A reimplementation of the UNIX TM file system is described.The reimplementation provides substantially higher throughput rates by using more flexible allocation policies that allow better locality of reference and can be adapted to a wide range of peripheral and processor characteristics.The new file system clusters data that is sequentially accessed and provides two block sizes to allow fast access to large files while not wasting large amounts of space for small files.File access rates of up to ten times faster than the traditional UNIX file system are experienced.Long-needed enhancements to the programmers' interface are discussed.These include a mechanism to place advisory locks on files, extensions of the name space across file systems, the ability to use long file names, and provisions for administrative control of resource usage.

The idea of a capability which acts like a ticket authorizing the use of some resource was developed by Dennis and Van Horn as a generalization of addressing and protection schemes such as the code- words of the Rice computer, the descriptors of the Burroughs machines, and the segment and page tables in computers such as the GE-645 and IBM 360/67. Dennis and Van Horn generalized the earlier schemes by extending them to include not just memory, but all systems resources: memory, processes, input/output devices, and so on; and by stressing the explicit manipulation of access control by nonsystem programs. The idea is that a capability is a special kind of address for an object, that these addresses can be created only by the supervisor, and that in order to use any object, one must address it via one of these addresses. The name comes from the fact that having one of these special kinds of addresses for a resource provides one with the capability to use the resource.