Unless you have been hiding in a hole somewhere, you probably already know that SD cards are now the most popular memory cards for cameras, PDAs and Smart Phones. It is also likely that you share some confusion with the rest of the consumers of these cards about the differences between SD, miniSD and microSD. On top of that confusion, you also have to deal with SD versus SDHC cards and the various speed ratings for these cards; like 12X, 150X, Class 4 and Class 6.

Card Size

SD cards are the larger of the cards and are typically used in cameras and portable GPS devices. The miniSD cards are the mid sized cards. These were mostly used in PDAs and various Smart Phones. Recently the PDA and Smart Phone market has moved to using the microSD cards. Since the phones and PDAs have shrunk in size, so have the memory cards for these devices.

Most computer stores and camera stores now sell adapters that allow you to use the smaller cards in devices that take the larger cards. This is useful for transferring data from a micro or miniSD into a computer that only has an SD reader.

The image above on the right shows the comparative size of these memory cards. (The image comes from Wikipedia’s site via the GNU Free Documentation License.)

Memory Capacity

The “HC” that is appended at the end of a card name stands for High Capacity. The capacity limit of non-HC cards is 4 GB. HC cards start at 4 GB and have a specified limit of 32 GB although theoretically larger capacities are possible. However, most devices have limits that are far smaller than that. For example, a Smart Phone that I purchased recently has an upper limit of 8 GB for microSDHC cards.

Speed Ratings

The 12x, 150X, various multiples in between, and Class ratings refer to the transfer speed of the cards. The number preceding the X is multiplied times 150 KBs. This usually refers to the highest speed that you can read data from the card. Writing to the card is usually slower. Faster write speeds are required by cameras that record video or take pictures with more megapixels.

The Class ratings refer to the transfer speed for HC cards. The number following the Class refers to the MBs that the card transfers. The three numbers that are used at this time are 2, 4 and 6.

Conclusion

Hopefully this has made it a little easier for you to decide which card to buy. Just remember to read the user’s manual of the device that you purchased and buy a card with the right size, capacity and speed for that device.