General Exception and Protection Faults

If you can go through the same sequence and get the same error repeatably, there is a code error or corrupted module that must be fixed. If, however, the error occurs only some of the time, it is related to a transient state of the operating system and the other programs multi-tasking at the time.

General Exception and Protection errors typically occur in the DOS operating system. Even when running nothing but Windows applications, DOS still generates the error. This is caused by the dependency of Windows to use conventional memory and to access the DOS Stack and Segment registers to service application resource requests and hardware access.

When Windows is loaded, it turns off DOS so that it can take over. During its operation, Windows continually turns DOS on and off as needed, so that DOS can service its many requirements. It is important to understand that DOS was designed to only run one program at a time, and to service that programs resource requests and hardware requirements. When Windows is in control, it emulates many DOS session's in an attempt to parallel DOS functions simultaneously.

Because Windows uses DOS in each of these parallel processes, occasionally the Windows emulation of DOS looses track of a pointer address and allows what is called an illegal instruction. It attempts to let DOS execute an instruction from an invalid address causing the system to become unstable. This occurs when Windows attempts to load a program on top of a previously loaded program's segment address, causing the system to generate an error or totally crash the system.

The ATLast program monitors the DOS stack and the state of the operating system's registers for errors. If an error is detected, ATLast resets the segment register (up to three times) in an attempt to correct the problem, and then requests DOS to execute the offending instruction again. When the error is caused by a transient interaction between the current programs and the operating system, ATLast clears the illegal condition and prevents the user from experiencing the pain and suffering of a system crash.

"Back to the Future" aka RYBS' Home Page