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Comment by pingyong | Hacker News Reader

>If the performance is alright for my needs, why wouldn't I prefer a processor with a lower TDP?

Because 1. a processor with a lower TDP doesn't necessarily actually use less power, at least not if your cooler can dissipate much more than the TDP, which it typically can.

And 2. because you can simply limit the clock speeds of any higher TDP CPU to reach any TDP you want. If you want a 35 W 3900X or 9900K, just set the clocks to whatever you need to reach 35 W max power usage, and you're done.

Of course the lower TDP parts are typically cheaper, so it makes more sense to buy those. But that's their differentiating factor, the price, not the TDP.

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TDP is very useful if you want a quiet PC without water cooling. Under clocking may be required based on case airflow, but you want someone to be making passive CPU coolers for your socket.

Not sure what you're getting at, this is the same socket as all the other Ryzen 3000 CPUs...

Not to mention that every slightly larger air cooler is a "passive cooler". Just don't connect the fan. Or set a fan curve that disables the fan as long as the CPU temperature is sub-62 C. Or 95 C, if you really don't want them to turn on.

Yes, in this specific case it not a big deal, and they make some surprisingly effective passive coolers today. However, I have run into this issue in the past.

As to running a larger air cooler without a fan. That’s heavily dependent on case airflow. High speed case fans really defeat the purpose of a passive cooler.

You don't really need any case airflow at all, it just depends on how much performance you're willing to sacrifice. Case in point, you can run cinebench on an 8700K without any cooler at all: https://www.youtube.com/watch?v=yA0oo12rbiM

For something a bit more practical, if you're willing to get creative you can passively cool CPUs while getting fairly high performance too: https://www.youtube.com/watch?v=N-z9PidYH4E

Those are just NH-D15s, completely standard coolers with mounting brackets for pretty much every consumer socket out there.

That second video uses fans see 5:40. Lots of closely spaced thin fins actually produce less cooling without good airflow. There are real engineering reasons passive coolers have significant air gaps between the plates.

PS: In terms of sacrificing performance, let’s agree to avoid the absurd. Or as the guidelines put it: Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.

It uses fans, however IIRC the fan curves are such that they only kick in if you render videos or do something else that 100% uses the CPU, and even then they are fairly quiet. And again, if you simply limit the clock speeds and voltages, you could disable the fans completely. (Or you could just disable the fans completely in the first place and let the automatic regulation take over.)

>Lots of closely spaced thin fins actually produce less cooling without good airflow.

That is true, however Noctua coolers tend to have a fairly big gap between fins, because they are designed for very low RPM use.

>In terms of sacrificing performance, let’s agree to avoid the absurd.

Not sure why you think it's absurd - the video just shows that there is no real minimum amount of cooling required anymore, at least with Intel CPUs. Obviously you're going to have to sacrifice some performance if you go passive only.

Although I'm not even sure anymore what we're even talking about. All consumer CPUs use the same sockets. All these coolers are available for every modern consumer or "pro-sumer" platform.

> All consumer CPUs use the same sockets.

Motherboard’s use a small set of different mounting brackets for CPU coolers. But the physical CPU socket depends on several things including the physical size of the chip and thus the amount of surface area you want in contact with the the cooler.

In case you where unaware actually running a CPU at 100C will drastically lower it’s lifespan. You encounter similar issue if there are significant temperature differences across the chip. Which is why packaging includes a metal plate over the CPU even though it reduces cooling. However, this is a real tradeoff which means the contact area must be reasonably close to design spec.

Yes, bracket, not socket. What are we talking about again?

Selecting and then using passive CPU coolers. I am saying both the bracket and socket are important when choosing a cooling.

For example, when introduced there was no aftermarket passive cooling available for the AM4 socket.

Really of the 5 considerations “Does it fit the mounting bracket?” is probably the least important. Fitting the motherboard and case are mandatory. Fitting the socket and TDP have a little wiggle room. However, with mounting brackets you can generally get something to work as long as you keep firm contact and it does not wiggle around it’s fine.

Aren't you just testing the processor's internal overheating protection in that case? It might not shut down the system, but throttle itself into a snails pace.

I would suggest undervolting if you want it quieter

Most people won't undervolt, so the heatsink manufacturers won't pander to those who do. You're also limited to the manufacturer's bounds for undervolting before you're in unstable, warranty-breaking territory.

In my years long experience of looking into and building quiet PC's, going for a nice spacious case with a high-end semi passive power supply and putting in some smooth low rpm air-cooling in a nice open airflow path beats trying to go completely fan-less or god-forbid a water-cooled solution.

TDP would be useful if we standardized how it is measured, and at a whole systems level on standardized representative workloads.

Just build in a Lian-Li o11 dynamic, Corsair HX psu. I honestly don't hear it over other ambient noises around (AC, road outside, etc)... I am using an AIO 360 for top-exhaust, but it's a far cry from a custom open-loop, not much harder than a regular HSF. Been very happy with it so far.

(rambling ahead)

Using an r5-3600 as a placeholder waiting for a 3950X. Was running an i7-4790k since that dropped, and wasn't unhappy with it, but there are things where it gets sluggish with the 4 cores, etc. I have definitely noticed the performance difference. Also jumped to Linux (Pop!_OS) from 2 years of hackintosh. I need to update to kernel 5.3 and update video drivers before swapping the older rx570, with an rx5700xt aftermarket.

Actually being able to order certain parts has been a bit of a pain though.

So you're saying TDP is a measure of the efficiency of a CPU? That is if 2 CPUs are listed at the same TDP and one has a higher clock speed, then the latter would be more efficient.

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