Memory back up system with one cache memory and two physically separated main memories

Memory backup apparatus for a fault-tolerant computer system having system memories for storing data, a processing element for performing a plurality of data processing tasks and computations, said processing means generating write control signals to cause information to be written into said system memories and task control signals for controlling said system during a context switch, and means for monitoring fault occurrences in said computer system and for generating fault signals, said backup apparatus comprising,

• a first memory area and a second, physically separate memory area located in said system memories, said memory areas storing duplicate copies of data and subsequent computational results generated by said processing element;
• a temporary storage area, said storage area generating a full signal when a predetermined number of storage locations in said memory has been written to;
• first means responsive to said write signals for writing data from said first memory area into said temporary storage area and for writing computational results produced by said processing element into said temporary storage area;
• second means responsive to said full signal and to said task control signals for writing selected portions of said temporary storage area into said first memory area when said temporary storage area is full or when said task control signals indicate a context switch is requested, said second means producing a completion siganl when said writing has been completed;
• third means responsive to said completion signal and to said fault signals for writing said selected portions of said temporary storage are into said second memory area when the writing of data from said temporary storage area into said first memory area had been completed without a fault condition being detected;
• and
• means for writing the contents of said second memory area into said first memory area and for restarting the data processing task using data stored in said second memory area if a system failure has occurred after the beginning of a storage operation from said temporary storage area to said first memory area but before said storage operation has been completed.

A method for backing up data in a computer system having a plurality of main memories, including a first main memory, a second, physically separate main memory area and a non-write-through cache memory, a processing element for performing data processing tasks and computations on data, and means for detecting the occurrence of a fault condition, said method comprising the steps of:

• A. placing duplicate copies of data in said first and second main memory area;
• B. storing copies of computational results generated by said processing element in said cache memory during data processing of a task;
• C. temporarily stopping data processing and transferring a copy of a set of computational results stored in said cache memory to said first main memory area when a data processing task has been completed, when a contact switch has been initiated or when said cache memory becomes full to update said first retry data copy;
• D. transferring a copy of said set of computational results stored in said cache memory to said second main memory area to update said second retry copy only when the transfer of said set of computational results between said cache memory and said first main memory area has been completed without a fault condition being detected;
• E. resuming data processing only if the writing of data from said cache memory into said second memory area has been completed without a fault condition being detected;
• and
• F. writing the contents of said second memory area into said first memory area and restarting the data processing task using data retry stored in said second memory area if a system failure has occurred after the beginning of a storage operation from said cache memory to said first memory area but before said storage operation has been completed.

A method for backing up data in a fault-tolerant computer system having first, second and third system memories for storing data, a processing element for performing a plurality of data processing tasks and computations, and means for detecting the occurrences of a fault in said computer system, said method comprising the steps of:

• A. placing duplicate copies of data in said first and third memories and, during the processing of a task, writing data associated with said task from said first memory into said second memory and writing computational results produced by said processing element into said second memory;
• B. detecting a context switch condition or a memory full condition in which a predetermined number of storage locations have been written to;
• C. after a context switch has been initiated or after a memory full condition has been detected copying selected portions of said second memory into said first memory;
• D. copying said selected portions of said second memory into said third memory when the copying of data from said second memory into said first memory area has been completed without a fault condition being detected;
• and
• E. writing the contents of said third memory into said first memory and restarting the data processing task using data stored in said third memory area if a system failure has occurred after the beginning of a storage operation from said second memory to said first memory but before said storage operation has been completed.