Flash memory is a kind of semiconductor-based, non-volatile, rewritable computer memory; that is, it has many of the same characteristics as RAM, except that the data is not wiped out when the machine is turned off. Flash memory stores bits of data in memory cells, but the data remains saved even when electrical power is cut.
Due to its higher speed, durability, and low energy consumption, flash memory is ideal for many applications, such as digital cameras, mobile phones, printers, PDAs, laptop computers, and device that can record and play back sound, such as mp3 players. What's more, this kind of memory has no moving parts, which makes it very shock-resistant.
There are many competing, incompatible memory card formats, almost one for every manufacturer. Among these formats of memory cards, the most common are
|Dimensions (mm)||Volume (mm3)||Weight (g)||# of connectors||Transfer rate||Theoretical capacity||Theoretical size|
|Compact Flash type I||43 x 36 x 3,3||5 108||3,3||50||20 MB/s||137 GB||128 GB|
|Compact Flash type II||43 x 36 x 5||7 740||4||50||20 MB/s||137 GB||12 GB|
|SmartMedia||37 x 45 x 0,8||1 265||2||22||2 MB/s||128 MB||128 MB|
|MMC||24 x 32 x 1,4||1 075||1,3||7||20 MB/s||128 GB||8 GB|
|MMC Plus||24 x 32 x 1,4||1 075||1,3||7||52 MB/s||128 GB||4 GB|
|RS-MMC MMC Mobile||24 x 16 x 1,4||538||1,3||13||8 MB/s||128 GB||2 GB|
|MMC Micro||14 x 12 x 1,1||185||< 1||13||128 GB||2 GB|
|Memory Stick Standard, Pro||21,5 x 50 x 2,8||3 010||4||10||2 MB/s||128 MB||128 MB|
|Memory Stick Duo, Pro Duo||20 x 31 x 1,6||992||2||10||20 MB/s||32 GB||16 GB|
|Memory Stick Pro-HG||20 x 31 x 1,6||992||2||10||60 MB/s||32 GB||32 GB|
|Memory Stick Micro M2||12,5 x 15 x 1,2||225||2||10||20 MB/s||32 GB||8 GB|
|SD||24 x 32 x 2,1||1 613||2||9||20 MB/s||32 GB||32 GB|
|mini SD||20 x 21,5 x 1,4||602||1||11||12 MB/s||32 GB||4 GB|
|micro SD||15 x 11 x 1||165||0,3||8||10 MB/s||32 GB||12 GB|
|xD||25 x 20 x 1,8||890||2,8||18||9 MB/s||8 GB||2 GB|
It should be noted that there are multi-format memory card readers, most of which can be plugged into a USB port.