Abstract: In storing data in one file, consisting of a plurality of blocks of data, a first code is generated by converting a password and a predetermined portion of each of the blocks of data. This portion may be, for example, the data block itself or identification information such as a name. The code is stored in correspondence to the stored data. In reading the stored data, a second code is generated by performing the same conversion on the password and the predetermined portion of the stored data. A comparison is made between the generated second code and the first code stored. Failure of the two to match indicates that an improper rewrite has occurred. In such a case, that occurrence may simply be noted, access to the data may be prohibited; more generally, what processing is performed, or is permitted, is varied according to the result of the comparison.

Abstract: A lockout avoidance circuit is provided for a plurality of nodes which generate lock requests for a shared resource such as a memory location. The circuit insures that lock requests are eventually satisfied. A lock queue includes a plurality of registers pipelined together. Lock requests only enter the lock queue if they are refused access to a shared resource a predetermined number of times. A first register is the head of the queue and the last register is the bottom of the queue. An enabling circuit allows the queue to store in the registers lock requests received from the different nodes in the order in which they are initially refused service. The enabling circuit operates the queue by pushing the stored lock requests toward the head of the queue each time the head entry in the queue is serviced. The lockout avoidance circuit is implemented at each level of the system wherein a lockout condition can occur.