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TOPIC: Why no 128 bit machines?

Why no 128 bit machines? 1 week 3 days ago #18137

  • JoeV65
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Steve,
Over the years we have seen machines bus speeds increasing from 8 bit to the current 64 bit. Why have we never moved to 128 bit. I remember moving from 32 to 64 and notice a huge gain in performance. Would we not see the same gains or more by moving from 64 to 128? Or have we simply not maxed out 64 bit much like a 3.0 PCIe slot?

JoeV
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Why no 128 bit machines? 1 week 2 days ago #18138

  • i7Baby
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A google search (Tom's and Reddit) reveals that 32 bit meant having addresses for 4GB of data and 64bit would allow for 4 x 4 x gb (billion) x gb (billion) - 16 exabits of addresses. At the moment we're nowhere needing to use so many addresses. If we ever get there, then people will start talking about 128bit machines.
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Why no 128 bit machines? 5 days 3 hours ago #18168

  • Bappy1988
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the word length (number of bits) represents 2 main things; how big of a number you can process (or how precise of a number) in each instruction, and as mentioned already, how much ram you can access.

the big performance boosts we saw when moving to 64bit were because 64bit windows could a) address more than 4gb total system memory and b) allocate more than 2GB ram to a single process.

Programs that used lots of ram previously had to be written so that they didn't load too much stuff into memory at once and therefore there was a lot of hard disk access. 64 bit processors aren't intrinsically faster at processing things that 32 bit processors (some ARM chips are still 32 bit), the fact is they allow more ram to be used and therefore cut back on disk access, thus removing a major performance bottleneck from the rest of the system. Even now, the vast majority of variables assigned in programs are 32 bit values which don't technically require a 64 bit processor to operate over.

I believe the amd64 instruction set allows 56bits to be used to address memory so the practical limit of how much ram you can use is imposed by the capacity of the memory, not the processor's word length.

in some applications (e.g. medical research) the most important factor is the precision of the values being operated upon and in these areas they do indeed use super expensive custom 128bit processors.

In day to day use (even intense gaming) 128 bit word length will provide no benefits at all over 64 bit.
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