Apple’s newly-released 13″ and 15″ MacBook Pro notebooks now boast a feature in which users can boot from the SD card slot in a pinch.
According to a tech note published by Apple, users can install Mac OS X on an SD card and use it as a startup volume simply by changing the default partition table to GUID using Disk Utility, and then formating the card to use the Mac OS Extended file format.
This capability can be particularly useful in the event that you run into problems with a MacBook Pro’s built-in storage options, particularly those equipped with traditional hard disk drives, which include moving parts.
The company notes that the new MacBook Pros have a maximum speed of 240 Mbit/s for SD media using the SD card slot, which easily exceeds the transfer rate of most SD media. For example, Class 2 media has a maximum transfer rate of 4 Mbit/s; Class 4 media has a maximum transfer rate of 4.8 Mbit/s; and Class 6 media has a maximum transfer rate of 45 Mbit/s.
SD cards that conform to the SD 1.x and 2.x standards should work in the slots, though they also accept cards that are Standard SD (4 MB to 4 GB) and SDHC (4 GB to 32 GB). MultiMediaCards (MMC) can also be used, as well as MiniSD, MicroSD, and higher density formats like MiniSDHC and MicroSDHC, assuming they’re first inserted into one of the “passive” adapters on the market that conform to the width and thickness specifications for the slot.
Although the SD card specification for a memory card is 32mm x 24mm x 2.1 mm, Apple says you can also use thinner cards, such as the aforementioned MMCs. Cards that have a thickness greater than 2.1mm or that have surfaces that exceed 2.1mm, should not be used, the company warns, as they may damage the SD card slot if inserted.
The slots also accept cards that exceed 32 GB, but as Apple notes, most media manufactures preformat their media using common block-and-cluster sizes that do not approach the theoretical limits of a given file system.
Most SD cards use the FAT32 file format which is commonly available up to a capacity of 32 GB. Some smaller capacity cards use the FAT16 file format, which is generally available in capacities of up to only 2 GB.
SD cards that use the exFAT file system are not supported, nor are SDIO (Secure Digital Input Output) cards.