. The scheme defines how this is done efficiently in terms of minimal additional storage space and minimal reduction in throughput time while at the same time providing maximum security. Preferably according to the method of the third aspect of the present invention there is also provided supervising means (a Supervisor) separate of a central processing unit (CPU) of the computer system for controlling the performance of read, write and format operations upon the information stored on the storage medium so as to allow, restrict or prevent such operations depending upon the type of information stored within a sector and type and status of the partition within which the sector is located, the supervising means causing a reset to be required of the computer system should an attempt be made to perform a prohibited read, write or format operation, said reset causing memory to be cleared and the operating system to be loaded. 