Own a Mac?
Ever stuck a multiple gb SD card into your camera/phone/pc only to have it report 200mb/card unrecognizable? and that is, no matter how many times you try to format it in Windows or Mac? Even checked Disk Management under My Computer> Manage or Disk Utility and tried formatting the disk as DOS FAT?
This is one annoying problem and only (i think) happens when you format the SD card with a Mac. OSX leaves a 200mb partition on the card which gets recognised and mistaken as the main partition on anything BUT a Mac. While conventional tools and methods (format, erase etc) cannot reverse this, there is one very useful tool that can help with this specific issue, made by SD association. The rest is quite simple really, just grab the tool called SD Formatter and format away.
And now you have your 4gb or whatever back.