5 ms·

Legacy systems and architectures can’t be around forever. How many people in the PC market still use 16-bit applications?

jhallenworld 3y ago
>Legacy systems and architectures can’t be around forever. Why not? The bits don't decay.. Yes, this leads to an architectural mess, but I'm talking about a competitive business advantage.
- manuelabeledo 3y ago
  > Why not? > Yes, this leads to an architectural mess Right there. There's no notable advantage in supporting a very small minority of the applications out there, at the cost of keeping units useless for the 99%.
  - bear8642 3y ago
    > There's no notable advantage... Potentially one if a large customer's paying you for it. At work, I'm helping a client upgrade from a decade old version (v12) of our product and having to copy over the switches to keep the even older (v11 and previous) behaviours
    - manuelabeledo 3y ago
      Ten years ago was 14 years after the introduction of the x86 64-bit instruction set, and 28 years after x86-32. I’m quite sure we will be OK without support for 16-bit instructions.
MrBuddyCasino 3y ago
Question is, what is the cost of keeping the old cruft around?
- userbinator 3y ago
  Essentially none. It's all make-work (or, since they're intent on breaking things more than fixing them, break-work.)
  - manuelabeledo 3y ago
    I wouldn’t say “none”. Real estate in CPUs is extremely expensive.
    - akira2501 3y ago
      My immediate sense is that the entire vector system easily dwarfs the 16bit system.. as I'm guessing most of the modern 16bit mode is entirely in microcode.
    - userbinator 3y ago
      ...and taken up mostly by cache and vector execution units. An 8086 has 29000 transistors. A modern CPU has several billion. The amount needed to implement the 16-bit subset of the ISA is an absolutely tiny fraction of the total area.
      - FullyFunctional 3y ago
        Ah, I see you don't work in the field. A few of the cost of legacy: * exponential growth in verification space (each feature combines with all other features), * design complexity (effort that could be spent better), * area/power/cycle time overhead (all options require more ports to muxes, more wires to run, etc.) * and most importantly, opportunity costs: some optimization tricks can't be pursued because the assumptions would break for legacy code The legacy tax is real
        userbinator 3y ago
        Ah, I see you don't work in the field. I won't give away too much of my personal history, but it suffices to say I've worked with x86 at the hardware level before. each feature combines with all other features They do, but orthogonally. effort that could be spent better Effort that has already been spent. all options require more ports to muxes, more wires to run, etc It's all ultimately split into uops anyway. some optimization tricks can't be pursued because the assumptions would break for legacy code What assumptions in particular?

jhallenworld 3y ago

>Legacy systems and architectures can’t be around forever. Why not? The bits don't decay.. Yes, this leads to an architectural mess, but I'm talking about a competitive business advantage.

manuelabeledo 3y ago
> Why not? > Yes, this leads to an architectural mess Right there. There's no notable advantage in supporting a very small minority of the applications out there, at the cost of keeping units useless for the 99%.
- bear8642 3y ago
  > There's no notable advantage... Potentially one if a large customer's paying you for it. At work, I'm helping a client upgrade from a decade old version (v12) of our product and having to copy over the switches to keep the even older (v11 and previous) behaviours
  - manuelabeledo 3y ago
    Ten years ago was 14 years after the introduction of the x86 64-bit instruction set, and 28 years after x86-32. I’m quite sure we will be OK without support for 16-bit instructions.

MrBuddyCasino 3y ago

Question is, what is the cost of keeping the old cruft around?

userbinator 3y ago
Essentially none. It's all make-work (or, since they're intent on breaking things more than fixing them, break-work.)
- manuelabeledo 3y ago
  I wouldn’t say “none”. Real estate in CPUs is extremely expensive.
  - akira2501 3y ago
    My immediate sense is that the entire vector system easily dwarfs the 16bit system.. as I'm guessing most of the modern 16bit mode is entirely in microcode.
  - userbinator 3y ago
    ...and taken up mostly by cache and vector execution units. An 8086 has 29000 transistors. A modern CPU has several billion. The amount needed to implement the 16-bit subset of the ISA is an absolutely tiny fraction of the total area.
    - FullyFunctional 3y ago
      Ah, I see you don't work in the field. A few of the cost of legacy: * exponential growth in verification space (each feature combines with all other features), * design complexity (effort that could be spent better), * area/power/cycle time overhead (all options require more ports to muxes, more wires to run, etc.) * and most importantly, opportunity costs: some optimization tricks can't be pursued because the assumptions would break for legacy code The legacy tax is real
      - userbinator 3y ago
        Ah, I see you don't work in the field. I won't give away too much of my personal history, but it suffices to say I've worked with x86 at the hardware level before. each feature combines with all other features They do, but orthogonally. effort that could be spent better Effort that has already been spent. all options require more ports to muxes, more wires to run, etc It's all ultimately split into uops anyway. some optimization tricks can't be pursued because the assumptions would break for legacy code What assumptions in particular?