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The architectural vulnerability factor (AVF) of a hardware structure is the probability that a fault in the structure will affect the output of a program. AVF captures both microarchitectural and architectural fault masking effects; therefore, AVF measurements cannot generate insight into the vulnerability of software independent of hardware. To evaluate the behavior of software in the presence of hardware faults, we must isolate the software-dependent (architecture-level masking) portion of AVF from the hardware-dependent (microarchitecture-level masking) portion, providing a quantitative basis to make reliability decisions about software independent of hardware. In this work, we demonstrate that the new program vulnerability factor (PVF) metric provides such a basis: PVF captures the architecture-level fault masking inherent in a program, allowing software designers to make quantitative statements about a program's tolerance to soft errors. PVF can also explain the AVF behavior of a program when executed on hardware; PVF captures the workload-driven changes in AVF for all structures. Finally, we demonstrate two practical uses for PVF: choosing algorithms and compiler optimizations to reduce a program's failure rate.