Oh god yes you need a decent heatsink on that, even if you intend to run with a fan it’ll need to be a fair size to cope with the heat.

I don’t believe I have a Slot 1 CPU of any kind that has anything smaller than about 1.5” thick.

duboisea wrote on 2023-07-10, 16:09:

I just purchased this CPU and not sure if I need an additional heatsink/fan.

Are the holes/grooves to attach something or to dissipate heat?

Oh you 100% need one !

Some low freq. Pentium II (< ~300 Mhz) can be passively cooled, but even then, the cooler is massive and requires a good airflow in the case.
The 450 is the top frequency available for the Pentium II, so heating is definitely higher.

You can either find the original cooler (or scavenge one on a less desirable PII) or you can find aftermarket ones.
You can even find new old stock sometimes (https://www.pearl.fr/article/JC11/ventilateur-p22a)
Be sure to check compatibility because i think there are different models that may be incompatibles with some cpus.

Joining the chorus, yes, you definitely need that.

Happened to have a semi passively cooled 400MHz Deschutes PII close at hand, here's what it looks like:

Note semi passively cooled. It sat very close to the exhausting case fan in the computer it came from, assuming the airflow around it was more than negligible. Should give you an idea.

Op has a SECC1 cart and will need a SECC1 cooler, there is also a SECC2 cart used on the later PII 400/450 and PIII carts.

SECC2 can be identified by the 4 holes that go through the package, the two cooler types are not interchangeable.

@duboisea
You need SECC1 cooler with hooks to attach to plate.

acl wrote on 2023-07-10, 19:44:

Some low freq. Pentium II (< ~300 Mhz) can be passively cooled, but even then, the cooler is massive and requires a good airflow in the case.

Only recommendet for the later produced Pentium II 266/300 CPUs with 250 nm Deschutes core (~18,6W TDP). I would not do this with the older 350 nm Klamath based Pentium II cores...the 300MHz Klamath for example has a TDP of 43W! So about ~50% less heat between this two cores with the same frequencys.