The newemerged in January, and Toshiba now promises the cards themselves will begin arriving about a year afterward.
Toshiba said Monday it expects to be the first to bring SDXC cards to market, with testing samples of a 64GB version shipping in November and the real thing shipping in the spring of 2010. Those dates will be key moments in what doubtless will be a gradual transition away from the prevailing SDHC standard.
SDXC backers promise higher capacities and data transfer speeds for SDXC, which is important for devices such as video cameras that can produce lots of data at a sustained rate. But initially, a new generation of Toshiba's SDHC line will match the SDXC's maximum 60MBps data-reading speed, and maximum 35MBps data-writing speed, the company announced, using a new high-speed interface called UHS104.
The fast new SDHC cards, though, will only be available in 16GB and 32GB models. SDHC tops out at 32GB, but the SDXC specification extends to 2TB. In addition, through use of Microsoft's exFAT files system on SDXC cards, individual files can exceed 4GB, which is important for longer videos.
Capacity is undeniably important when it comes to carrying your video camera around for extended periods of time. But do you really need all that transfer speed? Leaving aside theand certification, even high-definition video only pushes the envelope so hard.
For example, Canon's high-end 5D Mark II SLR, which can record 1080p video at 30 frames per second, requires only a relatively modest 8MBps write speed for its CompactFlash card; high-end CompactFlash today can handle 45MBps.
Of course, there's also the matter of transferring photos and videos to computers, a tedious task at best that benefits from maximum speed. But that's often constrained, though, by the card reader and its interface to the computer.
No doubt those pipes will widen as time marches on, with SDXC and higher-speed SDHC helping to nudge things along on one end and higher-speed interfaces such as USB 3.0 and Firewire S1600 and S3200 on the other end. The SDXC specification calls for 104MBps speeds in 2009 and eventual speeds of 300MBps.
One interesting issue is whether SDXC will displace CompactFlash in high-end SLRs. SDHC is used in lower-end SLRs now, displacing CompactFlash, and is making its way into higher-end models including Nikon's D300s and Canon's 1D Mark III alongside CompactFlash.
SD and its successors have relegated rivals such as xD card from FujiFilm and Olympus and Memory Stick from Sony to product niches, new MacBook Pro laptops from Apple have built-in SD card slots, and Canon USA technical adviser .
So SD has plenty of momentum, and the SDXC generation certainly has the potential to continue to outpace CompactFlash in price while also becoming competitive in capacity and data transfer speeds.
The diminutive size of SD compared to CompactFlash is an asset when trying to squeeze a slot into a computer or camera. But some serious and professional photographers have griped that the small cards are hard to handle and easy to lose.