MEMORY SYSTEM

PURPOSE:To holds the logging date when a power supply is turned off with addition of the simple hardware and with use of a program by using a cache memory as a back-up memory. CONSTITUTION:When a power supply 9 is turned off, an interruption is applied to a CPU 1 with detection 9.1 of the cut-off of the supply 9. Thus the CPU 1 carries out a power interruption program 5.2 stored in a ROM 5. The program 5.2 reads the address of the logging date 2.2 out of a main memory 2. Then the logging data is stored in a cache memory 6 and the CPU 1 stops its operation. Both the memory 6 and a cache control part 7 are backed up by a battery 8 and therefore the contents of the memory 6 and the part 7 are held even in a power cut-off state. Thus the logging data 2.2 is read out of the memory 6 backed up by the battery 8. As a result, the logging data is backed up without using any exclusive memory to which a logging address is especially allocated.