Secure Digital (SD) format is used by all major digital memory manufacturing companies of the world including giants like Sony and Siemens. SD cards are available in various memory capacities, sizes and data transfer speeds. The maximum size of the cards is that of SD or SD HC cards and the smaller ones require an adapter that scales them exactly to the size of a standard SD card.While most modern Laptops come with inbuilt SD card readers, devices that have only USB inputs require some kind of reading device to access or modify the data in the cards. SD card readers solve this purpose. SD card can be inserted inside the card slot in the readers which have a USB interface to connect to the desktop.