A lot of attention after the recent launch of Windows Phone 7 by Microsoft has surrounded the issue of expandable storage, and the way microSD cards are used in the device. Today, Engadget came across the full story behind what happens to a memory card once formatted for the phone, and why it becomes unusable in other devices once removed.
In designing the WP7 platform, Microsoft never intended for OEMs to ship devices that expose removable storage to the end user. Many OEMs use memory cards, rather than soldered-on chips to allow them to easily and flexibly create a variety of SKUs with different levels of memory, the official line was that such cards should be glued into place. At some point in the process, this message was forgotten by a number of device makers, and handsets such as the Samsung Focus are being marketed with fully-accessible memory card ports.
What many people forget is the fact that the "S" in "SD" stands for "Secure". Windows Phone 7 is one of a very small number of platforms which actually makes use of these features. The reason that a card, once formatted in a WP7 device, becomes unusable in other devices, is that after the format, a random password is generated, which is then required to read from and write to the card. This is stored on the internal memory of the phone, and not known to other devices. Without the password, the data stored on the card is unusable to other devices, and the only operation they can perform is a fresh format.
Engadget discovered that the Symbian platform is one of the few others which implement the additional security features used by WP7, and have successfully used a Nokia N8 to erase a microSD card that had been used in a WP7 device, and restore it to a workable condition. This means that placing a memory card into your new handset does not mark the end of its usefulness outside of that device, as many reports have claimed, so long as you can get your hands on another device which supports the security features, and is able to perform an erase on the card.