Algorithm 891: A Fortran virtual memory system. Fortran_Virtual_Memory is a Fortran 95 package that provides facilities for reading from and writing to direct-access files. A buffer is used to avoid actual input/output operations whenever possible. The data may be spread over many files and for very large data sets these may be held on more than one device. We describe the design of Fortran_Virtual_Memory and comment on its use within an out-of-core sparse direct solver.