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