not allow similar access to other libraries or unaffiliated readers; the system does not support file sharing. On request, a library may supply another library with content to effect a repair, but only if the requesting library proved that in the past that it had a good copy by voting with the majority. If the reader's browser no longer supports the format in which the copy was collected, a format migration process can convert it to a current format. These limits on the use that may be made of preserved copies of copyright material have been effective in persuading copyright owners to grant the necessary permission. The LOCKSS approach of selective collection with permission from the publisher, distributed storage, and restricted dissemination contrasts with, for example, the Internet Archive's approach of omnivorous collection without permission from the publisher, centralized storage, and unrestricted dissemination. The LOCKSS system is far smaller, but it can preserve subscription materials to which the Internet Archive has no access. Since each library administers its own LOCKSS peer and maintains its own copy of preserved material, and since there are libraries doing so worldwide (see the list of participating libraries below), the system provides a much higher degree of replication than is usual in a fault-tolerant system. The voting process makes use of this high degree of replication to eliminate the need for backups to off-line media, and to provide robust defenses against attacks aimed at corrupting preserved content. Importance In addition to preserving access, libraries have traditionally made it difficult to rewrite or suppress printed material. The existence of an indeterminate but large number of identical copies on a somewhat tamper-resistant medium under many independent administrations meant that attempts to alter or remove all copies of a published work would likely both fail and be detected. Web publishing, based on a single copy under a single administration, provides none of these safeguards against subversion. Web publishing is, therefore, an amenable tool for rewriting history. By preserving many copies under diverse administration, by automatically auditing the copies at intervals against each other (and, in the future, against the publisher's copy), and by alerting libraries when changes are detected, the LOCKSS system attempts to restore many of these safeguards in the now digital world of publication. Implementation Prior to implementing a LOCKSS system, some questions need to be considered carefully in order to make sure the content is