The solution to this problem described and evaluated in this paper is Disk Cache. The idea is to buffer recently used portions of the disk address space in electronic storage. Empirically, it is shown that a large (e.g. 80% to 90%) fraction of all I/O requests are captured by a cache of reasonable (e.g. 8 Mbyte) size. This paper considers a number of design parameters for such a cache (called Cache Disk or Disk Cache), including those that can be examined experimentally (cache location, cache size, migration algorithms, block sizes, etc.) and others (access time, bandwidth, multipathing, technology, consistency, error recovery, etc.) for which we have no relevant data or experiments. We find that disk cache is a powerful means of extending the performance limits of high end computer systems.