Hardware Reference
In-Depth Information
The higher the speed class number, the faster the card can transfer data.
Table 10.3
lists the speed-class recommendations for different types of still photo and video
recording tasks.
Table 10.3. Recommended Speed Classes for Photo and Video Uses
As you can see from
Table 10.3
, speed-class ratings are a useful guide to selecting suitable cards for
use with video recording. However, continuous shooting in still photography is more heavily
influenced by maximum card and bus speed. Thus, many vendors of SDHC cards also provide their
own maximum speed ratings.
Note
For more information about vendor speed ratings, such as 133X, and how they correspond to
speed-class ratings, see this Lexar white paper (PDF format) on “Understanding SD
Association Speed Ratings” (available from
SDHC and SDXC cards might also be labeled with a different marking, the Ultra High Speed (UHS)
Class marking. This mark resembles a stylized U with a number inside. U1 indicates a card has a
maximum speed of 104MBps. All cards with a UHS class 1 marking are also Class 10 compliant.
File Systems Used by Flash Memory
USB flash memory drives typically use the FAT32 file system, which supports up to 2TB of capacity.
Flash memory cards up to 2GB in size use the FAT16 file system, while SDHC and Compact Flash
memory cards with capacities above 2GB use FAT32. SDXC cards have capacities larger than 32GB
and use the Microsoft-developed exFAT file system.
To learn more about FAT16 and FAT32, see
Chapter 9
.
SDXC cards typically use the exFAT (FAT64) file system. exFAT uses a 64-bit address table to
support capacities of up to 512TB (recommended) and 64ZB (maximum size). FAT64 is designed
specifically for use with flash memory, is optimized for movie recording, and supports universal time
coordinate (UTC) time stamps.
Windows Vista SP1, Windows 7 SP1, and newer include built-in support for SDXC. To add support
for SDXC to older versions of Windows, see
http://support.microsoft.com/kb/955704
and see the
service pack requirements.
