Memory Parity Errors

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Explanation: During the BIOS POST process a memory parity error was detected within the system memory. Parity checking is used to detect memory corruption between the time that data is written to memory and the time that it is read back. This error message means that there is a problem associated with the system memory itself, usually not your motherboard, but at the onset don't rule anything out, take one step at a time. Depending on the quality of the system BIOS, you may see some specifics on screen about what part of memory caused the error.

Diagnosis: There are many possible causes of memory parity errors, some of them only related indirectly to the memory, or even having nothing to do with the memory at all. In particular, a memory error at start up is often indicative of a wide variety of possible problems.

Background: Memory is an electronic storage device, and all electronic storage devices have the potential to incorrectly return information different than what was originally stored. Some technologies are more likely than others to do this. DRAM memory, because of its nature, is likely to return occasional memory errors. DRAM memory stores ones and zeros as charges on small capacitors that must be continually refreshed to ensure that the data is not lost. This is less reliable than the static storage used by SRAMs.

Data stored in memory is in the form of either a zero or a one, the standard in a digital system. This in itself helps to eliminate many errors, because slightly distorted values are usually recoverable. For example, in a 5 volt system, a "1" is +5V and a "0" is 0V. If the sensor that is reading the memory value sees +4.2V, it knows that this is really a "1", even though the value isn't +5V. Why? Because the only other choice would be a "0" and 4.2 is much closer to 5 than to 0. However, on rare occasions a+5V might be read as +1.9V and be considered a "0" instead of a "1". When this happens, a memory error occurs.

There are two types of errors that can usually occur in a memory system. The first is called a repeatable or hard error. In this situation, a piece of hardware is broken and will consistently return incorrect results. A bit may be stuck so that it always returns "0" regardless of what is written to it. Hard errors usually indicate loose memory modules, bad chips, motherboard defects or other physical problems. They are relatively easy to diagnose and correct because they are consistent and repeatable.

The second kind of error is called a transient or soft error. This occurs when a bit reads back the wrong value once, but subsequently functions correctly. These problems are, understandably, much more difficult to diagnose, but they are also, unfortunately, more common. Eventually, a soft error will usually repeat itself, but it can take anywhere from minutes to years for this to happen. Soft errors are sometimes caused by memory that is physically bad, but at least as often they are the result of poor quality motherboards; memory system timings that are set too fast; static shocks; or other similar problems that are not related to the memory directly. In addition, stray radioactivity that is naturally present in materials used in computer systems can cause the occasional soft error. On a system that is not using error detection, transient errors often are written off as operating system bugs or random glitches.

The predictability of memory errors, or the rate at which we might be able to calculate them has always been a matter of considerable debate. There's no dispute that today's DRAM chips are far more reliable than those of five or ten years ago, however this has given rise to an increase in the number of system BIOS developers that remove error detection support from their BIOS code at the demand of the large system manufacturers. Unfortunately though, all of these factors tend to worsen the memory problems in modern systems rather than resolve them. More DRAM memory is being used today than ever before. Just 15 years ago the typical system had 1 MB to 4 MB of memory, while today's systems usually have 64 MB to 256 MB and more. Much of this has been caused by the sudden drop in RAM prices in the last three years. Today's systems are running considerably faster than they used to, with the typical memory bus running from 3 to 20 times the speed of those of older machines we remember. Unfortunately the quality level of the average PC is way down from the levels of 10 years ago. Today we are seeing more hardware related problems then ever before. As we have stated throughout this Web site, you do get what you pay for. If you were to inspect today's E-Machines and some of the products pushed out the door by the cut-throat assembly houses, you could easily identify that the RAM used is often of marginal quality.

In any event, regardless of how often memory errors occur, they do occur. How much damage they create depends largely on the type of data being handled when the errors occur. If you are playing your favorite game and one of the bits controlling the color of a pixel is inverted from a one to a zero on a screen redraw, who cares. However, if you are defragging your hard drive and the memory location containing information to be written to the file allocation table is corrupted, the issue takes on a whole new importance.

There's only two forms of  true protection from memory errors; One is to use some form of memory detection or correction protocol, and the other is by purchasing quality components and not neglecting your system. Some protocols can only detect errors in one bit of an eight-bit data byte, while others can detect errors in more than one bit automatically. Others can both detect and correct memory problems, seamlessly.

You can learn more about memory related issues at our Performance Center under Memory.

More Information and Troubleshooting Memory Problems

New or Recently-upgraded Systems

Preliminary diagnostic tests or troubleshooting procedures have identified the memory is suspected of being bad, or the system memory is a possible cause of an unknown system problem.

Diagnosis: There are three common categories of memory problems on a new system. The first is improper configuration, or using the wrong type of memory. The second is incorrect installation. The third is hardware failure of the memory module itself.


Existing Systems

Diagnosis: Sudden memory on existing systems are extremely unusual, as most memory problems occur when a system is assembled or when it is upgraded. A failure on an existing system usually means that the system itself has a problem or that the cause was external to the memory module. Some possible causes are system overheating, power supply problems, external power surges or brownouts and lightening damage. System overheating and power problems are the most frequent causes of hardware failures.



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