Difference Between SD and MMC

SD vs. MMC

Secure Digital (also known as SD) is a memory card for the use in portable devices (such as digital cameras and MP3 players). It was developed by SanDisk, Panasonic and Toshiba. Most standard SD cards have a wide range of storage capacities (ranging from 152 MB to 2 GB). High capacity SD cards (or SDHC) can hold incredible amounts of data, ranging from 4 GB to 32 GB. As of 2009, the newest permutation of the SD card, the eXtended Capacity SD card (SDXC), can hold up to 2 TB (that is terabytes) of information.

The MutliMediaCard (also known as MMC) is a standard flash memory card, which is to say it is the prototype of the memory card as it is today. Developed by Siemens SG and SanDisk, its design is loosely based on Toshiba’s NAND-based flash memory (a flash memory that consists of blocks that are made up of a certain amount of pages, ranging from 512 to 4096 bytes in size). Most MMC cards have a capacity ranging from 152 MB to 32 GB.

While SD cards are based on the MMC format, the two are virtually dissimilar in appearance. SD cards were created asymmetrically in order to avoid insertion in the wrong direction. They are also thicker than MMC cards, with dimensions usually ranging around 32 mm x 24 mm x 2.1 mm. Most MMC cards have dimensions ranging around 24 mm x 32 mm x 1.4 mm. As for the electronic make-up of the SD card, it differs significantly from the MMC. The SD card’s electrical contacts are hidden securely underneath the surface of the card. This, of course, protects them from physical contact with the fingers of the one using the card (thus limiting the risk of damaging the card’s contents). The transfer rates are also a bit faster than those of standard MMC cards (whose transfer rate is usually around four, or at times, eight bits at a time). SD cards can transfer items at a rate of 10 – 20 MB per second.

There are several variants of the standard MMC. The Reduced-Size MMC (RS-MMC) is about half the size of a standard MMC, and can be used in SD sized slots in portable devices. The SD also comes in the form of the MiniSD; however, it cannot fit in MMC sized slots.

Summary:

1. SD cards now have a holding capacity of up to 4 TB; MMC cards have a maximum holding capacity of 32 MB.

2. SD card dimensions are usually 32 mm x 24 mm x 2.1 mm; MMC card dimensions are usually 24mm x 32 mm x 1.4mm.

3. SD cards have a transfer rate of about 10 – 20 MB per second; MMC cards have a transfer of up to 8 MB per second.

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