Parity Error Messages May Indicate Bad Memory

When you are running Windows 95, you may receive frequent (every 10 or 20 minutes) "Parity Error" messages on a blue screen. When you receive such a message, you must restart the computer.

Parity errors are usually caused by defective memory chips in the computer. For more information about parity errors, please see the following article in the Microsoft Knowledge Base: Parity errors can also be caused by:

• Mismatched RAM. That is, mixing different types of SIMMs (such as parity and non-parity RAM) on the motherboard.
• Incorrect RAM for the motherboard. For example, non-parity RAM on a motherboard requiring parity RAM.
• Non-proprietary RAM on a motherboard that required proprietary RAM.

There are two methods you can use to identify whether defective memory chips are causing the problem:

• Remove or replace memory chips in the computer to see if the problem is resolved.
• Try limiting the amount of memory that Windows 95 uses. To do so, follow these steps:
  
  
  1. Use any text editor (such as Notepad) to edit the System.ini file.
  2. Add the following line in the [386Enh] section of the file
     MaxPhysPage=<nnn>
     where <nnn> determines the amount of memory you want Windows 95 to use.
     
     To limit Windows 95 to the first 16 MB of memory, add the following line:
     MaxPhysPage=FFF
     To limit Windows 95 to the first 8 MB of memory, add the following line:
     MaxPhysPage=7FF
     To limit Windows 95 to the first 4 MB of memory, add the following line:
     MaxPhysPage=3FF
  3. Save and then close the System.ini file.
  4. Restart your computer.

For additional information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

Defective memory chips may not be detected by memory checking tools. Some memory checking programs are not adequate tests because they do not test RAM in the same way that Windows uses RAM. Most memory checkers use read/write cycles when scanning memory. Since Windows is executing code from memory, it uses execute cycles. Execute cycles are different from read/write cycles and are more vulnerable to parity errors. It is possible for memory checking programs to find parity errors if the memory is extremely faulty. Bad memory chips can also cause the following situations:

• Fatal Exception errors
• Himem.sys load failures in normal or Safe mode
• Random lockups
• The computer may stop responding (hang) as soon as you turn it on