* Average file size using cameras highest resolution JPEG mode. Actual number of photos, songs, and minutes will vary depending on camera/device model, format resolution and compression, usable capacity, and bundled software. Actual usable memory capacity may vary. 1MB equals 1 million bytes; 1GB equals 1 billion bytes.

NUMBER OF IMAGES STORED ON A DIGITAL CARD
The number of pictures you can take varies depending on your camera model and complexity of the scene being photographed. To calculate how many pictures your card can hold, divide the capacity of your card by the average file size of your images. For example, if you have a 256MB card, and use a camera that has an average file size of 1.2MB, then 256 divided by 1.2 gives you approximately 213 pictures. As you change modes on your camera, the number of images will increase if you shoot in a lower resolution mode, and decrease if you shoot in a higher resolution mode.

Secure Digital (SD) is a flash (non-volatile) memory card format developed by Matsushita, SanDisk, and Toshiba for use in portable devices. Today it is widely used in digital cameras, handheld computers, PDAs, mobile phones, GPS receivers, and video game consoles. Standard SD card capacities range from 8 MB to 4 GB and for high capacity SDHC cards 8 MB to 32 GB as of 2008.

Like other flash card technologies, most SD cards ship preformatted with the FAT or FAT 32 file systems. This file system allows the card to be accessed on virtually any host device with an SD reader. Also, standard maintenance utilities can be used to repair or retrieve corrupted data. However, because the card appears as a removable hard drive to the host system, the card can be reformatted on almost any supported by the operating system.

There are different speed grades available for SD & SDHC cards, measured with the same standard as Optical Drives (in multiples of 150 kB/s - 1x = 150 kB/s). Basic cards transfer data up to 6x. High-speed cards are made with higher data transfer rates like 66x (10 MB/s), and high-end cards have speeds of 150x or higher. Note that maximum read speed and maximum write speed may be different, with maximum write speed typically lower than maximum read speed. Some digital cameras require high-speed cards (write speed) to record video smoothly or capture multiple still photographs in rapid succession. The SD card specification 1.01 allows for a maximum speed of 66x. Higher speeds of up to 150x are defined by specification 1.1.

It is worth noting that defragmenting an SD provides no performance advantage, since flash memory is truly random-access (unlike a hard drive), so there is no performance gain.

The SD format has proven to be very popular. However, the higher capacity SDHC cards, are not compatible with standard SD card reading devices. Since SDHC format cards have the same physical shape and form factor as the standard SD format, care should be taken to avoid confusion for consumers. SDHC cards require an SDHC capable device firmware, generally not found with older devices.