The details of how data is stored on cassette will be covered later. This section just describes the general format of a file on tape as it appears to the user.
A file consists of a header chunk, followed by one or more data chunks. Each chunk will be preceded by necessary information for synchronising the tape reading routine and establishing the speed, including a long leader tone. Details of this are given later.
The header chunk does not contain any data from the file. It contains the filename (which may be null), and a protection flag which can be used to prevent simple tape to tape copying (see later). The header chunk is used to identify the file.
Each data chunk contains exactly 4K of data from the file, except for the last one which may have any amount from zero bytes up to 4K. This smaller chunk is used to mark the end of the file. The data within each chunk is split up into 256 byte blocks, with a CRC check done on each block. This ensures that a bad chunk will be rejected fairly quickly.