Change log historian system for memory shared by multiple workstations

Abstract

A communication-efficient change log historian allows workstations having images of a shared memory to remain correlated to the shared memory. The system comprises one or more workstations connected to a microprocessor-based device which includes a memory device. The memory device includes the shared memory, and also stores a memory change list and a memory change index. The memory change list forms a list of changes which have been made to the information stored in the shared memory area, and the change index is indicative of the location of the most recent entry to the memory change list. The workstations maintain an image of the shared memory area, and store workstation change indexes which are indicative of the most recent entry to the memory change list which has also been implemented to respective images of the shared memory area in the workstations. The workstation regularly compares the workstation change index with the memory change index, thereby permitting the workstation image to be dynamically correlated with the shared memory. Advantageously, the system implements updates only when the contents of the shared memory have changed, and updates only those portions of the shared memory which have changed. The system also allows for the dynamic correlation of the workstation image with the shared memory, and allows the microprocessor-based device to be a passive participant in this process.