Patent US 4,079,447

A method and apparatus for use in electronic computer for altering a stored program. The deletion of an instruction from a main memory storing it results in a compression of the program that included the deleted instruction in order to conserve memory space. The insertion of an instruction in a program stored in a main memory results in the shifting of subsequent instructions stored therein. The memory may be divided into arbitrary sections in response to an instruction enabling the search of a particular subroutine to be shortened. The subroutines in the program which can be reached each have a corresponding program level register. At each subroutine jump instruction the contents of the program level registers are shifted up in order to save the current program level register contents.