Computer processor system with software protection.

摘要

A computer processor system includes a protection unit (10) for preventing execution of programs not authorised for use with that system while allowing the user's own programs to be executed unimpeded. A RAM (9) in the protection unit (10) is addressed by a buffer (8) holding the function code of a retrieved instruction and outputs a microprogram step number. The function code is larger than is required to specify its effect. Some values of the function code are unprotected and for them the RAM 9 always outputs the correct step number. Other values are protected and for them the correct step number is output only if the value has been enabled by writing the step number into the RAM 9 in response to information input from a removable device (11). Unprotected values may be used in the user's program. The protected values provide aliases for the unprotected values and may be used in a supplier's program.