent designation that simply indicates cards with a capacity over 32GB and up to 2TB (2,048GB, 2,097,152MB). These designations simply indicate the potential memory capacity of the card. That's it.

But it gets more confusing because why even worry about these designations in the first place? Why care if SDHC cards could potentially be 4GB, 8GB, 16GB or even 32GB? The short answer is compatibility. SDHC cards are not compatible with older cameras that were manufactured when standard SD cards were the norm. If you were to try to use a SDHC card in a non-compatible camera, the camera would not work. You would be provided with an error of something like "card read error", and the camera would be locked up. So, it is important to know if your camera can handle, say, a 4GB memory card. And, the same is true with SDXC memory cards. If you have a camera that is not compatible with this capacity card, it will not work. So, before you go out to purchase the latest 64GB card for your digital camera or camcorder, you should first reference the manual to see if the device is compatible. Now, newer cameras are backwards compatible. That means you can use a 2GB memory card with a camera that is SDHC, or even SDXC compatible.

The frustration a lot of consumers are currently experiencing involves availability of some smaller capacity SD cards. Not too long ago, it used to be difficult to find 1GB memory cards, and now you almost see them nowhere. That is not so much a problem considering you can just purchase a 2GB memory card, and the only downside (or upside depending on who you are and how you look at it) is that you will have more capacity for storing your images and/or video. Now, like the 1GB cards, it is starting to be difficult to find 2GB memory cards. But why, you may ask? It is starting to cost more to manufacture 2GB memory cards than it is to make 4GB memory cards. With higher megapixel cameras and HD video becoming the norm, consumers are purchasing larger cards. There is no longer a large enough market to support the lower prices of the 2GB cards, so we slowly see them being phased out. The big problem that is occurring that did not happen when 1GB memory cards were being phased out is that a 4GB SD card is an SDHC card, and is therefore not backwards compatible with older cameras. If you have an older camera and you need a memory card, you are starting to run into trouble. We still carry 2GB memory cards, and hope to carry them for a while. They are starting to cost us more than 4GB memory cards, but we have yet to raise the price.

The other designation we see customers having a difficult time with are speed classes. Like the capacity designations mentioned above where SDHC indicates a capacity range, speed classes just indicate the speed (read and/or write) of the memory card. Speed classes for still photography, and shooting still photographs, is not as critical a point as it is for video. Most cards will indicate the max burst speed of the memory card in either MB/s (megabytes per second) or an "x" factor. Although these cards can achieve these speeds in bursts, like in saving a smaller still picture from a camera to the memory card, these indications do not tell the whole story, especially when thinking about video and larger transfers.

In order to understand the sustained speed of a card, you need to look at how the "class" is designated. The speed classes are very easy because they are self-explanatory. A card labeled "Class 2" has a sustained write speed of at least 2MB/s, a "Class 4" card is at least 4MB/S, "Class 6" 6MB/s, and so on. This is important for video because, although it is OK in most situations for a card's speed to fluctuate while still images are being written, it is not OK for a card's speed to dip below a minimum while recording video. If you are shooting video and a memory card dips below the necessary sustained write speed for that device, the camera will "drop" frames and the video will suddenly appear choppy. On the other hand, with still photography, the still image has already been written and is simply being sent to the card from the camera's buffer. If it takes a little more time, so be it, the image is not jeopardized.

Note how we italicized "at least" above. A memory card that is Class 2, may be much faster in bursts, or could be even faster in terms of sustained speeds, but at a minimum it is 2MB/s. How do you know how fast the card must be for your device? Simply check the manufacturer's specifications in the manual or elsewhere. The manufacturer will designate the minimum class that will be required for smooth video and operation. Also, keep in mind that high speed cards can be very useful for every day use beyond shooting video. If you are like most people, you probably wait to transfer your images until after you fill up an entire card. If you have a 16GB card, transferring all of that data can take a long time. To save yourself time and frustration, you may want to consider a faster speed card to save yourself having to wait around while your images transfer from your card to your backup device, like your computer.

Now that you feel more confident with speed classes, some of the latest cards use UHS (Ultra High Speed) bus interface technology. As high-definition video digital SLRs and larger resolution digital video devices start to become the norm, this technology with faster transfer speeds will be more widely used and expected. UHS cards are currently either designated with UHS-I and UHS-II, and the transfer rates go up to 312 MB/s. Before you rush out to get these ultra-fast cards, keep in mind that only a couple of cameras are currently compatible, like the Nikon D7000, and your card reader may not be able to take full advantage of the speed. But, these cards are backwards compatible and can offer faster transfer rates than other cards, even with non-UHS compatible devices. If you are interested in a UHS SD memory card, our most popular selling card is currently this one made by SanDisk. In addition, a great resource for information on SD memory cards is the SD Association website.

What prompted this post in the first place was actually a thread in a forum regarding the Hoodman RAW Steel SD memory cards. All of the Hoodman promotional images of these cards show them without a write-protect tab. Someone in a forum wanted to know if they do have one, and we got in on the conversation to confirm that they do. Shortly thereafter someone wanted to know the speed of these cards. Hoodman has not been good about publishing significant speed information like some other manufacturers do, but they do indicate them as Class 10 cards. We were therefore curious how the Hoodmans stacked up against some other cards in terms of speed, and decided to put them through a simple test.

We gathered a handful of memory cards lying around our retail store. We have dozens of display cameras, and always have some extra SD cards lying around, so we took those for testing. We also grabbed a Hoodman RAW Steel SD memory card to see how it fared. We could have simply tested the Hoodman by itself, but we were curious to see how cards compare to how they are advertised. See below for the data. Please know that we only tested sustained speeds. We were surprised to see that the two memory cards we tested that indicated being Class 4, were actually much faster. The other cards were pretty much as advertised. The old 128MB Fujifilm card we had was less than a tenth as fast as the fastest card we tried, which turned out to be a Class 4 SanDisk. Although this was only 128MB in capacity, it seemed to take forever to test.

Also, we want to mention that if you haven't already, you may want to check out this post we made on the Hoodman RAW Steel SD memory cards earlier on this blog.

Delkin Devices 2GB SD Memory CardDelkin Devices "Standard" 17MB/s 115x 2GB SD Memory Card

Sustained Write Speed: 5.25 MB/s
Sustained Write Speed: 15.7 MB/s 

Delkin Devices 4GB SD Memory Card

Delkin Devices "Pro" Class 6 22MB/s 150x 4GB SD Memory Card

Sustained Write Speed: 7.70 MB/s
Sustained Write Speed: 18.6 MB/s 

Delkin Devices 4GB SD Memory Card

Delkin Devices Class 4 4GB SD Memory Card

Sustained Write Speed: 8.92 MB/s
Sustained Write Speed: 16.1 MB/s

Fujifilm 128MB SD Memory Card

Fujifilm 128MB SD Memory Card

Sustained Write Speed: 1.47 MB/s
Sustained Write Speed: 6.83 MB/s

 

Hoodman RAW Steel SD Memory Card

Hoodman RAW Steel 4GB SD Memory Card

Sustained Write Speed: 10.3 MB/s
Sustained Write Speed: 18.5 MB/s

 

Sandisk Ultra SD Memory Card

SanDisk Ultra Class 4 15MB/s 2GB SD Memory Card

Sustained Write Speed: 10.6 MB/s
Sustained Write Speed: 18.7 MB/s

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