Talk:Long mode

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Physical size of 264 bytes[edit]

The article states that "For the time being, it is impractical to equip computers with sufficient memory to require a full 64 bits." This is something of an understatement. Assuming that current (as of 2014) DRAM densities can provide 2×512Mb on a single 12×9mm IC chip, this gives a density of about 9.5 Mbit/mm2 or about 1.2 MB/mm2. Thus 264 bytes would require about 14.8 million square meters of IC real estate (using current technology). Even assuming that we can increase memory densities another 10,000-fold within the next few decades, this would still require about 1,480 m2 of IC space. So I don't see any single CPU ever directly addressing this much total memory space, at least not within my lifetime. — Loadmaster (talk) 22:51, 13 February 2014 (UTC)

Yeah, but slice that 1,480 m2 of IC space into 1 m2 sheets and stack them on top of each other... Let's say that each layer is 2 mm thick – that results in a stack about 3 m high. I'm not saying that's actually going to happen, but from that perspective it might be doable; just remember the old mainframes, which had refrigerator-size boxes as their main components. :) — Dsimic (talk | contribs) 23:01, 13 February 2014 (UTC)
Yes, but those mainframes only had about 224 bytes of physical memory, which were originally in magnetic-core memory form (and which were 3-dimensional stacks of memory planes). But 264 bytes is a vastly larger amount of memory (12 orders of magnitude), and my point is that it is probably too large to actually be contained in a single physical memory unit, at least with IC technology in the foreseeable future. Yes, I expect that 3-dimensional circuits are eventually going to be used to solve the problems of quantum noise, but the reasons it has not yet been successful include the manufacturing cost, failure rates, and enormous heat dissipation problems. — Loadmaster (talk) 19:12, 19 February 2014 (UTC)
Please don't get me wrong, I'm not trying to argue with you, :) but we should remember that many things looked way too big at some point in time – just as 640 KB looked more than enough, probably at some point in time we'll be over even 264 bytes of RAM. — Dsimic (talk | contribs) 19:45, 19 February 2014 (UTC)