I was curious about why there was a solenoid in the keyboard since the only mechanical part should be the actual key switches. Apparently the purpose of it was

I was curious about why there was a solenoid in the keyboard since the only mechanical part should be the actual key switches. Apparently the purpose of it was to have an audible cue for when a key press was accepted. No solenoid click means your key presses aren't going through either because the machine is busy or some other issue. It's a neat skeuomorphic feature since everyone using this keyboard at the time it came out would have been familiar with electric typewriters and the sound they make. Since electric typewriters have the same ability to block key presses when it's not ready for input (like during a carriage return), there would have been the same recognition that the terminal wasn't ready. I can't imagine trying to hear my own thoughts in an office filled with these things clacking away like it's a 1940s typing pool. I'm not familiar enough with IBM terminals to know but I'm sure it didn't take long for them to switch over to a much quieter operation as businesses began to purchase more of these. There's a reason why we have moved from loud keyboards to nearly silent ones other than just cost.