at first I thought you were talking about people who were fans of computers :)

There may be many reasons, but to start with, were older fans more noisy? So far this question is neither focused nor anything but personal opinion. Or could improve it by adding substantial data?

Once offices and domestic living spaces filled up with computers, people really needed them to be quieter - so change happened. 120mm and 140mm fans are common now, and can move lots of air at low fan speeds. Servers, on the other hand, are stuck in 1U or 2U racks and can't have anything bigger than tiny little 40mm fan cannons that spin at absurd speeds (like 12,000rpm) to move enough air - and those are still LOUD, even today. Like 60dBA loud.

Well, most of my old (non-PC) computers are "sans-fans".

I understand now why people put liquid cooling in their rigs. 4k with HDR at 60fps on 12 processors at 4Ghz, I might as well be launching space shuttles. You're just not pushing your hardware to its absolute limit, and it probably wasn't designed to be.

CPUs also acquired thermal throttling and throttling in general, so they do not run at full speed all the time.

The original Mac didn't even have a fan. They just designed it so that passive air flow was enough. IIRC there was a grille in the top and also down at the bottom, and it would set up a flow of air just like a fireplace.

A part of the reason is that in the past 20 years you have lost a lot of hearing ability! You have likely lost at least 10 dB, more if you have been exposed to harmful noise...

@Nelson processors at that time consumed only a few watts anyway, so there wasn't much to save with thermal throttling

The answers mostly focus on fans, and fans as part of a system, but also the chips are now much smaller, and presumably require less heat-sinking than they used to.

@JosephDoggie smaller, denser (i.e. with more transistors per unit of area) chips require more cooling assistance, not less.

@JosephDoggie not really true. The different 486 CPUs had TDPs between 4 and 9 watts (about 10% of the CPUs found in current PCs). Around the year 2000 I was working on a medical device that was built around 486, because at the time it was the fastest CPU that could do without heatsink (it was important, because heatsink or any kind of holes would make it impossible to disinfect the case)

I stand corrected. Well, it dispels one theory, anyway.

BTW, how do you know that the fan is the noisy part? Back in the day hard drives often had a loud buzzing or grinding sound when they were just spinning idle. And of course they were bolted directly to the chassis without any insulation.

@Jean-FrançoisFabre Now that you mention it, I always wondered if using the term ‘fan’ for people originated in a simile to, like, those slaves you see in drama films set in ancient Egypt or whatever that wave fans at the pharaoh to cool them off, as in being so devoted to someone else you might as well be their literal fan-waving servant

@user3840170 It's believed to have been shortened from "fanatic".

The question is really backwards: loud fans were what we had back then. It's those loud fans (among other things) that motivated research in how to make quieter fans, and quieter PC cooling systems.

My own custom-built 486 in 93 was as silent as my current machine is (excluding the harddisk noise) - back then, silent fans were available, of course, but rare.

I believe you got it backwards. Industrial fans are pretty much as loud as they were, and computer fans were just industrial fans. Real question is what caused modern computer fans to be quiet.

@Haukinger: But of course your 486 in '93 was more than a decade into the noisy computer era. While I never found a quiet fan back then, I was lining cases with sound-deading material and putting machines inside larger wooden cabinets to try to mute the noise.