PURPOSE: To rewrite contents of a nonvolatile memory by turning on or resetting a computer system while pressing a keyboard.

CONSTITUTION: When the power is turned on with a key A(O) of the keyboard 13 pressed, a program loader stored in an ROM 14 rewrites the contents of the nonvolatile memory 12 to zero and loads a program on an RAM 16 from a floppy disk 15. The program loaded on the RAM 16 sets a CRT display 11 to a 80 columns ×25 lines display mode by referring zero of the memory 12, and processes the successive operation. When the power is turned on with the key B(1) of the keyboard pressed, the program loader stored in the ROM 14 rewrites the contents of the memory 12 to 1 and loads a program on the RAM 16 from the disk 15. The program loaded sets the CRT display 11 to a 40 columns ×25 lines display mode by referring 1 of the memory 12 and processes the successive operation.