1. A method of operating a microcomputer provided with nonvolatile storage means storing a check data signal and read/write volatile storage means of the type that store bit values only while power is supplied thereto, said method enabling the volatile storage means to be tested to determine if the contents thereof have changed in response to power not being supplied thereto, the check data enabling the volatile storage means to be checked to determine if data stored therein has changed as a result of power not being supplied thereto, comprising storing the check data signal in an allocated portion of said read/write storage means and storing in the remaining portion of said read/write storage means other data needed to perform computer functions, detecting a match or mismatch between the check data signal stored in said nonvolatile storage means and the data signal stored in said allocated portion of said read/write storage means each time power is applied to the microcomputer, setting all bits stored in said remaining portion of said read/write storage means to a predetermined state and writing said check data signal stored in said nonvolatile storage means into said allocated portion of said read/write storage means in response to a mismatch being detected, and operating said microcomputer in accordance with the normal computer functions thereof using data stored in said remaining portion of said read/write storage means in response to a match being detected between the stored check data in said nonvolatile storage means and the data signal stored in said allocated portion of said read/write storage means.