I could geeze all day, like the geezer I am, with stories about the good old days :-)
In school, your programming exercises are well-defined, small, and can be completed in a few days. First day of my internship with Intel: "Here is a 50,000-line program somebody has been working on for 8 months. But it's too slow, we need to you speed it up by 10x before the summer ends." LMAO. But I figured out how to do even better than that. The routing graph was implemented using pointers from one node to another. But the grid was rectilinear and not very sparse so I could just use a 2d-array to store the graph. Improved memory, improved cache utilization--it ran 2,000 times faster :-) I got a divisional award and so many stock options I was able to buy a house and a brand-new porsche 911 a few years later.
Imagine your job is to solve an NP-hard problem. Like placing the cells on a chip, or routing the chip. The runtime grows exponentially with your problem size....
...and your problem size doubles every two years :-) Every two years, all your data structures, all your algorithms, have to be revamped so that they can handle twice as much data. We used to call it "Even More's Law" :-)
As far as what tools we used, back then Intel mostly used in-house designed tools. They were not very friendly to newbs, they were built for power users. Hard to use, cryptic commands. Hyper customized to Intel's design flows. Could not be used at any other company.
Every year it became harder and harder to compete with outside vendors like Cadence and Synopsis. Eventually, the era of chip companies making their own EDA tools ended. It was fun until it ended.
The best part, though, was it was the 90's. The iron curtain had fallen, we were friends with Russia and the east block :-) Bill Clinton had eliminated the budget deficit, so borrowing costs were very low, and businesses could expand. The whole dot com thing was going on, and everybody was making more money than they could count.
Then...the supreme court puts George W in office. We spent $3 trillion on oil wars, for false reasons, and for which we got nothing in return. Sure did piss off all of our new friends like Russia, though.
Record surpluses went to record deficits. Interest rates rose, and the entire world economy just collapsed in 2008. Which was right around when this year's high-school graduates were born....nobody has seen what the economy should be like for over a generation now.