Illegal operation

Hi Rita

Illegal operation - A microprocessor has a finite number of instructions it understands, and each instruction is represented by a number known as an "opcode." The opcode 43 might mean "add," the opcode 52 might mean "multiply," etc. If the microprocessor is executing a program and comes to an opcode that it does not recognize or that it cannot execute because of the current state it is in, then the microprocessor stops to complain. The operating system handles this complaint by shutting down the offending program. Illegal opcodes normally come from software jumping to a location in memory that does not contain valid program information.

All of these problems are caused by human error on the part of a programmer. The programmer is not diligent enough to catch an exception, or allows the program to access invalid memory. Sometimes, the root cause is incompetence or inexperience, but in many cases it is the complexity of today's programs. There are hundreds of exceptions and often millions of blocks of memory that a program manages in an intricate, layered environment. One false move and the application crashes -- software is very brittle. Testing finds many errors, but usually it does not find them all.


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