Which CPU offers best power vs heat compromise?

[Denis54]

I have decided I have been a good boy and want to offer myself a new computer. Presently, I own a P3 1.0 with 512 MB RAM. I use it mostly to surf the internet and for some light Word and Excel work. It does the job but I just want something faster.

I want a very fast and totally reliable machine that generates as little heat as possible. I am not into gaming and I do not want to overclock it. I had decided to get a P4 3.0 but have been told that they generate a lot of heat. I do not have a very large room and even with my old P3 it can get pretty hot in here.

Which CPU should I get? Should I consider an AMD? Cost is not a major issue.

 

[oldfart]

AMD 35W Mobile Athlon 64 2700+ would be "cool"

 

[Concillian]

If you want it not to get hot, the CPU is probably of secondary concern. Get an efficient POWER SUPPLY first, then worry about the CPU.

Power supply efficiencies vary between the mid to low 60% range up well into the 80% range. Considering this is working on ALL the power required for your PC, not just your CPU, signifciant improvements here, can lead to a larger overall reduction in heat load than anywhere else. Most cheapie power supplies are definitely in the LOW efficiency range. To get a supply in the 80% range you're typically paying more for the same Wattage of power supply, and most people will not do this. Efficiency just doesn't seem to sell nearly as well as price per Watt.

http://www.silentpcreview.com
has AWESOME power supply reviews that focus on noise and efficiency.

Now you probably don't need exceptional speed for what you're doing, so I'd suggest you get an AthlonXP Mobile and a decent nForce2 motherboard. Run the mobile close to stock speed with 200 FSB (they are all stock 133 FSB, but change the FSB to 200 and the multiplier to get it close to stock speed, as this will yield significantly better RAM performance) and you'll have a pretty snappy system with the processor using less than 45W (the Prescott core P4s can run closer to 80-100W). You won't be breaking any speed records, but it would be reasonably inexpensive, and definitely efficient. The A64 mobiles are a little less supported in desktop boards, while the AXP mobiles are pretty much universally supported in desktop boards.

The TDP (Thermal Design Power) of Intel and AMD processors are published on their site, but interpreting them is more difficult than it used to be, as they typically only publish the maximum power of the fastest processor, and give you little idea of what lesser processors will use (obviously less power than the fastest).

Celeron D processors are rated at 73 W TDP, Prescott P4s are going to be higher.
A64 processors are rated at 89, but the 'intermediate state at 1800 MHz / 1.4v (same as an A64 2800+) is rated at 67W
Athlon XP Mobile processors are rated at either 35W or 45W, depending on speed.

So I'd say you're looking at deciding between an AXP-Mobile, a Celeron D or an A64 2800+. I'd choose the 2800+ and a nice efficient power supply.

For reference, the 0.13 micron 1000 MHz P3 was under 30W, but the older PIII 1GHz was closer to 45W.

 

[Concillian]

Originally posted by: oldfart
AMD 35W Mobile Athlon 64 2700+ would be "cool"

Finding a desktop board that will not only accpet a mobile but will run as low as 1.2v is not very easy. Most boards support a minimum of ~1.4v if they even go that low. Plus mobile A64 support in a desktop board seems spotty based on "THE" A64 mobile thread:
http://forums.anandtech.com/me...key=y&keyword1=DTR

 

[oldfart]

Originally posted by: Concillian

Originally posted by: oldfart
AMD 35W Mobile Athlon 64 2700+ would be "cool"

Finding a desktop board that will not only accpet a mobile but will run as low as 1.2v is not very easy. Most boards support a minimum of ~1.4v if they even go that low. Plus mobile A64 support in a desktop board seems spotty based on "THE" A64 mobile thread:
http://forums.anandtech.com/me...key=y&keyword1=DTR

Seems a non A64 Mobile XP is the way to go then if you are looking for minimum heat.

 

[Markfw]

Originally posted by: oldfart

Originally posted by: Concillian

Originally posted by: oldfart
AMD 35W Mobile Athlon 64 2700+ would be "cool"

Finding a desktop board that will not only accpet a mobile but will run as low as 1.2v is not very easy. Most boards support a minimum of ~1.4v if they even go that low. Plus mobile A64 support in a desktop board seems spotty based on "THE" A64 mobile thread:
http://forums.anandtech.com/me...key=y&keyword1=DTR

Seems a non A64 Mobile XP is the way to go then if you are looking for minimum heat.

No, I would suggest a regular Athlon64 2800+ , after enabling quiet and cool, it will run WAY slower, and probably genrate less than the XP mobile !

