Legacy systems and architectures can’t be around forever.
How many people in the PC market still use 16-bit applications?
How many people in the PC market still use 16-bit applications?
Why not? The bits don't decay.. Yes, this leads to an architectural mess, but I'm talking about a competitive business advantage.
> 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%.
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
I’m quite sure we will be OK without support for 16-bit instructions.
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.
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
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?