SD Memory Card Types

Secure Digital (SD) & Secure Digital High Capacity (SDHC)

The postage stamp size Secure Digital (SD) card is the most popular type of memory card on the market. Its small size, large capacity and robust design has made it common in everything from cameras to MP3 players. Other advantages include relatively high speed data transfer, a mechanical write protect switch to protect data and built-in copyright protection technology.

miniSD

miniSD cards use the same technology as SD cards, meaning users get all of the advantages of an SD but in a smaller package. These smaller SD cards are used in smaller devices such as mobile phones and MP3 players. miniSD cards are usually sold with an adaptor which allows you to use the card in a normal SD slot.

microSD

An even smaller SD variant, the microSD format is currently most popular with mobile phone manufacturers due to its extremely small size. They're almost too small to comfortably hold and swap in and out of devices.

Like SD and miniSD cards, microSD cards are ideal for storing media-rich files such as music, videos, and high-resolution images. microSDHC cards offer even more storage (Above 2GB) for everything needed in the mobile world while keeping the same physical specifications as standard microSD cards.

Although mainly used with mobile handsets the microSD card is also supported natively in a variety of handheld GPS devices, portable audio players, video game consoles and expandable USB flash memory drives.

The miniSD card was developed to meet industry demands for downsizing mobile phones. It is only 37% the volume of an SD Memory Card. Despite its tiny size, the miniSD card offers all the benefits of the original SD Memory Card, including copyright protection. By inserting the miniSD card into the miniSD adapter, you can share a variety of digital data among standard SD-enabled products. 

Dimensions

Note that a memory card's dimensions are determined while holding the card with contact pins facing up. Horizontal measurement is width, vertical measurement is length, depth is thickness. For most cards length is larger than width, although this is not always the case. Also, most cards include a direction arrow to aid insertion; such an arrow should also be facing "up".

Speed Rating

The SD Card Association (SDA) has established a new specification rating the minimum data transfer for both SD/SDHC Memory Cards and SD/SDHC host products.

With the new Speed Class specifications, the host product can check the fragmented state in the card and calculate the write speed in each part of the card. The host can then determine where to write the data according to its speed requirement.

What is Fragmented State?

The memory area of a card is divided into minimum memory units. The host product writes data onto those memory units where no data is occupied. The fragmented state reflects how these memory units are occupied. The write speed depends on this state.

The SDA has specified operating conditions for SDHC Memory Cards thatguarantee the minimum speed according to the card's speed class. Class logos are used to identify cards that comply with these specifications.

The Class logos must appear near the card's logo on all SDHC Memory Cards (above 2GB).

SD Speed Class logo is optional for SD Memory Cards (2GB and less).

The following speed classes have been established: