Secure Digital
memory cards are lockable.
Consumers have a choice between Secure Digital (SD) and MultiMedia Card (MMC) technologies when purchasing flash memory cards for devices such as audio players or digital cameras. Currently, MMC cards are slightly outdated and SD cards are more popular.
Transfer
SD cards maintain an advantage with data transfer speeds up between 10 and 20 MB/s, while MMC memory cards can only read or write data up to 9 MB/s. While both cards had a similar transfer rate at one time, SD cards have seen improvements in transfer rate while MMC cards have not.
Capacity
SD cards have a larger range of data capacity than MMC cards, which can only store 32GB of data. In contrast, SD memory cards are available with capacities of up to 2 TB. 1, 2, 4 and 8GB capacities are common with SD memory cards.
Write Protection
SD memory cards have a security feature known as write protection. When the card owner moves a switch on the card into the correct position, the card becomes locked and data cannot become lost or erased until the owner unlocks the memory card. MMC memory cards do not offer this feature.
Physical Appearance
SD cards are slightly larger than MMc cards, to prevent insertion into MMC slots. The dimensions of an SD card are 32 mm by 24 mm by 2.1 mm, while the dimensions of an MMC memory card are 24mm by 32 mm by 1.4mm.
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