Monday, October 30, 2000		Lead Article

by Vipul Verma

UNDOUBTEDLY, a computer performs many operations correctly at a considerable speed and is, therefore, often considered super-intelligent. However, the right performance is under a given set of parameters. If there is even a slight change in these, an error may occur.

The parameters here refer to the operating system, software and the hardware. If some critical files of a software have been removed, it will give an error. Similarly, if the operating system gets corrupted, a computer may give errors. In case of certain hardware failures also, a computer may give error messages and create problems for the user.

Errors are just like symptoms of a disease. You can try to find a solution only after you diagnose and understand them. Errors could be visible or invisible. In case of visible errors, the CPU detects and gives a warning window. It contains the details of the error encountered by the CPU. However, these errors are displayed in technical language, which a normal computer user may not be able to comprehend. In case of invisible errors, one does not get warning messages but the computer performs erratically. It may even hang. While invisible errors cannot be precisely defined, visible errors can be explained and interpreted in a simple language. Following are some of the error messages that one might have come across some time or the other.

General protection fault: Interrupt 13 also represents this error. This error means any condition, which is not covered by any of the other processor exceptions, will result in a general protection fault. The exception indicates that this program has been corrupted in memory usually resulting in immediate termination of the application. Thus, whenever one gets this kind of error, the program stops responding and gets terminated automatically. Thus, general protection faults are linked more to the memory.

In a nutshell, all protection violations that do not cause another exception cause a general protection exception. This includes, but is not limited to:

• Exceeding the segment limit when using the CS, DS, ES, FS, GS segments. This is a common bug in programs, usually caused by miscalculating memory required in an allocation.
  
  

• Transferring execution to a segment that is not executable.
  
  

• Writing to a read-only or a code segment.
  
  

• Loading a bad value into a segment register.
  
  

• Using a NULL pointer. A value of 0 is defined as a null pointer. In protected mode, it is always invalid to use a segment register that contains 0.

The general protection fault can be tackled by the hit-and-trial method and with due diligence, the problem can be solved.

As a first step in solving any computer-related problem, one must ascertain what exactly the problem is and whether it is related to hardware or software. The easiest way is by starting a computer in safe mode. If in safe mode and the computer starts properly, it could mean that the problem is more likely to be linked with the driver or a specific program. Since Windows loads only the necessary set of files in the safe mode, any extra divers or program files are not taken into consideration. Thus, proper starting in safe mode more significantly reflects the problem in software. However, if the computer fails to boot properly even in the safe mode, the problem can be related to hardware or Windows core files.

This test applies to all Windows-related errors and faults, including general protection fault also. Thus, after testing the system in safe mode, if the error persists, as it used to be in case of normal mode, then one needs to reinstall Windows again Even after reinstallation if the error remains, it shows that some of the hardware component has got corrupted.

However, if the error does not occur, use the System configuration utility tool (Msconfig.exe) to minimise conflicts that may be causing error in normal mode. The following is the procedure: Click Start>Programs>Accessories>System Tools> System Information. Now on the Tools menu, click System Configuration Utility, then on the General tab, click Selective Startup, and then click to clear the following check boxes: Process config.sys file, Process autoexec.bat file, Process winstart.bat file (if available), Process system.ini file, Process win.ini file. Load startup group items. Now Click OK, and restart the computer in normal mode.

If you do not get the error message, you need to perform the test by check marking the above-mentioned six items in the selective startup menu individually in order to reach the conclusion. Each time select an item and apply this test. Continue this process until all items in Selective startup are selected. If you select an item and problem occurs, click the tab of the corresponding item in Selective startup and remove half of the check boxes. Click OK, and then restart computer. Continue this process until you narrow down the setting that is causing the problem. Now, as the last step if you can restart the computer successfully when all items are checked, run the System configuration utility, click to select Normal startup, click OK, and follow the steps on the screen to restart the computer. Using this procedure, you can pin-point general protection fault problem and resolve it.

Fatal exception errors: Like the general protection fault, the fatal exception errors are also errors related to programs. They are referred to the codes returned by a program when access to an illegal instruction has been encountered, or invalid data/ code has been accessed. The privilege level of an operation is then invalid. When any of these situations occurs, the processor sends the fatal exception error message to Windows. In most of the cases, the error proves to be really fatal as it means the closure of either the application or Windows. Normally, a fatal expression is expressed in the following format.

A fatal exception <XY> has occurred at xxxx:xxxxxxxx.

Here the <XY> represents the actual processor exception from 00 to 0F. The xxxx:xxxxxxxx represents the enhanced instruction pointer to the code segment and the 32-bit address is the actual address where the exception occurred.

Normally, there cannot be a general solution for handling the fatal exception errors as there could be hundreds of different reasons like conflicting drivers, terminate-and-stay-resident programs (TSRs), and other settings that are loaded when your computer starts. They could all result in fatal exception errors. The best way to deal with this is to narrow down the problem first and then work out a solution. For narrowing down the problem, cleanboot the system.

Invalid VxD dynamic link call from <A> to device <B>, service <C>: This error is all about drivers. If you get this error message in any of Windows application, it is primarily because of an incompatibility between driver versions, or a damaged or missing driver. This error may also occur if the computer is not configured properly or because a device driver has been added or removed from the computer recently. Thus, in these types of error messages one should not try to alter the Windows settings in order to sort out the problem. As a practical solution, try uninstalling and then reinstalling any programs or components that were installed recently, or the program that is giving errors.