Chipkill

Article summary

Chipkill is IBM's trademark for a form of advanced error checking and correcting (ECC) computer memory technology that protects memory systems from single memory chip failures and multi-bit errors from any portion of a single memory chip. One simple scheme to perform this function scatters the bits of an ECC word across multiple memory chips, such that the failure of any single memory (SDRAM) chip will affect only one ECC bit per word. If using the typical 72-bit SECDED (single-error correct, double-error detect) Hamming code to approach the problem, the goal would be to scatter each bit onto its own memory chip. This is easily achievable with four ranks of standard x4 ECC DIMM, as each rank has 18 chips. With wider chips or fewer ranks, longer or shorter words will need to be used, either to increase the amount of correctable bits-per-word or to maintain the 1-bit-per-chip scatter. Chipkill is frequently combined with dynamic bit-steering, so that if a chip fails (or has exceeded a threshold of bit errors), another, spare, memory chip is used to replace the failed chip. The concept is similar to that of RAID, which protects against disk failure, except that now the concept is applied to individual memory chips. The technology was developed by the IBM Corporation in the early and mid-1990s.…

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