The SD Memory Card or Secure Digital Card was introduced in 2001 by SanDisk Corporation, Matsushita (Panasonic) and Toshiba. The SD Memory Card was based on the MultiMediaCard, MMC, memory card standard and has almost the same form factor, the size of a postage stamp, the only differences are that the SD memory card is slightly thicker and has a write protection switch. Since MMC cards are thinner than SD Memory Cards they can be used in all SD Memory Card slots but not vice versa.
The SD Memory Card is today the most commonly used memory card. It can be found in most digital cameras, PDAs and in many other electronic devices. The SD Memory Card slots can be used for more than flash memory cards. The SDIO, Secure Digital In & Out, is the general name for the many expansion modules that can be found in the SD Memory Card's form factor. SDIO modules can be inserted in the slot and be used for other functions like Bluetooth adapters, GPS receivers, digital cameras, TV tuners, etc.
The SD Memory Card was the first memory card to be introduced in the Secure Digital family, which today consists of three members. In 2003 the miniSD format, 60 % smaller than the SD Memory Card, was introduced as the second member in the Secure Digital family. In 2005 the microSD was introduced as the third and the smallest member in the Secure Digital family. miniSD and microSD often come with an adaptor so they can be used in full size SD Memory Card slots.
The official maximum capacity offered by the original SD format is 2GB. Although when some older devices were made it was not foreseen by the designers that SD cards would reach sizes of up to 2GB and therefore can only address a card upto 1GB, or even 512MB.
When buying a memory card it is important you check which card your device can accept, you should consider the format (e.g. SD), the size (e.g. 1GB) and speed (e.g. 133x). There are various compatibility checkers available, SanDisk and Transcend’s offer this service on their website.
You can use SanDisk's or Transcend’s compatibility checkers to see what specifications of card your device will accept, you don’t have to their card.
If you buy a card which is too big, a 2GB card for example, and your device was only designed to accept up to 1GB cards, it will either work although the 2GB card will appear as a 1GB card, or it won’t work at all, or it may appear to work fine until you realise half of the 50 photographs you took have disappeared. This is because your device’s filing system can’t manage the space on the card so it gets confused and loses them! The pictures will be there but not referenced correctly in the File Allocation Table (FAT).
This is not necessarily a faulty card but an incompatibility between card and device.
It should be the responsibility of the buyer to know what kind of card their device can accept. It is difficult for the seller to ascertain this as they do not own, use or have access to the device in question. The buyer can use compatibility checkers like the ones described above to check which kind of card they should buy, or refer to the instruction manual of their device or ask the manufacturer direct. It is a little like buying fuel for a car, it should be the responsibility of the driver of the car to know whether the car accepts petrol or diesel. The garage cashier cannot know as it is not their car. If the customer does buy the incorrect fuel would the garage be expected to take the fuel back and provide a refund or swap for the right fuel?
If a card is bought without checking it is the correct one for the device in question and indeed turns out to be incompatible it is not the sellers responsibility to accept the card back, after all the card is now second hand. The supplier/manufacturer will not take the item back unless it is faulty, therefore the original seller would have to sell the item as a used item, which always means at a loss.
However, if a memory card has not been opened and is like new it can be sold as such (not the case with fuel) and therefore can be accepted back as a return and exchanged for the correct item or a refund given. Because there were so many fake memory cards within the market a few years ago manufacturers started to make the packaging so it had to be destroyed to get to the card, i.e. packaging often has to be cut open with a sharp pair of scissors.
Therefore for a buyer not to check which card they need, to buy, open and use the card is not fair on the seller to then expect a refund if the card is found not to be faulty after testing in an appropriate device.
As mentioned earlier the maximum capacity of SD cards was 2GB but some card manufactures exceeded his limit and created 4GB cards which are not to the official SD specifications, so whether a 4GB SD card will work in your device becomes even more of a concern and using a compatibility checker and doing other research before buying is very important. On the flip side, it can be a helpful way of increasing the useful life of a non SDHC device.
What is SDHC?
To support the higher capacity needs, SD cards are now requiring a different design. The new SD 2.0 specifications - which officially supports from 4GB up to 32GB - is called Secure Digital High Capacity (SDHC). The SD Association defined 4 speed classes to help you identify speed and performance capabilities/minimum requirements of SDHC cards and their SDHC host products. Details on the SD 2.0 specification can be found on the SD association website (search SD Association).
Cards address data (read and write) at numerous speeds. Many factors impede this performance. SDHC guarantees a minimum read and write speed necessary to handle recording high quality video and audio. The maximum card speed may vary, but you can always depend on SDHC cards to meet your SDHC host product's high quality performance requirements.
Because SDHC works differently (supports the new higher capacity cards) this new card format is not backwards compatible with legacy SD format host devices. To avoid confusion the SD association stipulated to manufacturers using SDHC technology in their devices that the devices must have bare SDHC logo. Therefore when considering a new SD card check that your device shows the SDHC logo, if it does then you can purchase new SDHC card with confidence. If your device does not have a SDHC logo a SDHC card will not work, even though it will physically fit in the slot. The device will function as if it is a faulty card which is not the case.
Look at the SD association website for more details (search SD Association).