Service mark symbol. The service mark symbol (â ), the letters SM in superscript style) is a symbol used in the United States to provide notice that the preceding mark is a service mark.
Size matters: The micro and mini USB connectors are of similar width. But the micro connector is much thinner (smaller vertical dimension). Some product designs were not able to accommodate the height of the mini receptacle and the new thinner receptacle will encourage and allow thinner products.
This resulted in the miniSD format, measuring 21.5 x 20mm, and then microSD cards, measuring 11 x 15mm. You can use a miniSD or microSD card in an SD card slot by plugging it into an SD-sized adapter, and some mini/micro cards are sold with them. Obviously, you can't fit an SD card into a miniSD or microSD slot. I assumed most of us needed different sizes, so it's handy if all your devices use the microSD format.