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Cosmic Rays: what is the probability they will affect a program?
Is this just a tongue in cheek expression or is this really true, and if so, what precautions should we take in software (or these precautions hardware only)?
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You're probably thinking of cosmic rays -- high energy charged particles, rather than photons -- and yes, they can cause bit flips and other such effects due to the ionization that can occur when they interact with the atoms in semiconductors.
A bit flip occurs when you're copying data and one of the bits changes so that it's incorrect. A value of 1 incorrectly becomes a zero, or vice versa. Bit flips that lead to bug checks are a common way that Windows detects a hardware problem (e.g., bad memory, an overheating CPU).
Cosmic radiation and fluctuations in power or temperature are the most common naturally occurring causes. Research from 2010 estimated that a computer with 4GB of commodity RAM has a 96 percent chance of experiencing a bitflip within three days.
Research has shown that a computer with 4GB of memory has a 96% chance of having a random “bit flip” every three days. That's a crazy high chance of data corruption occurring on your computer.
Well, I did dig up this paper, which claims that your RAM will get bit alterations from "Atmospheric Neutrons" (aka: Cosmic Rays) at a rate of about 1.3*10^-12 /bit/hour.
An article by Berke Durak uses that to calculate that your probablilty of having at least one bit error in 4 gigabytes of memory at sea level on planet Earth in 72 hours is over 95%. Of course that assumes you are using non-error-correcting memory (non-ECC). With ECC, he figured, you can wait 2.7 million years before you get an uncorrectable bit error at a probability of 96%.
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