Absolute lowest TDP Possible with 2500k

A

aphexcoil

Limp Gawd
Joined
Jan 4, 2011
Messages
322
A few questions:

1) What is the maximum undervolt achievable for a 2500k?
2) What is the maximum underclock possible for a 2500k?
3) Can individual cores be disabled in BIOS? (I.e. turn it into a dual-core chip)

I'm curious if the chip could run at .9 volts with the lowest possible underclock with two cores disabled.

How low in frequency could you take this chip in BIOS (sub 1Ghz?)
 
Educated guess tells me you could get the TDP to 20W or less. Search anandtech for a fairly recent article about TDP scaling across architectures. I believe the number is somewhere around an order of magnitude. So SB might approach 9.5W TDP with full underclock and undervolt and remain usefully efficient.

Underclock to 1000 MHz and <0.9 V might be enough for sub 20W easy.
 
I think it might be time to start experimenting :)
It's like overclocking steps in reverse.
I don't have a 2500k, so... you should let us know how far you get.
 
Do you need 2500K for that ?

Can't you set any i5 2x00 series into low multiplier ?
 
okashira said:
Educated guess tells me you could get the TDP to 20W or less. Search anandtech for a fairly recent article about TDP scaling across architectures. I believe the number is somewhere around an order of magnitude. So SB might approach 9.5W TDP with full underclock and undervolt and remain usefully efficient.

Underclock to 1000 MHz and <0.9 V might be enough for sub 20W easy.
Click to expand...

Yes, I'm actually interested in seeing if I can get the chip to run cool enough to just have a passive cooling system. I believe the lowest Core multiplier is 16 with these chips. If the voltage can be reduced to .90 - .95, and the cores reduced, I do believe you could get the chip under 20W under normal loads.
 
Michaelius said:
Do you need 2500K for that ?

Can't you set any i5 2x00 series into low multiplier ?
Click to expand...

I believe that the non K series can have the multiplier reduced, however the catch 22 here is that most people would probably have the non-K chip in a H67 motherboard which does not allow core multiplier adjustments. You would need the P67 or Z68 chipset pair with the non-K chips to reduce the multiplier. I believe this is accurate.

If anyone has a 2500k or 2600k chip (or a P67 / Z68 paired with a non-K), please let me know how low you can take it if you do attempt it.

Thanks!
 
Sounds like fun. If I have free time this morning I might take a swing at it (2500k, P67) :)

But I'm not sure what you'll gain from this. The idle power is already incredibly low, and thanks to full clock gating the extra cores consume no extra power at idle (so disabling them in the BIOS only affects your load power).
 
You can't reduce the multiplier below 16. If you do the chip still runs at 1.6.

All you have to do is change the multiplier to 1.6 and turn off Turbo. My system automatically adjusted the voltage (.9v idle, .98v all four cores loaded with Prime). This is the absolute lowest power state you can reach.

You can also play around with TDP values in the BIOS, if you want a compromise.
 
conservatively, (assuming you cant find a mobo that lets you select lower multiplier or voltage)

95W*(0.9^2/1.2^2*1600/3300) = 25.9 W
 
okashira said:
conservatively, (assuming you cant find a mobo that lets you select lower multiplier or voltage)

95W*(0.9^2/1.2^2*1600/3300) = 25.9 W
Click to expand...

But you'd almost be better off playing with the TDP values instead.

Let's say you wanted a 30w chip. You could leave the "sustained" TDP at 30w and then leave the "peak momentary" TDP at some insanely high number (I think it's 118w by default), and leave Turbo Boost on. This way the chip will turbo for a split second to 3.7 GHz (just to open apps), and then clock down to around 2 GHz sustained.

It's the same concept as Comcast's Turbo Boost internet. It feels a lot faster than it really is (because most actions on the internet take less than a second). The reason I suggest this is because the 2500k@1.6 fixed feels extremely slow.

I'll try playing around with the two TDP values today, and see if they work like this.
 
Before I can really play around with this, I need some help people:

I need some software like MSI Afterburner that will actually graph CPU speed in real-time. I'm expecting very short bursts of high speeds, and I'll likely miss it just staring at CPU-Z. Sadly, unlike GPU-Z, CPU-Z lacks real-time graphs.

They used to make exactly the utility I needed: Tmonitor. However, it's not updated for Sandy Bridge. SpeedFan can chart data, but only fan speed, temps and volts. Anyone got any other suggestions?
 
I finally found perfmon. It only samples once a second, but it's good enough.

But the performance I was expecting does not happen. Knock down the TDP to 30w and it still clocks to 3.3 GHz. So if we want snappy responsiveness with low average power, we'll probably have to play games with the turbo settings instead.
 
I can't seem to get it to use arbitrary turbo settings either. I tried setting the max non-turbo multipler to 16, and then set the turbo to crazy numbers:

regular turbo:
34, 35, 36, 37
crazy turbo:
16, 20, 25, 37

And it made no difference. The processor still idled at 1600 and ran quad core load at 3.3. I might be missing something, but it seems the turbo settings are very limited.
 
MrMike said:
Why wouldn't you just buy a 2100T?
Click to expand...

I'd like a machine that can run at low power most of the time but can crank up to top speed during a weekend when I'm doing a lot of video editing. What we really need is a chip with adjustable TDP. That would be amazing for notebooks as well.

