A MicroSD aka TransFlash card on the left, Samsung's MMCMicro on the right
The smallest flash memory cards are so small that most users will find them hard to hold and handle. That's why they're not really designed for frequent changes or reuse. When regular access and handling is intended, conventional flash cards or USB pen drives make a better choice.
Multi Media Card Micro
With dimensions of 14 x 12 x 1.1 mm (0.55 x 0.47 x 0.04 in), Samsung's MMCmicro is a little bigger than a MicroSD card. But with these measurements, the word "bigger" is almost absurd. At the end of last year, Samsung announced these cards and promised 10 megabytes per second for reading, and 7 megabytes a second when writing to them. It's obvious that SLC flash lurks somewhere inside; for further proof, one need only consider its rated power levels of 3.3 or 1.8 V. Maximum capacity currently sits at a modest 256 MB, but that's sure to increase fairly soon.
Micro Secure Digital Aka TransFlash
With dimensions of only 15 x 11 x 1 mm (0.59 x 0.43 x 0.04 in), the MicroSD card is every bit as miniscule as the MMCmicro, and can even lay claim to the title of "smallest memory card in the world." SanDisk is taking over this format, which its original manufacturer brought to market under the TransFlash name. Likewise, MicroSD offers all the same features and functions as a conventional SD card, albeit with somewhat slower performance. But it's a great fit for even the tiniest of mobile phones, which won't feel too pinched by its capacity limits of 512 MB either. By year's end, SanDisk promises to hit the 1 GB mark.