Apple’s Tilt to SD Cards Looking Smarter Than Ever

Last month I commented that Apple’s substitution of Secure Digital Card (SD) slots for ExpressCard slots in the 15″ MacBook Pro made considerably good sense. It would be nice to have both, but the ExpressCard support wasn’t being heavily used, according to Apple, while SD was growing more popular. The 13″ MacBook Pro also gets an SD slot where the preceding unibody MacBook was slotless, so it’s pure value-added there.

However, as I learn more about the Secure Digital format, both what’s already available and what’s coming, I’m even more convinced that Apple made the right call.

For one thing, while ExpressCard 34 cards are smaller than the old PCMCIA CardBus cards they replaced, the standard SD Card format measures 32mm x 24mm in footprint (roughly the viewing area of a 35mm film negative or slide) vs. 75mm x 34mm for the ExpressCard, and it is only 2.1mm thick. That is especially helpful in computers as thin as Apple’s MacBook family — even more so if Apple builds a tablet or notebook smaller than the MacBook Air.

Another SD Card advantage is hardware standardization. The SD format shows potential for becoming the standard for removable storage in portable computers. The majority of PC laptops, and most netbooks, are available with SD Card slots, so Apple is no longer the odd man out in that context. Apple portables honcho Todd Benjamin told PCMag’s Mark Hachman in an interview that one reason the company went SD is that the format has become “really ubiquitous,” and not just in laptops. Consistent with Apple’s focus on consumer electronics and Mac market positioning as a digital hub, SD Card support is built into a myriad of consumer digital devices, especially cameras and Mobile Internet Devices (MIDs).

The iPhone doesn’t support removable storage as of yet, but in my opinion, it’s virtually inevitable that it will, and when it’s added, the tiny Mini SD variant (15mm x 11mm) is a likely bet.

SD Cards Just Have More to Offer

Currently, standard SD Card storage capacity tops out at a modest 4GB, but a much higher capacity variant, called SDHC, offers up to 32GB, and an eXtended Capacity SDXC spec that was unveiled at this year’s Consumer Electronics Show supports memory capacities above 32GB up to a potential 2TB, with data transfer speeds up to 104MB/sec and potential future throughput up to 300 MB/sec. The SDXC standard uses Microsoft’s exFAT file system (FAT64). Existing SD and SDHC host devices won’t be compatible with the new SDXC cards, but SDXC host devices will be backwards-compatible to work with SD and SDHC cards. A microSDXC card also is reportedly in the works for use in small mobile devices, with plenty of development headroom apparent in the SD format.

Cards conforming to SD (4MB to 4GB) and SDHC (4GB to 32GB) standards are supported by the slots in the new MacBook Pros. MultiMediaCards (MMC) can also be used in this slot, while MiniSD, MicroSD, and higher density formats like MiniSDHC and MicroSDHC can work but require “passive” adapters that conform to the standard SD width and thickness specifications.

MacBook Pro SD Card slots support a maximum throughput of 240Mbit/s, which exceeds the transfer rate of most SD media (about 17-21Mbit/s to 30Mbit/s, depending on type) by a substantial margin. MacBook Pros recognize cards inserted in their SD card slots as USB storage devices that can be mounted, read from, and written to as with any other USB storage device.

You can even make SD Cards (with a capacity of at least 8GB) bootable by changing their default partition table to GUID using Mac OS X Disk Utility and formatting the card to use the Mac OS Extended file format, instead of standard FAT32 DOS formatting. Macworld’s Roman Loyola has posted a video tutorial showing how to create a bootable SD Card. Loyola also reports that a variety of other Macs, besides the SD Card equipped mid-2009 MacBook Pros, including an iMac and a Mac mini, can be successfully booted from SD Card boot disks via a SanDisk MicroMate SD card reader.

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