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In this paper, we introduce unequal-error-protection error correcting codes (UEPECCs) to improve SRAM reliability at low supply voltages for mobile multimedia applications. The fundamental premise for our work is that in multimedia applications, different bits in the same SRAM word are usually not equally significant, and hence deserve different protection levels. The key innovation in our work includes (i) a novel metric, word mean squared error, to measure the reliability of a SRAM word when different bits are not equally significant and (ii) an optimization algorithm based on dynamic programming to construct the UEPECC that assigns different protection levels to bits according to their significance. The advantage of the UEPECC over the traditional equal-error-protection ECC is demonstrated using two representative multimedia applications. For the same area, power, and encoding/decoding latency, SRAMs with UEPECC increase the peak signal-to-noise ratio by 8 dB in image processing and incur 60% less errors on average in optical flow (motion vector) computation.