12.3 Common Windows Operating System Problems
12.3.3 Windows memory usage problems
Memory usage errors occur when the operating system or an application attempts to access a memory location that is unallocated. When this type of conflict occurs, the unallocated memory location becomes corrupted and usually results in the operating system crashing. This could occur if a user is running more than one application at a time and one of the applications attempts to use another application's memory space. When this happens, the operating system will generate an error message or just stop processing altogether and lock up. This typical error message is "This operation has performed an illegal operation and is about to be shut down".

Some memory usage errors are non-fatal, meaning that they will not lock up the application or cause the system to lock up. These types of memory usage errors give an option to continue working or just shut down the application. It is recommended that users do not continue working with the application because it can become unstable and lock up, causing a loss of unsaved data.

In the event that a Windows memory error affects the Windows core files (KRNLXXX.EXE, GDI.EXE, USER.EXE), restart the Windows operating system.

Windows Resources Low Issues
It is a good idea to know the level of the operating system resources. When the Windows resource level gets too low, it can cause the applications or the operating system to lock up. This type of error indicates that the operating system is running out of real and virtual memory. In general, it becomes obvious that Windows resources are getting low when the system performance begins to degrade and run very slowly. This usually occurs when many applications are running at the same time or when the system has not been restarted in a long time. The system tray in the lower right hand corner of the screen contains programs that are constantly running in the background even though they are not being used. Because they are constantly running, they use system resources. It is a good idea to disable or remove any unneeded icons in the system tray in order to free up more resources for other applications.

General Protection Faults (GPF) Problems
A General Protection Fault (GPF) occurs when one of the operating system applications attempts to access an unallocated memory location. General Protection Faults are usually the result of programs that use illegal instructions to access areas of memory that have been protected. In earlier versions of Windows a GPF would crash the system and require the system to be rebooted, thus losing any unsaved data. The latest versions of Windows remain stable after a GPF so that users can close the error message and save their data before closing the application or restarting the system.

Typical causes of General Protection Fault include running applications that are not written for the Windows operating system, selecting the wrong machine or network during installation, or using incorrect versions of DOS in the system. The CONFIG.SYS and AUTOEXEC.BAT file that contains incompatible or unsupported programs or drivers could also be a cause.