 

[Concillian]

Originally posted by: Markfw900
No, I would suggest a regular Athlon64 2800+ , after enabling quiet and cool, it will run WAY slower, and probably genrate less than the XP mobile !

Probably true. Find out what motherboards support "Cool and Quiet" well, and this probably would be the best option. Forgot about Cool and Quiet.

 

[Denis54]

Good point about the PSU. I had not thought of that. I have an "el cheapo" power supply and wanted to replace it with a quality power supply for stability reasons. Heat will be an additional incentive to upgrade. I have visted SilentPC in the past and agree that their reviews seem excellent.

Assuming the components of a computer consume 300 watts, does that mean that a PSU with 60% efficiency will consume 500 watts (300 / 60% = 500) while a PSU with 80% efficiency will consume 375 watts (300 / 80% = 375)?

I know nothing about AMD processors. What does Cool and Quiet mean?

I know enough about computers to be able to build my own system myself but am nowhere as knowledgable as most of you are. I am looking for a straightforward CPU / motherboard combination that will be perfectly stable without requiring a lot of tweaking.

 

[Markfw]

Cool and quiet means when not needed, the cpu will automatically lower it's divider (its speed) and then won;t generate near as much heat. I don;t have the numbers, but possily as low as 20-30 watts. And when you do need the speed, it will automatically go up to rated speed. I think the 3000+ (normally 2ghz) runs at 800 mhz, and about 1/3rd of the 67 watts it would normally consume.

Anyone with better specs, please feel free to correct me, but from what I read this is close.

 

[Bar81]

You can find out the exact wattage outputs at each step in the Cool n Quiet chain in the easily accessable documentation on amd's website.

 

[iwantanewcomputer]

dothan (90nm pentium m) is the best power/heat but they are expensive out the wazoo.
a 2gh one performs about the same as equivalently clocked amd 64 but they produce something like 21 watts. which is significantly lower than the 35 watt amd 64 mobiles.

anywho i'd still get a amd 64 mobile cause the extra wattage maay seem like a big increase but compared with the total power usage of a decent laptop it isn't much.

edit... take that advise on the power supply efficiency that was commented on above. it makes a noticable difference, i upgraded from a 60% to a 75% and can definately feel less heat coming out of the power supply.

on another note, if you want to compare different speeds of processors within the same family, heat generated varies linearly with clock speed and linearly with the square of voltage. you can use this to roughly compare, say, mobile a64's to nonmobile.

finally, the specified voltage used by the processor is what the manufacturer specifies as a minimum to cover a reasonable percentage of all their processors 100% stable. some obiously end up being different than others and can use less voltage. try lowering the voltager to whatever you can get it to run stable at and it will make way less heat. i run my a64 3000 (stock 1.55V) at 1.2V and it's stable, and my processor temps are like 5-10 degrees cooler

 

[Concillian]

Originally posted by: Denis54
Assuming the components of a computer consume 300 watts, does that mean that a PSU with 60% efficiency will consume 500 watts (300 / 60% = 500) while a PSU with 80% efficiency will consume 375 watts (300 / 80% = 375)?

That is correct. And you can guess where that extra power is going...heat right into your room. This is a bonus for people who heat their home, but a detractor for people like me that live in California. My computer room is always the toughest to keep cool.

However, realize that even a heavily loaded PC will typically use less than 200-250W, so for a normal PC doing normal work your numbers should be more in the 150-200W max under typical usage with 230-300W typical wall power usage on the top end. I think even the cheapie power supplies are around 65% efficient.

Even many high end supplies are not efficient, and efficiency is often not well advertised, so you have to be VERY specific on brand, model numbers, and version numbers when shopping on power supply efficiency.

 

[AnnoyedGrunt]

Also keep in mind that PSU's are more efficient as they become more highly loaded, so if you are after a cool system, then you'll want to pick a PSU that matches your power requirements instead of picking one that is way oversized.

I like this one (this week):
http://www.newegg.com/app/View...=17-151-016&depa=1

Or the 350W or 400W version depending on your power requirements.

-D'oh!

 

[klah]

Every CG-revision desktop A64 can be run at 1.1V/1GHz using only 22W of power. C0-revision run at 1.3V/800MHz using 35W.

http://www.amd.com/us-en/asset...nd_tech_docs/30430.pdf

edit: here is a good thread about undervolting motherboards
http://forums.silentpcreview.c...ys=0&postorder=asc