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How testing influences which name appears on your module.
Sure, testing is important. But does it really matter what will happen to your memory at 200° F when it's a comfortable 70° F in your house? Actually ... it does.
Even though it's 70° F in your house, the chips inside your system get a lot hotter. One common cause is a spike in power that reaches your PC (a good reason to use a surge protector). Also, any normal computer use will cause the parts inside your PC to heat up. Basically, your computer may see conditions that are more extreme than what you see in front of the monitor. For this reason, major DRAM manufacturers use what's called guardbands in their testing.
It's a pretty simple concept really, kind of like insurance. A guardband helps to ensure that a chip will work properly, even under many abnormal operating conditions. For example, let's say a chip needs to meet a particular parameter between 10 and 20 to be acceptable. Rather than set the test to fail anything less than 10 or greater than 20, the test is set to fail anything less than 11 or greater than 19. Yes, more failures occur this way, but these additional failed parts are close enough to the limits to imply some sort of process variation. It's not worth the risk to the chip manufacturer to ship these parts to customers under their brand name.
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After going through this extensive series of tests, you can be confident that the passing parts will work for a long time.
So what happens to the parts that failed testing? Some get thrown out, but many are re-tested and graded to lesser speeds and/or conditions (i.e. without guardbands). Others aren't even re-tested (even though they might not have gone through burn-in). Yes, these lower-grade modules will probably work today, but they're more prone to marginal performance and failures, especially over time. DRAM manufacturers often sell this memory to third party vendors who then re-label them with their own brand name. Third party vendors are often required to remove the original DRAM manufacturer's name from the chips. This memory is typically referred to as "generic memory."
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