This graph charts the sensitivity of a 256-megabit synchronous dynamic random-access memory (SDRAM) to heavy ions at 4.5 MeV per nucleon. The testing regimen looked for single-event upsets (SEU), single-event functional interrupts (SEFI), and stuck-bit effects. SEFI included errors to a patch in the memory, errors to consecutive address locations, and errors accompanying an increase in bias current.