Storing data forever is impossible at the moment, as storage methods eventually expire. You might be able to play an old CD but you won't be able to do this endlessly. Hitachi might have found the solution in their most recent invention; a glass disk which should be able to hold data forever.
The magic in Hitachi's invention comes from how data is stored on the glass. Binary dots are written to the glass, and can be read using a common microscope. The idea behind this is that future technologies won't leave this medium behind, like they did with the floppy disk.
The way in which this works is impressively simple, being similar to how records are read. If you have a computer with the right software and an optical microscope hooked up to it, it should be possible to simply feed the data into the computer. Currently the size of the data that can be stored isn't known, but Hitachi plans to increase it for the future.
The glass used is specifically quartz glass, meaning there is some silicon in an amorphous manner. Measuring only two centimetres square and two millimetres in thickness, you don't want to lose one of these.