Released in 2006, the Pentax Optio M20 digital camera comes with 22MB of built-in memory, but also features a built-in Secure Digital, or SD, card slot for expanded memory. The camera supports standard SD and high-capacity SD, or SDHC, memory cards, which offer different amounts of memory.
Types
Before identifying the amounts of memory afforded by SD and SDHC memory cards, it's best to first understand the different card categories that are available. As of June 2011 the SD and SDHC card categories include standard-, mini- and micro-sized versions. A third category, known as extra-capacity SD, or SDXC, is available only in standard-sized SDXC and microSDXC versions. Identifying the correct size of SD or SDHC card to use in the Optio M20 shouldn't be a problem, as long as you keep in mind that these cards are the largest SD cards available.
Dimensions
To further clarify the differences between the different sizes of SD cards available, it's helpful to familiarize yourself with the different card dimensions. SD, SDHC---the ones used in the Pentax Optio M20---and SDXC cards are about the size of a postage stamp, measuring .9 inches wide, 1.3 inches long and .08 inches deep, and weighing .07 ounces. MiniSD and miniSDHC cards are about 37 percent of the size of the standard-sized SD cards, measuring .8 inches wide, .8 inches long and .06 inches deep, and weighing .03 ounces. At .02 ounces, microSD, microSDHC and microSDXC cards are about the size of a fingernail, measuring .4 inches wide, .6 inches long and .04 inches deep.
Capacities
Deciding which SD card capacity is right for you depends on your needs. An SD card will provide you with up to 2GB of added memory, while an SDHC offers between 2GB and 32GB of memory. The Pentax Optio M20 is a seven-megapixel camera that also records video at 30 frames per second at up to 640 by 480 pixels of resolution. If you plan to use the camera for still photography only, an SD card will likely suffice. However, if you intend to use the Optio M20 to record video or store a large number of still photographs, you will probably find an SDHC card more appropriate. As a side note, SDXC and microSDXC provide between 32GB and 2TB of memory and are designed mainly for large-format, high-density video recording.
Speeds
With regard to video recording, which is offered by the Pentax Optio M20, all SD cards, including SD and SDHC, fall into two categories: Speed Class and Ultra-High Speed Class. The SC class is subdivided into four speed classes---Classes 2, 4, 6 and 10---that are compatible with normal or high-speed bus interfaces. Normal-speed interfacing, as provided by the Optio M20, is compatible with the SC's Classes 2, 4 and 6. Class 10 is intended to facilitate high-definition video recording, which is offered by newer and high-end digital cameras.
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