Re: Humidity control
As a young lad* I was taken around Daddy's offices. Daddy wrote operating systems for IBM mainframes, and the computers** were kept in a custom built glass cube on the side of the Georgian mansion they'd bought as offices. In addition to the aircon, Halon systems etc I clearly remember being told about how we had to go through an airlock because they also maintained an artificial air pressure differential between the computer room and the outside world. So no, not really just "a room with computers".
*Some decades. Shoulder pads were in, as was (just) Margaret Thatcher. Still hadn't heard of the Falklands though.
*I was 8. I don't remember model numbers etc. They were big boxes with glass lids.