Page "Machine code" Paragraph 3

Every processor or processor family has its own machine code instruction set.

Instructions are patterns of bits that by physical design correspond to different commands to the machine.

The instruction set is thus specific to a class of processors using ( much ) the same architecture.

Successor or derivative processor designs often include all the instructions of a predecessor and may add additional instructions.

Occasionally a successor design will discontinue or alter the meaning of some instruction code ( typically because it is needed for new purposes ), affecting code compatibility to some extent ; even nearly completely compatible processors may show slightly different behavior for some instructions, but this is seldom a problem.

Systems may also differ in other details, such as memory arrangement, operating systems, or peripheral devices.

Because a program normally relies on such factors, different systems will typically not run the same machine code, even when the same type of processor is used.