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Why we don't have 128-bit CPUs (www.xda-developers.com)
submitted 2 months ago by jwr1@kbin.earth to c/technology@lemmy.world
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[-] ulterno@lemmy.kde.social 0 points 2 months ago

RV64 has a maximum 32-bit instruction encoding

I kinda expected that to happen, since there's already enough to fit all required functions. So yeah, even this is not a good enough criteria for bit rating.

those original 8-bit intructions still exist, and take up a huge part of the encoding space, cutting the number of n-bit instructions to more like 2^(n-7)

err... they are still instructions, right? And they are implemented. I don't see why you would negate that from the number of instructions.

[-] wewbull@feddit.uk 2 points 2 months ago

If the 8088 had used all but one 256 8-bit values as legal instructions, all your new instructions after that point would need to start with that unused value and then you can add a maximum of 256 instructions by using the next byte. End result is 511 instructions can be encoded in 16-bits.

[-] ulterno@lemmy.kde.social 0 points 2 months ago

Ah right! I forgot about that.

So you either have to pad all instructions in all previous binaries, or reduce the amount of available instructions in the arch update.

this post was submitted on 23 Jun 2024
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