In the ear ly days of computers, “ glitches” were an accepted w ay of life. Since then, as computers have become more reliable (a nd more relied upon), glitches are no lo nger accep table – yet they still occur. One of the most intractable s ources of glitches has been the transient “bit-flip”, or soft memo ry error: a random event that corrupts the value stored in a memo ry cell without damaging the cell itself. Soft errors in electronic memor y were first traced to alpha particle * missions from chip packa ging materials. Since then, memory manufacturers have eliminated most alpha particle sources from the ir materials, cha nged their designs to make t hem less susceptible (e .g., moved ball-grid bumps farther aw y from memory cells), and even ad ded shielding (usual ly internal die coati ngs). Tests and standards have been developed to meas ure and improve t he resistance of memory chips to alpha particles – but soft errors have not disappeared.
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