The CMOS replaced the illegal NMOS op codes with more useful added instructions and addressing modes, and still leaves some illegal op codes which can be exploited for fast (single-cycle) I/O. But true, if you want to run legacy software that was written for the early NMOS machines using the NMOS illegal op codes, you'll have to use NMOS. I'm rounding up all the NMOS-CMOS differences now to put in a web page. There are lots, both hardware and software.
Soldering gun? Isn't that a bit brutal for working with chips?
Non-native speaker (or writer) mixing up things... does "soldering iron" sound better and less brutal?
Yes. I see "soldering gun" and I visualize the 125 watt one that I use for machinery repair purposes. If I were to use it to solder chips to a PCB it would be akin to swatting flies with a sledge hammer.