Here are the few snippets of info I know about black boxes : They are actually bright orange - this helps crash investigators find them! They also have transmitters in them to aid their location. They are placed to the rear of the plan as this is the part of the plane that will suffer least damage in a forward moving collision. They record both the cockpit voices and flight data, such as altitude, speed, direction etc. They are made in a way to maximise their chances of surviving a crash - the medium on to which data is recorded (either tape or, in more modern recorders, memory chips) is contained in a water, fire and impact-resistant casing.

In addition to the points made before the data storage chips are coated in a jelly that makes them mouch more shock and fire resistant. Also, the way data is written is very important. Modern "Black boxes" record the data in such a way that even if some of the chips are destroyed, the information for a particular time sequence is not completely destroyed. Think of it like this - normally, each data storage chip would be a separate "chapter" of the flight. Hence, if a chip was damaged or destroyed, then the entire chapter would be lost. Nowadays consider the "sentences" are stored on different chips, i.e. sentence 1 is stored on chip 1 etc, till the number of chips runs out, and the next sentence is written to chip 1 again. This means that if any of the data chips are destroyed, the chances are that the sequence of events before and after the events on that chip are still decipherable, hence the events can be reconstructed with quite some accuracy.