WINDOWS kbhw kbdisplay kbprb The information in this article applies to:
SUMMARYParity error messages are caused by the generation of nonmaskable interrupts (NMIs). A clean, uncorrupt installation of Windows cannot generate an NMI, therefore it is not possible for a clean, uncorrupt installation of Windows to cause a parity error. MORE INFORMATION
Parity is a very basic check of information integrity. Each byte (8 bits)
of RAM storage actually takes nine bits of information. Eight bits are used
for the data and the last bit (the "parity bit") is used to store the
parity of the data.
Common Causes of Parity ErrorsOne cause of parity errors is faulty memory. The most foolproof way to resolve this problem is to swap out each piece of memory until the problem disappears. Make sure you are using good, quality memory and the memory is properly seated in the computer. Memory checking programs are not adequate because they don't test the memory the way that Windows uses it. Most, if not all, memory checkers use read/write cycles when scanning memory. Since Windows is executing code from the memory, it uses execute cycles. Execute cycles are physically 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.Sometimes parity errors are caused by mismatched memory speeds. The CPU might be accessing the memory faster than the memory is capable of handling requests. A possible workaround is to increase the number of wait states in the CMOS setup. This option is not available on all machines and doesn't always work. In short, increasing the number of wait states directs the CPU to wait for a predetermined amount of time between memory reads. This slows the machine down because it now takes longer to access memory. Generally, this option can be set to Zero, One, or Two wait states. The higher the number, the longer it waits between memory cycles. In addition, try to keep the same speed of RAM installed in your computer. If you have to mix speeds, make sure that you have the same speed RAM installed in each Bank. Banks are usually sets of four memory chips on the motherboard. Supporting hardware, like video cards, can often cause parity errors. Because the devices occupy memory in the UMB, read/write data to these devices can also cause parity errors. The best way test this is to replace the device with one that is working correctly. Also faulty power supplies can cause parity errors. Another known cause for parity errors is the PARITY BOOT B Virus. What is Parity?There are two versions of Parity: Odd and Even. The Parity BIT is set on or off depending on the count of ON bits, or 1's, in the data, usually a byte.Examples11011010 (Parity would be set to 1 to make the number of ones even.)11110111 (Parity would be set to 0 to make the number of ones odd.) Memory for the PC is designed such that there is an extra chip, or extra BIT, set aside for parity. This chip will hold the parity for a byte of memory. This is why there is often 9 chips on a memory SIMM, or the chips themselves are labeled 256x9's or 1Megx9's, and so on. A parity error will be generated when a piece of code is executed in a faulty memory address. During the fetch or pre-fetch cycle of the CPU, the point where the CPU receives an instruction from memory to execute, the hardware checks the fetched code for parity. If that fetch fails, an exception error is generated. This is done to safe-guard the CPU from executing an instruction that is not viable. During a regular memory fetch, that is, data reads, parity is not checked. This is why a memory checker will normally be unable to find parity errors. The only program that will check memory for parity problems correctly is a program that executes code in the RAM addresses in question. Windows 3.0 and 3.1 are such programs. In Windows 3.0, the mechanism for checking parity errors did not function correctly and instead generated UAE's. These UAE's were a result of the parity errors not being caught and the code continuing to run in the faulty memory. NOTE: You cannot check memory for parity problems by creating a RAMDRIVE, copying a program to it, and executing the program. The program is still stored as data in the RAMDRIVE. When run, the program is copied into conventional memory before it is executed. For information on how to use a RAMDRIVE to troubleshoot memory, please see the following article(s) in the Microsoft Knowledge Base: Q142546 How to Use a RAM Drive to Troubleshoot Memory Additional query words: 3.00 3.00a 3.10 3.11.exe execute paroty parety parityerror
Keywords : win31 win30 |
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Last Reviewed: September 17, 1999 © 2000 Microsoft Corporation. All rights reserved. Terms of Use. |