How to Choose the Right SD Memory

I wanted to buy some new memory for my cell phone the other day. I went to the shelf where they had all the SD cards and I figured I would just grab one to be done with it. As I put my hand on the 8GB package, I noticed it said SDHC. I immediately wondered if this was the right kind of SD card for my device. I asked the salesperson what the difference was. He offered nothing, and so I left to go do some research. Here is what I found.

Some people think that SD means SanDisk but it doesn't. SD stands for Secure Digital. There are different sizes of the SD card. There are also different speeds of SD cards. Each card has a rating that indicates the speed. The rating is based on either write speed or read speed depending on the company. This causes confusion. The speed is the same standard by which CDROM drives are measured. Here is a chart that describes the speeds.

Rating / Write Speed MB (per second) / SD Class
6x / 0.9 / n/a
10x / 1.5 / n/a
13x / 2.0 / 2
26x / 4.0 / 4
32x / 4.8 / 5
40x / 6.0 / 6
66x / 10.0 / 10
100x / 15.0 / 15
133x / 20.0 / 20
150x / 22.5 / 22
200x / 30.0 / 30
266x / 40.0 / 40
300x / 45.0 / 45

Remember that each card can have a different rating, and it has nothing to do with the physical size or capacity.

Here is the run down of the different sizes, in terms of both physical and capacity.

SD 1999 Small (32 mm × 24 mm × 2.1 mm), holds up to 2 GB
miniSD 2003 Compact size (21.5 mm x 20 mm x 1.4 mm), holds up to 2 GB
microSD 2005 Sub compact size (11 mm x 15 mm x 1 mm), holds up to 4 GB
SDHC 2006 Physically the same as SD, holds up to 64 GB
miniSDHC 2007 Physically the same as miniSD, holds up to 32 GB
microSDHC 2007 Physically the same as microSD, holds up to 32 GB
SDXC 2009 Announced at CES 2009, due in 2010, holds up to 2 TB

As you can see there are 3 different physical sizes (Regular, medium, and large). There are also various degrees of capacity depending on which generation. The new SDXC specification will hold up to 2 Terrabytes of information.

Now in order to make sure you get the correct SD card for your device, it is important to read the documentation carefully. Some devices do not support SDHC. If it says supports up to 2GB, then it is most likely that only a standard SD memory card will work in the device. If you are unsure, the best bet is to buy a standard SD memory and it will work because any device should be backward compatible.