There's plenty of foundries cheaply fabbing chips in "obsolete" process nodes. If the original design from 25+ years ago is available, there's no reason why it couldn't be fabbed today in those quantities.
Generally old chips are good, depends on the purpose. Some things like the f35 would like to use TSMC’s fabs. But not every chip is for only processing and larger process have their advantages for certain applications like power, analog, and em hardening
Why can't they just make pin-compatible versions of the chips using new processes? That would take time, but surely easier than investing in new fabs for old processes?
That's a naive statement that presumes the design used today is mostly similar to the 40 year old design.
Even if it was the exact same circuit design, that's only a small part of what makes a processor and negates all of the advancements in chemistry, lithography, engineering, and everything thing else that goes into manufacturing a chip.
It's like saying "why are we still using scissors|staplers|brushed electric motors|internal combustion engines?"
Think of all the chips from then and before then that are becoming rare. The hobbyist and archivist community do their best with modern replacements, keeping legacy parts alive, and things like FPGAs, but to be able to fab modern drop in replacements for rare chips would be amazing.
Things don't have to be ultra modern to offer value.
We already have chips that we're not really able to reproduce, like some of the custom chips and ULA (Uncommitted Logic Array) in older micro computers. The fabs and technology is abandoned, and while we might be able to recreate it the results might not be completely identical chips.
Not at all obsolete, defect rates rise exponentially as you increase die sizes, so wafer scale chips are stupid and wrong, but in financial sense only.
If you’re paying up for an entire batch and you only need one working example out of it, it probably matter less.
Modern chips sure, but what about chips from a few generations ago? Do the factories they made 20 years ago for what was then cutting-edge tech still exist and produce things using that era of chip making tech, or have they been modernized?
Not exactly. If you have a 5nm fab you can produce chips today that you know work. (the yield might be terrible, but you can get some functional chips every day). In February what we had was something that completed the process, but we had no idea if it worked at all.
It's embarrassing that manufacturers are still making computers with silicon chips in them. The first silicon chip was over 50 years ago. Yes, most of the components and surrounding systems have been upgraded, but it still has the same basic material.
(etc., etc. -- "old" does not mean "bad"; the 757 is a perennial example of people claiming to want something they don't really want; and the 737 is a proven, successful design, so there's absolutely no "embarrassment" in the fact that it's still being manufactured and flown)
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