When there is a RAM failure, the symptom you see depends on which memory location(s) is/are failing. If the failure is in memory used by the userland, you will see your programs segfault (as you noticed) or misbehave. If the failure is in the kernel, however, you might notice nothing (if the failure corresponds to some rarely used routine, like the code for the kernel;s panic() function, which is only called in case of a panic), you might get kernel panics or strange behavior (if the failure corresponds to code (or critical data, like the page tables)), or you might even fail to boot (if the failure affects the initial steps of loading the bootloader and decompressing the kernel). Note that strange behavior could lead to security compromises; a bit flip in the wrong place could result in security-sensitive code misbehaving.