Also, the T and S chips are, in my opinion, over-priced rip-offs. Also, don't most of the T chips have the 2000 graphics instead of the 3000 graphics? For the price of a 2100T, it just makes more sense to spend the extra $50 for a 2500k.
 
defaultluser said:
You can't reduce the multiplier below 16. If you do the chip still runs at 1.6.

All you have to do is change the multiplier to 1.6 and turn off Turbo. My system automatically adjusted the voltage (.9v idle, .98v all four cores loaded with Prime). This is the absolute lowest power state you can reach.

You can also play around with TDP values in the BIOS, if you want a compromise.
Click to expand...

Why couldn't you lower the multiple to 1.6 and lower the FSB to 50 Mhz? Wouldn't that get it below 1 ghz?

1. Set multiple to 1.6
2. Turn off all Turbo functions, EIST, etc.
3. Disable all cores except 1
4. Reduce FSB to lowest possible setting.
5. Keep lowering VID until machine cannot boot.
6. Raise VID .1 volts and try running benchmarks.
 
aphexcoil said:
I'd like a machine that can run at low power most of the time but can crank up to top speed during a weekend when I'm doing a lot of video editing. What we really need is a chip with adjustable TDP. That would be amazing for notebooks as well.

Also, the T and S chips are, in my opinion, over-priced rip-offs. Also, don't most of the T chips have the 2000 graphics instead of the 3000 graphics? For the price of a 2100T, it just makes more sense to spend the extra $50 for a 2500k.
Click to expand...


Intel already does this, during idling speedstep and turbo are enabled/disabled, respectively.
 
Check out ThrottleStop 3.00

http://www.techinferno.com/downloads/?did=1

It has very accurate data logging. Read the directions and remember to set the Minimum processor state to 100% so it doesn't have to fight against Windows. It might be able to give you the control you're looking for but Core i CPUs are very efficient so it might not give you the big savings that you are expecting.

Sandy Bridge CPUs need to operate very close to a base clock speed of 100 MHz. 50 MHz isn't going to happen.
 
aphexcoil said:
I'd like a machine that can run at low power most of the time but can crank up to top speed during a weekend when I'm doing a lot of video editing. What we really need is a chip with adjustable TDP. That would be amazing for notebooks as well.

Also, the T and S chips are, in my opinion, over-priced rip-offs. Also, don't most of the T chips have the 2000 graphics instead of the 3000 graphics? For the price of a 2100T, it just makes more sense to spend the extra $50 for a 2500k.
Click to expand...

Okay, you see Sandy Bridge chips already do this. When there is no load, the power consumption is absolute minimum. They use clock gating to disable all but one core (seriously, there is no idle power consumption difference between 2 and 4 cores in Sandy:

See Here

And Here

See a difference in idle power between 2 and 4 cores? Nope? That's how it should be. You can see clearly that this technology was already present and working in Nahelem.

In idle mode Sandy is functioning at absolute minimum. You can't really hope to improve on this. And when you load the processor, it wakes up and functions at full TDP until processing is done. This is why Intel CPUs are so sought-after for HTPCs: you get all the power of a desktop CPU whenever you want it without high idle power.

The chip will remain in idle mode so long as you don't load it. If you give it an intermittent load (like normal desktop usage), the power consumption will stay low, but you benefit because the chip will clock-up momentarily (e.g. when loading an app) to make things feel smooth. You average power remains close to minimum, yet the chip feels as snappy as if it were running at 3.3 GHz the whole time.
 
Last edited:
aphexcoil said:
Why couldn't you lower the multiple to 1.6 and lower the FSB to 50 Mhz? Wouldn't that get it below 1 ghz?

1. Set multiple to 1.6
2. Turn off all Turbo functions, EIST, etc.
3. Disable all cores except 1
4. Reduce FSB to lowest possible setting.
5. Keep lowering VID until machine cannot boot.
6. Raise VID .1 volts and try running benchmarks.
Click to expand...

What is a multiple? Are you referring to the Multiplier? Is a multiple the same thing as a multiplier?
 
Like everyone is saying idle tdp will likely not change much if at all. I've been running a 4790k at default and set all the fans to be off under 45c. When doing desktop stuff or web browsing the fan barely comes on. Even gaming at 2560x1600 I barely see it light up.
 
FnordMan said:
*snerk* Riiiight, all I see is a pointless necro for ZERO reason.
Click to expand...

I can't see the air in front of my face, but that dosen't mean that the air isn't there. My point is there is a reason, you are just blind to it.
 
Last edited:
ZodaEX said:
I can't see the air in front of my face, but that dosen't mean that the air isn't there. My point is there is a reason, you are just blind to it, which is your problem and not mine.
Click to expand...

Dude, it was clear five years ago he meant a 16x multiplier. He got those numbers from ME, and then screwed them up when he reposted them. I'm the only person in this thread who actually owns a 2500k, so you can absolutely be sure it's correct.

Can you stop acting like you're an newbie? seem to recall you've overclocked your Core i5 by +4 turbo bins, so you have at least the basics down :D

Post your GTAV Benchmark Results!


Now stop bumping dead threads for absolutely no reason. Or you'll turn into QuertyJuan.
 
Last edited:
You must log in or register to reply here.
Back
Top