SoC 101 - Lecture 6a: The Memory Hierarchy

[@abhisheksoni1544]

Thank you sir for these lectures ❤

[@AdiTeman]

It's my pleasure

[@igorfomin2570]

I wonder whether NVMe drives change this picture a little bit. After all, these drives operate faster than SATA or IDE drives.

[@AdiTeman]

That's a great point. We have been waiting for quite some time for "storage class memory" to disrupt the traditional memory hierarchy. The first real options we have out there are the PCM-based Optane drives. They are supposed to provide a median level between the DRAM and SSD. But they haven't caught on yet, as much as they were expected to, and haven't really caused a disruption. They also aren't really different, but rather a faster secondary storage, if I understand correctly. There are other options that are either already out there in the wild or "coming soon" (I put that in quotes, since it's been over 15 years that they've been "coming soon"). There are many types of emerging technologies, such as MRAM, ReRAM, etc., which will (maybe?) one day provide a true additional level of the hierarchy and maybe one of these technologies will actually make one or more of the existing ones redundant. But that has yet to happen. Let me tell you that the magnetic hard drive has been pronounced dead for probably 30 years. And yet, they still sell a ton of magnetic hard drives today. Same with Flash... So don't write off DRAM or SSD just yet :)

[@igorfomin2570]

Thank you for the answer, professor! For hard drives, I think the main reason may be the duration of storage. After all, modern SSDs use TLC and QLC as their basic element. And those cells loose charge. At least, as I know. Has no such problem for HDD. Seems like a no replacement so far. I even heard that some people still prefer use magnetic tapes for the long-time storage. Seems exotic to me. But at least Tape Archive (tar) may be used as intended. :) Oh, but there are also optical drives which seemingly did disappear, didn't they?

[@AdiTeman]

@@igorfomin2570 Yes, I guess this is one of the reasons. Historically, I think the reason for the persistence of the magnetic drives is the price, but as SSDs get cheaper, it could be that some people would prefer to have magnetic or tape archives. That said the durability of flash (including SSD, etc.) is due to writes, so there shouldn't be a problem with long term storage. Yes, I believe optical drives are not too popular these days...