So if you've got some data you want to store between runs of a program (or a set of programs), you need to write it to disk somewhere. To get it back you need to read it from disk and that means knowing what format it is in, i.e. knowing how it was written to disk. Often you are adding a program to a suite of existing software and the file formats have already been determined, e.g. think of the weather data file we worked with in CPSC 128. Sometimes though you are in at the beginning of a project and get to decide how to write the data to disk. In this case your task is to design a file format, i.e. to decide how the relevant information should be written to disk. Generally we'd like a way that is easy to code, both for reading and writing, and that is compact and thus efficient in its use of disk space. Perhaps surprisingly quite different approaches can usually be taken to storing data on disk. One accessible problem that affords different alternatives is the problem of storing the state of the universe in Conway's Game of Life so in this unit we'll consider alternative ways of storing and restoring a Life universe to and from disk.