We’ve only just barely begun to accept SDHC as our new de facto standard for high capacity card memory storage when… what? Another standard’s out?
Before you toss your camera out in a fit of rage, sit down and consider for a moment that this is a terrific development. It’s called SDXC, and it’s already trickling out into the market.
Memory cards are also known as flash cards. This is because the core technology behind these cards is known as flash memory, so called because in the old days, these kinds of memory were erased using a flash of ultraviolet light. These days no flash of light is necessary, but the name stuck.
History, however, is chock-full of memory card formats that came and went. There’s SmartMedia, my first memory card — nobody remembers this relatively huge format, and for good reason: it went only to 128MB max. There’s the MMC, which was eventually gobbled up by SD. And there’s Sony’s Memory Stick, which Sony is now quietly abandoning.
There’s also the PC Card (a.k.a. PCMCIA), which is more an interface than a storage device, and can be thought of more as a descendant of gaming cartridges than as an ascendant of card memory. And of course there’s the CompactFlash or CF card, which is also slowly vanishing from the market.
But the hands-down winner today is the Secure Digital format, which is controlled by the SD Association. Secure Digital is the standard behind the SD card and all its descendants.
It keeps going
The original SD card was designed back in 1999 and was a direct evolution of the MMC or MultiMedia Card format. It was designed –get this– to compete head on with Sony’s then-new Memory Stick format. Over the next several years, SD won out due to its size and capacity, and eventually beating the relatively huge CF cards that used to be popular with DSLR photographers.
The secret to SD’s longevity is that the format has evolved over time. From the original SD card specifications, the SD Association eventually produced smaller card formats to tie in with the growing mobile market. First as the miniSD card, and then in the form of the even smaller microSD format (see right).
And if they try to come up with an even smaller format, we’re gonna be needing tweezers to carry them around.
But it’s not just the size that evolved. Speed and performance evolved as well.
Today, SD cards are sold side by side with the newer SDHC format. SDHC stands for SD High Capacity, and is also lesser known as SD 2.0. The format came about in 2006 as a way to ramp up the speed and storage capacity of the SD format.
SDHC devices are backwards compatible, so they’ll read SD cards. But an SD card reader won’t read SDHC cards. So if you’re buying a card reader, make sure it can read SDHC.
Know your speed limits
SD cards have a maximum official capacity of 2GB (though up to 4GB is possible), and speeds of anywhere from a puny 600KB/s (600 kilobytes per second — about 10 seconds to download a single MP3 song) to 20MB/s (four songs a second) for high-end pro cards.
SDHC, on the other hand, can store up to 32GB (officially), and have speeds currently topping at 80MB/s for reads and 10MB/s for writes.
How do you figure out the speed of a card? Read the label.
Standard SD cards use speed ratings that are based on CD-ROM speeds. Yup, how quaint. So when an SD card says that it has 16x speed, that’s equivalent to the speed rating on a CD-ROM drive. And you know how slow CD-ROMs are, so don’t be too impressed too fast. You’d want 66x or more for reasonable speeds.
SDHC cards, however, use a different speed rating that’s based on speed classes (see right). You’ll know that a card is SDHC if it has the Class rating stamped on it.
Class ratings are based on write speeds, in MB. Note that it takes longer to write to flash memory than it is to read from it. In the case of SDHC, reads are typically 8 times faster than writes. So a Class 2 card can write 2MB/s and read 16MB/s. And a Class 4 card can write 4MB/s and read 32MB/s.
The faster the better, of course. So you’d want a Class 6 for good device performance in video cameras and computers. For digital cameras, however, a Class 4 is good enough since the data requirements aren’t as intensive.
So SDHC seemed to be the state of the art, and people were happy. But not for long.
And now, SDXC
Industrial demands for speed and capacity, especially from video content providers, led to the thirst for even more speed and capacity. So now, the SD Association has unleashed SDXC.
SDXC stands for SD Extended Capacity (or Exteme Capacity, if you’re a hipster).
Remember how SDHC can officially store up to 32GB? Well, SDXC can go up to 2TB! (That’s terabytes to you.)
The first SDXC cards were unveiled in 2009, initially at capacities of 64GB. Thus far, SDXC cards are rated at Class 10. That’s 10MB/s writes, and 80MB/s reads. If you see a Class 10 rating on a card, you can bet that it’s an SDXC card.
But that’s just scratching the surface, because the SD Association is promising speeds of up to 300MB/s.
The thing is, while the first 64GB SDXC cards at Class 10 can be read by current SDHC drives, the honeymoon won’t last for long. Inevitably, the next SDXC cards will scale up to a different communication standard that will require SDXC drives. You’ll then need to upgrade your card readers yet again.
To the right, you’ll see a sample of an SDXC card. You will notice that the Class 10 symbol is there at the bottom right. It’s a sign that even if it’s an SDXC card, you can nevertheless still use this with an SDHC card reader.
Above it, however, is the letter I, above which is a letter U with a number in it. This is the sign of things to come: it stands for the UHS-I standard, which you can bet stands for Ultra High Speed. The number in the U-shaped symbol tells you that this is a Class 1 device under the UHS-I standard.
The UHS-I speed standard is different from the Speed Class standards of SDHC, so you’ll be seeing these two symbols side by side in the first batch of SDXC cards. But soon, as SDXC takes off and goes even bigger and faster, you’ll see the old Class symbol vanish and the new U symbol will dominate. It will be your cue that these cards will no longer be compatible with the older SDHC drives.
Since UHS-I Class 1 is equated to a Class 10 under the old standard, this means that UHS-I offers 10MB/s write speeds. Which means when UHS-I Class 2 comes out, it will offer 20MB/s write speeds, and so on.
So what can you expect from SDXC in the future? Well, aside from eventually offering 2TB of storage tops, expect it to eventually reach speeds of over 300 megabytes per second (300MB/s)! That would be UHS-I Class 30.
Looks like we have our new champion standard for now. At least until the industry gets restless once again and decides it wants 100TB of storage on a stamp-sized card…
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