Hardware Reference
In-Depth Information
predicted by some that the soft error rate of a 64MB DRAM is double that of a 16MB
chip, and a 256MB DRAM has a rate four times higher. As memory sizes continue to in-
crease, it's likely that soft error rates will also increase.
Unfortunately,thePCindustryhaslargelyfailedtorecognizethiscauseofmemoryerrors.
Electrostaticdischarge,powersurges,andunstablesoftwarecanmuchmoreeasilyexplain
awaytherandomandintermittentnatureofasofterror,especiallyrightafteranewrelease
of an operating system (OS) or major application.
Although cosmic rays and other radiation events are perhaps the biggest cause of soft er-
rors, soft errors can also be caused by the following:
•
Power glitches or noise on the line
—Thiscanbecausedbyadefectivepowersupply
in the system or by defective power at the outlet.
•
Incorrect type or speed rating
—Thememorymustbethecorrecttypeforthechipset
and match the system access speed.
•
RF (radio frequency) interference
—Caused byradio transmitters inclose proximity
tothesystem,whichcangenerateelectricalsignalsinsystemwiringandcircuits.Keep
inmindthattheincreaseduseofwirelessnetworks,keyboards,andmousedevicescan
lead to a greater risk of RF interference.
•
Static discharges
—These discharges cause momentary power spikes, which alter
data.
•
Timing glitches
—Data doesn't arrive at the proper place at the proper time, causing
errors. Often caused by improper settings in the BIOS Setup, by memory that is rated
slower than the system requires, or by overclocked processors and other system com-
ponents.
•
Heatbuildup
—High-speedmemorymodulesrunhotterthanoldermodules.RDRAM
RIMM modules were the first memory to include integrated heat spreaders, and
many high-performance DDR, DDR2, and DDR3 memory modules now include heat
spreaders to help fight heat buildup.
Mostoftheseproblemsdon'tcausechipstopermanentlyfail(althoughbadpowerorstatic
can damage chips permanently), but they can cause momentary problems with data.
How can you deal with these errors? The best way to deal with this problem is to increase
thesystem'sfaulttolerance.Thismeansimplementingwaysofdetectingandpossiblycor-
rectingerrorsinPCsystems.Threebasiclevelsandtechniquesareusedforfaulttolerance
in modern PCs:
• Nonparity
• Parity
