5 ms·

> filling out a 64 bit address space looks tough. I struggled to find something of the same magnitude of 2^64 and I got ‘number of iron atoms in an iron filing’

by lloeki 4y ago

> filling out a 64 bit address space looks tough. I struggled to find something of the same magnitude of 2^64 and I got ‘number of iron atoms in an iron filing’ Reminded me of Jeff Bonwick's answer to the following question about his 'boiling the oceans' quip related to ZFS being a "128 bit filesystem": > 64 bits would have been plenty ... but then you can't talk out of your ass about boiling oceans then, can you? Sadly his Sun hosted blog was eaten by the migration to Oracle, so thanks to the Internet Archive again: http://web.archive.org/web/20061111054630/http://blogs.sun.com/bonwick/date/20040925 http://web.archive.org/web/20061111054630/http://blogs.sun.c... That one dives into some of the "handwaving" a bit: https://hbfs.wordpress.com/2009/02/10/to-boil-the-oceans/ https://hbfs.wordpress.com/2009/02/10/to-boil-the-oceans/ And that one goes into how much energy it would take to merely spin enough disks up: https://www.reddit.com/r/DataHoarder/comments/71p8x4/reaching_the_limit_from_zfs/ https://www.reddit.com/r/DataHoarder/comments/71p8x4/reachin...

PaulHoule 4y ago
One absolute limit of computation is that it takes (1/2) kT of energy to delete one bit of information where k is the Boltzmann constant and T is the temperature. Let T = 300° K (room temperature) I multiplied that by 2¹²⁸, and got 1.41×10¹⁸ J of energy. 1 ton of TNT is 4.2×10¹² J, so that is a 335 kiloton explosion worth of energy just to boot. That's not impossible, that much heat is extracted from a nuclear reactor in a few months. If you want to go faster you need a bigger system, but a bigger system will be slower because of light speed latency. (You do better, however, at a lower temperature, say 1° K but heat extraction gets more difficult at lower temperatures and you spend energy on refrigeration unless you wait long enough for the Universe to grow colder.)
- turtletontine 4y ago
  In fairness, the need for 128-bit addressable systems will be when 64 address bits is not enough. That will be long before people are using 2^128 bytes on one system. So doing the calculation with 2^65 bytes would be a more even handed estimate of the machine that would require this
- tuatoru 4y ago
  > 1.41×10¹⁸ J of energy. Used over the course of a year, that is a constant 44.4 GW. Less than Bitcoin uses already

by lloeki 4y ago

PaulHoule 4y ago

One absolute limit of computation is that it takes (1/2) kT of energy to delete one bit of information where k is the Boltzmann constant and T is the temperature. Let T = 300° K (room temperature) I multiplied that by 2¹²⁸, and got 1.41×10¹⁸ J of energy. 1 ton of TNT is 4.2×10¹² J, so that is a 335 kiloton explosion worth of energy just to boot. That's not impossible, that much heat is extracted from a nuclear reactor in a few months. If you want to go faster you need a bigger system, but a bigger system will be slower because of light speed latency. (You do better, however, at a lower temperature, say 1° K but heat extraction gets more difficult at lower temperatures and you spend energy on refrigeration unless you wait long enough for the Universe to grow colder.)

turtletontine 4y ago
In fairness, the need for 128-bit addressable systems will be when 64 address bits is not enough. That will be long before people are using 2^128 bytes on one system. So doing the calculation with 2^65 bytes would be a more even handed estimate of the machine that would require this
tuatoru 4y ago
> 1.41×10¹⁸ J of energy. Used over the course of a year, that is a constant 44.4 GW. Less than Bitcoin uses already