The type of memory you are asking about is called “Non-volatile” memory – it doesn’t need a power source to keep the information. Almost all non-volatile memory that we use these days in USB sticks or camera memory cards is based on a technology called floating-gate transistors.
There are different types, but they work in roughly the same way. When you apply a high voltage, it is enough to push or pull electrons into a small part of the memory (equivalent to a 0 or a 1). Those electrons will stay there for a long time (months or years, but not forever). Using lower voltages, you can read whether the part of memory is full of electrons or not.
You can look up “floating-gate transistors” for more information, but you’ll probably need to read about how a standard MOSFET transistor works in order to understand what you are reading.
Hi crunchiejelly!! Drew is spot on! All that information you put on that USB stick is encoded with the positions of tiny electrons! The USB is set up so that those electrons can be in one of two spots like the flip of a switch. We label those as ‘0’ or ‘1’. This is a what is called a “bit” of information! Our computers get the information off our flash drives by reading out strings of these 0’s and 1’s. We have all kinds of clever coding schemes for how this information read out occurs! The most common is the ASCII code which translates specific sequences of 0’s and 1’s to letters – check out the binary to ascii to spell wikipedia – http://en.wikipedia.org/wiki/Binary_code – its pretty neat!!
To me its just so crazy all that information can be written in electron positions! I put a picture on my flash drive, it is read into a bunch of zeros and ones, and my computer can read those out later. Really AMAZING!