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Memory scrubbing
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<p>Memory scrubbing consists of reading from each <a href="/facts/Computer_memory/hQKVQ51J">computer memory</a> location, correcting <a href="/facts/Bit_error/ovAAPFjV">bit errors</a> (if any) with an error-correcting code (<a href="/facts/Error_detection_and_correction/o2rH8e3n">ECC</a>), and writing the corrected data back to the same location. </p><p>Due to the high integration density of modern computer memory <a href="/facts/Integrated_circuit/fjn6vg7C">chips</a>, the individual memory cell structures became small enough to be vulnerable to <a href="/facts/Cosmic_ray/uxCVdTKd">cosmic rays</a> and/or <a href="/facts/Alpha_particle/dzNMs9WP">alpha particle</a> emission. The errors caused by these phenomena are called <a href="/facts/Soft_error/E77QBbqI">soft errors</a>. Over 8% of dual in-line memory modules (<a href="/facts/DIMM/Ejh7lpxq">DIMMs</a>) experience at least one correctable error per year. This can be a problem for <a href="/facts/Dynamic_random-access_memory/koI9FGo5">DRAM</a> and <a href="/facts/Static_random-access_memory/Pmyo4V5e">SRAM</a> based memories. The probability of a soft error at any individual memory bit is very small. However, together with the large amount of memory modern computers—especially <a href="/facts/Server_(computing)/dEaYFD7r">servers</a>—are equipped with, and together with extended periods of <a href="/facts/Uptime/7PXQlwEE">uptime</a>, the probability of soft errors in the total memory installed is significant. </p><p>The information in an <a href="/facts/ECC_memory/eG38xJoR">ECC memory</a> is stored <a href="/facts/Redundancy_(information_theory)/HnbfBLE0">redundantly</a> enough to correct single bit error per memory word. Hence, an ECC memory can support the scrubbing of the memory content. Namely, if the <a href="/facts/Memory_controller/tHq2zlws">memory controller</a> scans systematically through the memory, the single bit errors can be detected, the erroneous bit can be determined using the ECC <a href="/facts/Error_detection_and_correction/o2rH8e3n">checksum</a>, and the corrected data can be written back to the memory. </p>