With an explosion of digital devices like cameras, camcorders, GPS receivers, PDAs, and video game consoles in the market, a need for storage devices arose, that could be small enough to be fitted inside them and have high storage capacities, coupled with high data transfer speeds.
The challenge was taken up by many leading consumer electronics companies and the 'Secure Digital (SD)' memory card was developed by SanDisk, Panasonic, and Toshiba. These are non-volatile type memory cards, that can store data, even when not supplied with power.
Though non-volatile data storage devices have been around for long, it is only recently that storage capacities in gigabytes, have been attained by memory cards. There are two main types. The first type is known by the name of SD card, while the other is known as an SDHC card.
Difference Between the Card Types
SDHC (Secure Digital High Capacity) cards, as their name suggests, are SD cards with higher capacities. They are named so, to distinguish them from the first generation cards, that were previously launched.
One thing that distinguishes SD cards from other storage formats like compact flash and USB flash memory devices, is that this technology is less open. In short, manufacturing companies have retained a proprietary hold over them. Both generations of SD cards are about the size of postage stamps.
One of the prime differences is with respect to storage capacity. SD cards that are first generation products of this technology, can offer a storage capacity, only up to 4 GB. In contrast, SDHC cards offer storage capacities up to 32 GB.
This makes them ideal for usage in digital camcorders, digital cameras, and other portable devices, as they require high storage capacities, as well as high data transfer rates.
One issue that often crops up with succeeding versions of any technology is backward compatibility. Newer version of a technology may or may not be fully backward-compatible. Any SD card is compatible with devices that are SD hosts, as well as devices built exclusively for hosting SDHC cards.
However, devices that conform to SD 1.0 and 1.1 specifications cannot be fitted with these cards. To conclude, SD cards work with SD host and SDHC based devices, but SDHC cards work only on SDHC host devices.
While SD cards are based on the FAT16 file type, SDHC cards work with FAT32 file format. However, support exists for other file formats like ext2, UFS2, and exFAT.
SDHC cards come in various classes, that are differentiated by the data transfer speeds (Class 2, Class 4, Class 6, Class 10), which they are capable of sustaining. The highest data transfer speed is offered by the Class 10 cards, which can provide data transfer at 10 MB per second. Higher the class, higher is the cost of the card.
You are advised to buy a SDHC card of an appropriate class, according to the data transfer rate allowed by your device. If you buy a higher class card, but the device you fit it in, cannot handle high data transfer rates, it would be a waste of money. Compared to SDHC, the SD cards are much slower in transferring data.
Opting for a SDHC card is the smart thing to do, for reasons that have already mentioned. A new breed of SDXC (Secure Digital Extended Capacity) cards is soon arriving, that will raise the overall storage capacity up to 2 terabytes, with transfer speeds reaching 2.4 gigabits per second.