that's the heatspreader, not the heatsink. Every pentium need AT LEAST a heatsink to function properly. These aren't made anymore I suppose, but you can fit socket 370 and socket A coolers on these if you want.

Heatspreader just transfers the heat better to a heatsink? What is the purpose of it apart from looking cool? 😀

The answer is in your question ^^

Well, it is called heatspreader... It's just weird that Pentium 75 and 90 had it, but 100 and above didn't (afaik there are Pentium 100 CPUs with golden heatspreders but these are rather rare).

Same goes with socket 4 pentiums, some have a golden heat spreader and others don't for some reasons.

I was always curious about why the Socket4 and Socket5 Pentiums sometimes had gold caps. I think intel made *some* 8086s and 8087s with gold caps, but for about 10 years they didn't make any x86 CPUs with gold caps until the Pentium showed up. Did the gold cap CPUs have improved thermal characteristics over the regular CPGA chips?

Well the Pentium that didn't have any gold IHS (nowadays it's aluminium or copper ? Correct me if I am wrong) had a ceramic IHS

But it (ceramic) wasn't that effective at spreading the heat, so they went back to metal heat spreaders.

At one time they went with DoD cooling (the CPU's die being out in the open and making direct contact with the heatsink) it was very effective but that was rather risky as if you either screwed up the heatsink mounting, you could crush the die.

So they went back to copper (according to some Intel datasheets, they use nickel-plated copper heatspreaders) spreaders, some had the die soldered to the die some had thermal paste in-between (the CPUs that had a metallic IHS and paste in between the die could be "delidded" to either convert them to DoD or repast the die but since Intel switched back to soldered IHSes it's no longer possible)

AMD for the other part, I belive they went DoD with the socket A Athlons and derivates but they used since soldered heat spreaders (exception of some Athlon 64 chips)

I think it's copper coated with aluminium or something like that

That would be likely since Copper is one of the best conducting metals (both thermally and electrically) but yeah aluminium isn't far off copper at all in terms of thermal conductivity.

Edit: yep Intel does indeed use copper to make IHSes (specifically, nickel-plated copper)

Cooling has always been a tug of war between how much heat is the CPU generating and how much heat is the cooling systems removing.

The P75 was something like 8W and was sold around the time high end 486 CPUs were still popular and use little shitty heatsinks and fans. Engineers had to assume that OEMs would be using passive heatsinks or low profile ones with small fans like the 486 had and went with better tops. After a while the Pentium line doubled to 16W but by then there were much larger heatsinks with better fans out there to get rid of the heat and those expensive metal lids were no longer needed.

Anything newer than Intel 486dx2-66 require heatsink that are large, or a small heatsink and a fan.

Its an artifact of early packaging processes deficiencies
that top gold colored plate is there only to help spread the heat, actual CPU die is mounted from the bottom
ceramic cpus are popular with scrappers due to heavy gold plating (maybe even gold bond wires in early models)
later MMX packages moved to flip chip with laminate (pretty much a specialized PCB) carrier and metal heat spreader actually touching the die
Coppermine same deal, but thicker silicon and no spreader
AMD also went flip chip no spreader, but used thinner fragile die package = lots of tears over cracked silicon