Memory cards - an overview
Flash memory cards are an essential part of the imaging process, as they record and store the precious images taken. These cards are solid state storage devices that do not contain any moving parts and are well suited for use in digital cameras due to their reliability and compact size. Several different types of memory cards for use in digital cameras have been released over time. The most prevalent types used for digital imaging are compact flash (CF) and secure digital cards (SD, SDHC, SDXC), while others, such as the Memory Stick or the xD card, are promoted by particular camera manufacturers.
Despite having been around since 1994, the relatively bulky CF cards have preserved a prominent place in the photographers' bag, as they have proven rugged in use and have offered very good capacity and speed performance at a reasonable price. There are two types of CF-cards available that share the same electrical interface, but differ by width: the thinner type-I can fit into the socket of the thicker type-II, but not vice versa. Virtually all CF-cards used in digital cameras nowadays are of type-I.
Secure Digital cards also come in different varieties. The original SD card had a storage capacity of up to 2GB. The subsequent SDHC (secure digital high capacity) and SDXC (secure digital extended capacity) versions increased the maximum storage capacity to, respectively, 32 GB and 2048 GB. SD cards (and even more so micro SD cards) have a clear size advantage over CF memory and dominate in use for small interchangeable lens cameras and compact cameras. Indeed, over time the development in memory cards has clearly shifted to more and more compact types of flash memory, while offering increased speed and storage capacity.
|Headline specifications of different memory cards|
|Memory card type||Abbreviation||Write Speed|
|Compact Flash, type I||CF-I||150||256||42.8 x 36.4 x 3.3||12||1994||Advanced DSLR|
|Compact Flash, type II||CF-II||16||8||42.8 x 36.4 x 5.0||15||1994||Advanced DSLR|
|Extreme Digital Picture Card||xD||4||2||20 x 25 x 1.7||2||2002||Fujifilm/Olympus|
|Memory Stick Pro||MS Pro||20||4||50 x 21.5 x 2.8||4||1998||Sony digicams|
|Memory Stick Pro Duo||MS Pro Duo||20||32||31 x 20 x 1.6||2||2003||Sony digicams|
|Micro Secure Digital||micro SD||6||4||11 x 15 x 1||0.4||2004||Compact cameras|
|Micro Secure Digital High Capacity||micro SDHC||10||32||11 x 15 x 1||0.4||2007||Compact cameras|
|Secure Digital||SD||20||2||32 x 24 x 2.1||2||1999||Compact cameras|
|Secure Digital High Capacity||SDHC||95||32||32 x 24 x 2.1||2||2004||Digital cameras|
|Secure Digital Extended Capacity||SDXC||280||512||32 x 24 x 2.1||2||2009||Digital cameras|
|XQD card||XQD||168||64||25 x 20 x 1.78||10||2012||Advanced DSLR|
Below is a list of memory card issues or questions that photographers have encountered. Hopefully, the respective comments or responses will prove helpful. Please send me a note, if you know of any other tips or tricks that should be added to the list.
Memory card FAQ
What are SD Speed Classes?
Speed classes are standards that regulate the minimum data transfer in SD, SDHC, and SDXC memory cards. The ratings make it possible to compare the speed performance of memory cards.
What does UHS stand for?
UHS (Ultra High Speed) represents the fastest performance category for SD cards, defined by a bus-interface speeds up to 312 Megabytes per second.
Can one save data from taking both still pictures and video on a single memory card?
Yes, mixing data from stills and video does not cause any problem, as long as the card has sufficient capacity.
Flash memory is very durable, so that CF and SD cards can last for 50 years or more. However, technical progress might limit the economic shelf life of a particular storage device.
Is it better to format a memory card inside a camera or with a computer and card reader?
Both methods clean out all files and set up the memory card for use. However, in-camera formatting is generally recommended for obtaining a file system that is optimized for the particular camera.
Can images that have been deleted be retrieved from a memory card?
Recovering deleted images might be possible with special software that card manufacturers have been making available. Respective software-tools can be found on the manufacturers' websites [lexar.com].
Are memory cards dust- and splashproof?
No, memory cards should generally not be exposed to dirt and water. However, some manufacturers have produced special high durability cards. For example, SanDisk advertises that its Extreme Pro range of SDHC cards is water proof, temperature proof, shock and vibration proof, as well as x-ray and magnet proof [sandisk.com].
Even though memory cards are generally quite durable, following some basic handling guidelines will ensure that the flash storage devices will provide valuable services well into the future. One piece of good practice is to format one's card in regular intervals in order to reduce data errors and maintain the rated capacity and speed of the storage device. Other tips to keep your card well can be found, for example, at slrlounge.com.