Abstract: A disc file system is described in which the disc space is divided into very large blocks of at least 64k bytes. A large file is allocated a whole number of these large blocks, contiguously where possible. Small files reside in small file areas each of which is composed of a number of large blocks. Space in these small file areas is allocated in multiples of a small block size (e.g. 4K bytes). The use of large and small blocks reduces the wastage of space that would occur if small files were written into large blocks. The amount of head movement when reading large amounts of data from large files is reduced because of the large block size and because the large blocks are allocated contiguously.