File Integrity in a Disc-Based Multi-Access System

Abstract

The operating system that is used on the Titan computer at Cambridge University includes procedures for the organization and maintenance of file storage. About 10,000 files, belonging to some 700 users, are held on a magnetic disc that has a total capacity of 128 million characters. For the past 4 1/2 years this system has been used on a scheduled 20-hour day to provide job-shop and multiple-access facilities to a total user population of about 1500 persons. The file management software is described here in some detail. An overview of the system will be found in reference [1], and further details will be found in references [2] and [3]. Under the heading of file management we include these procedures which are a concerned with file identification, file privacy, space allocation and file integrity. In this context a file may be any ordered string of data and it is of no interest to the file management software to know what that data represents. In practice each file is held as a string of blocks (one block can accommodate 4096 characters). A quite distinct set of data handling routines provide the user with convenient means of processing the contents of a file. The file management software consists of complete programs that operate under supervisor control in the manner normally associated with other users of the system.