Maybe you could achieve this by undervolting the CPU ?

I ran a pentium MMX 200 at 2.5V instead of 2.8 (and I even overclocked it to 225 and 233MHz) and it was rock stable. I should try it on my super socket 7 to see how far I can go into undervolting

However be careful because it makes the regulator heat more if it's not designed for "high power" CPUs

Also some PCs were sold with no fan at all.
My IBM PC 340 has a pentium 100 and there was no fan on the radiator and neither anywhere in the computer (except for the PSU for obvious reasons)

A Pentium 75 is able to run without heatsink without crashing (although the intense heat doesn't do it good). With a big heatsink it wouldn't be a problem to run Pentiums without active cooling. In Compaq systems (fitted with Pentium 75 ~ 100) I found heatsinks like these (not actual picture, but similar). I'm sure these will run fine on a Pentium 133 as well.

Thanks for the info. Starting from the late 486 era I've only seen active cooling, except for some special systems. A Pentium in the 75 ~100 range is fast enough, it's going to be a DOS/WIN31 system.

Currently got a Cyrix MediaGXM system which is fanless, but I need more ISA slots.

I recieved a P166 system once, that had a passive cooling.
This was more or less a giant heatsink with a lot of ribs.

If you can find something like that, it can be attached and used without problems.
You only need to have some air moving inside the case.

I don't see why not. Down-clocking and under volting will likely lead to amazing reduction in heat. For example take a 1.6 V K6-III+ and run it at 66x2 = 133 MHz and that chip will just casually sip energy 😀

i've seen lots of passively cooled non-MMX pentiums. I just got a full socket 5 system with a Pentium 133 that was passively cooled.

Ive been running a Pentium 166 MMX for about 3 weeks now with only passive cooling at regular voltage. To compensate I'm using a 100mm case fan mounted on the side panel of the case (modern ATX case), about 3 inches above the cpu with 80mm exhaust fan 2 inches to the side. Seems to run cool enough, and it pretty much eliminates the noise so I'm thinking of keeping the setup this way. This probably won't work well with a period accurate case unless you want to take a drill to it though. 😵

A P75 has an 8 watt TDP, double that of a 486DX which often runs with no heatsink. Attaching /some/ heatsink will probably be enough, a large one with something else driving air through the case will be enough for safety.

SRQ wrote:

486DX which often runs with no heatsink

In my case, I have glued a chipset cooler onto my dx33. Not that a stock dx33 runs cold or anything, it actually runs pretty warm.
Shure I could run without, I just feel the need to add one "just in case" I need to crunch big numbers or something like that.

I've seeI've seen loads of socket 7 machines with no fan. Slot 1 machines too. Some dell socket 5 and 7 machines run fanless - with CPU's under 133MHz - over that they use a case fan that blows into the CPU heatsink. Compaq runs the Deskpro 1000 w/o a CPU fan as high up as a Pentium II 266. Faster chips use a fan tough.

If you plan to run a Pentium 233 w/o a cpu fan, you will need a big-ass heatsink (think socket A size or bigger) and a quiet case fan to blow on it from a distance. Don't try running a fast K6-2 or K6-3 w/o a fan. I tried it with my 1.6v K6-III+ 400ADZ and it stayed cool for the first 30 mins. After an hour of playing NFS Porsche, the machine froze. When I opened it up the massive heatsink I put on it was extremely hot.

My Original Pentium 133 system had no heatsink attached when I got it, ran it for 2 years that way not a single crash

Years ago I had a Pentium 200 that ran on a large passive heatsink. Don't remember the unit it came out of, but I was surprised to find that to say the least. Still have the heatinsk today.

I once saw a Dell Dimension XPS P75; the CPU had a small fanless heatsink on it, but attached the front panel was a ~60mm fan that blew air across it (and the rest of the motherboard).

candle_86 wrote:

My Original Pentium 133 system had no heatsink attached when I got it, ran it for 2 years that way not a single crash

Yea - well it's a 133mhz pentium, not a 400mhz k6-3. Fast socket 7 chips need active cooling or at least a huge heatsink and good case ventilation.

I once salvaged a non-MMX Pentium 200 from a Gateway 2000 PC, it used a green heatsink without a fan, not much larger than your regular Socket 7 heatsink. There wasn't a single fan in that machine, even the power supply was passively cooled. I still keep that CPU, motherboard (a Gateway version of Intel's LT430TX), memory and the hard drive (Quantum Fireball 3.2Gb).

You also have the option of a IDT Winchip C6, even at 200MHz those don't need a fan, probably be just fine without a heatsink altogether even!

I've got a 400MHz pentium 2 that is fanless. I even managed to overclock it at 450 without adding anything and I don't have any problems with stability with that cpu. I also have a 350 MHz pentium 2 from Compaq wich has a very tall aluminium heatsink

It sounds like I have plenty of options. I assume that in most cases a case fan is present? My current system is completely fanless, which is kinda neat and what I want for the new build, if possible. I'm going to compare and read about all of your suggestions.

If noise is the main reason for running fanless, HDD is one of biggest noise makers.
Go Solidstate or SD card IDE controller for totally silent system (and much faster).