MEMORY PROTECTION SYSTEM PROVIDING FIXED, CONDITIONAL AND FREE MEMORY PORTIONS CORRESPONDING TO RANGES OF MEMORY ADDRESS NUMBERS

摘要

A method and apparatus for flexible protection against overwriting and destruction of the contents of selected portions of a computer memory device formed of a multiplicity of memory units. Each memory unit is assigned a unique memory address number which serves to identify the memory unit in instructions to write data into the memory. The address numbers are segregated into ranges of numbers defining separate memory portions to be protected, with the numbers at the limits or boundaries of the ranges being entered in registers which can be reset to flexibly determine the protected ranges. The memory device is separated in this fashion into three different portions: one permitting free writing access to the memory units, one withholding all writing access to the memory units, and one being conditioned to grant or withhold writing access according to the setting of a device such as flip-flop which can be arranged for manual or programable control. Whenever an instruction to alter a memory unit arises, the associated address number is entered in a register and compared by means of digital comparators with the range boundary numbers in their registers. Gate means grant or withhold access to the memory unit in accordance with the comparison, thereby controlling the insertion of data into each memory unit and providing protection for selected portions of the memory device.