4 ms·

Someone said that about 64 bits.

• mikeash 10y ago
  And 32 bits! Probably 16 bits too.... But, it takes longer each time. With exponential growth (e.g. Moore's Law) then you use up bits linearly. If you double every two years, then you use one bit every two years. That means we have about 32 years from when 32-bit became inadequate to when 64-bit becomes inadequate.
  • _ph_ 10y ago
    And with Moores Law running out of steam (isn't physics a bitch!) this might not even ever happen. At least not in the sense which drove us up to 64 bit. There are of course plenty of reasons why we would like to do math with 128 or more bits, but for memory addresses, 64 bit are a plenty.
    • Dylan16807 10y ago
      64 bits are fine until you want to share address space over a whole bunch of nodes. We currently have supercomputers with tens of gigabytes per processor and tens of thousands of processors. Already up to 51 bits. We're also working out fast persistent storage like NVMe and crosspoint that allow us to attach a board with terabytes where we used to attach gigabytes of DRAM. Combine those two and you can max out a 64 bit address space with current technology, let alone tomorrow's technology.
      • LukeShu 10y ago
        Remember that each bit doubles the space. You would need 50,000 processors with 350 terabytes of memory each to hit 64 bits. Then again, super computers aren't really running the same architecture as the rest of us.
        • Dylan16807 10y ago
          So let's crunch the numbers a bit. There are already supercomputers with 40k CPUs, let's go all out and plan to use 80k CPUs. 8TB NVMe cards have been out for a couple years, we should be able to get 16TB cards by the time we're assembling. We should be able to fit four per CPU with a compact design. That gets us to 5EB. That's dangerously close to the 16EB limit, and that's with 2016/2017 technology. And the point where you start having trouble isn't 16EB, it's under 8EB, when you stop being able to use the normal user/kernel split or have all the memory mapped into kernel space. > Then again, super computers aren't really running the same architecture as the rest of us. Sure, but there are pushes to make datacenters act more like a giant computer, so there are niceties to a shared address space that aren't restricted to traditional supercomputers.
        • gaius 10y ago
          You say that but SSI is bound to become fashionable again at some point.