Back in the day IBM offered two versions of their mainframe. One slower and much less expensive.
People would buy the slower ones and often discover that they were too slow.
But for a chunk of cash they would upgrade the slow mainframe to the fast model.
A tech would swap out identical boards with different part numbers, install a version of the OS without wait states, and flip a well concealed switch to speed up the CPU.
The fellow I learned this story from had been an IBM tech who used to flip the concealed switch on slow machines without being paid to. He said other techs would often flip it back.
Reminds me of one of my first PCs that had a “Turbo Boost” button on the front with a little light that went on and was supposed to speed your CPU up to 11 mhz or something. Of course as soon as we unboxed the thing, we pressed that button and left it on forever!