All You Ever Needed to Know About SD Cards
The Secure Digital Memory Card (SD Card) started life in 1999 when three major corporations Matsushita, Toshiba and Sandisk begun to develop the secure digital memory card. The devices are used in many products such as mobile phones,cameras,hand held computers notebooks and media players.The design is an non volatile memory its size 32mm,24mm by 2.1mm which gave DRM approximately SDMI and for that time a larger memory. - sdhc card
The Sony Memory Stick was developed the year before so the SD card was designed to take on the stick. The design was based on the Multi Media Card format but with differences.
In order to insert the correct way the card has asymmetrically shape. SD cards at 2.1mm are thicker than the MMC at 1.4mm. Recessed underneath the surface are the electrical contacts put this way as not to touch the operators fingers.
Transfer rates are in the 10-20 mbs range though development that would change.
Devices that used MMC won't take SD cards in reverse MMC will go into devices using SD.
The file system within the SD card is formatted with either FAT16 for cards with 4 GB or fewer and for cards 4 GB and above they can be only be used by data system that supports the grater storage size like FAT32 which can be positioned on top of the MBR partition scheme.Applying this system will allow access with the card to any host using a SD card reader.
SD cards possess a write protection tab around the left side when the tab is present then your card cannot be written to if the tab is closed the card can be written to. Some of the other SD family just like the micro or mini SD cards would not have write protect tabs. Devices by using this format request a 128-bit identification string,12 bits are used in the memory clusters which are in the range of 1 to 4096, 3 bits are employed to identify the block cluster that when decoded could read 4,8,16,32,64,128,256,512.blocks.
Speed ratings with the SD cards are:
class 2 16 MBit-s (2 mbyte-s)
class 4 32 MBit-s (4 mbyte-s)
class 6 48 MBit-s (6 mbyte-s)
Fragmentation of your Secure Digital card just isn't ideal because it will degrade the card limited to the amount of writes before the card may fail is 100,000 times.
In 2000 the SD Association was formed from the three corporations Matsushita, SanDisk and Toshiba and the SD is now under the control of the association. They now define 1 GB cards and 2 GB cards specifications and there design.The SD specification can also be covered by patents like US patent 5602987. - sdhc card