Monday, October 26, 2009

Update on new system

Even with the stock HSF, AMD's Phenom II X3 720 is a nice overclocker.

Case - Cooler Master Storm Sniper
Power Supply - Corsair Professional series 850 watts

Motherboard - Asus M4A785TD-V EVO
BIOS 4.10

Processor - Phenom II X3 720 BE, stock HSF
Bus, 200 * 17 = 3.4 Ghz, auto voltage
NB, 200 * 12 = 2.4 Ghz, auto voltage

Memory - OCZ AMD Gold Edition, 4 DIMMs, Unganged
Total, 4 * 2 GB = 8 GB's
Clock, 667 Mhz, 1.45 volts
Timing, 7-7-7-19-30-2T

Memory tested with a two full cycles of MemTest86 4.0 from boot CD. Processor tested with Prime95 using one thread per core of In-Place, Large FFT (maximum heating) which hits just over 50 C. Also tested with two passes of Intel Burn Test, 10 cycles each. IBT is only useful to raise the temperature; you have to ignore the numeric results since IBT has errors in calculation.

I had one bad DIMM from OCZ that I RMA'd without too much trouble and got my replacement. The Case had a bad circuit board which prevented the pretty blue fan lights from coming on. They sent me a new top which I swapped out with the old one and the lights work fine now. I haven't had any other problems with hardware. With Windows Vista though there were a couple of things. When it first installed some of the menu items like Accessories were missing. Later it developed a Component Store error which could not be fixed. This prevented upgrading to service pack 2. In the end I had to reformat and reinstall Vista. This install seems to be working just fine and it successfully installed service pack 2. I will upgrade to Windows 7 as soon as Microsoft sends me my copy. Theoretically it was shipped today.

I am curious though about Intel Nehalem based systems. I've seen people who claimed with a straight face that 85 C was okay because the CPU wouldn't be damaged until the temperature hit 100C. I'm baffled where this notion comes from. It seems to be a naiive assumption that since thermal throttling occurs at 95 C that anything below that must be safe. Thermal throttling seems analogous to me to a rev limiter on an engine. Engines have a green band where the engine normally runs, a yellow band where damage will eventually occur and a red band where damage can occur at any time. Rev limiters are normally set to hold RPMs within the yellow band and prevent moving up into the red. However, I have seen limiters which even allowed moving slightly into the red. If you aren't familiar with the notion of green, yellow, and red bands for RPM range this is an excerpt from an engine manual:

Idle 1300-1600 RPM
Continuous cruise 3200-4800 RPM Peak torque @ 3600/100% throttle
Max continuous 5000 RPM Peak in-flight HP/100% throttle
Max peak / Time 5600 RPM / 5 Minutes Ignition rev limiter set @ 5900
Never exceed 6000 RPM Engine mechanical limit.

Here we have a direct comparison to processor temperatures. Obviously Idle would be the no load temperature with minimum clock. Continuous would be up to Intel's maximum temperature which on i7 920 would be 70 C. This is the green band where the processor was designed to run. Next we have the yellow band which for this engine runs from 4800 - 5900 RPM where the rev limiter kicks in. This is directly analogous to the temperature band on i7 920 which runs from 70 - 95 C where thermal throttling occurs. The never exceed limit is 6000 RPM which again is directly comparable to Intel's 100 C limit.

Now, notice that the maximum peak is 5600 RPM even though the rev limiter doesn't kick in until 5900 RPM. Peak is not an RPM that you can run on a continuous basis; the maximum continuous is only 5000 RPM. Increased wear occurs if you run above 5000 RPM for any length of time. The same thing happens when running a CPU above rated temperatute. The big difference though is that the engine can be overhauled whereas the procesor will have to be scrapped. I've seen overclockers blandly assume that Intel temperatures were fine because "thermal throttling didn't occur". This is almost certainly incorrect. Occasional jumps into the band above 70 C shouldn't cause any noticeable effects just as they don't when briefly revving into the yellow band with a engine. However, continuously running above 70 C is not just asking for trouble; it is sending out an engraved invitation.

So, what exactly does this mean in real terms? First of all, both Intel and AMD expect CPU's to have a lifespan of 30,000 - 50,000 hours. Secondly, for every 10 C you go over 70 C you decrease life expectancy by half. So if you ran something like Prime95 continuously with it stressing your processor to 85 C, life expectancy would be 1.2 - 2.0 years. The problem is that it would be difficult to reach this temperature with something like Folding@Home and few other applications would run continuously. Routine tasks like web browing and word processing will hardly stress the CPU above idle temperatures. In other words, if your temps stayed under 70 C then the couple of hours a day you spent playing Call of Duty with your temps hitting 85 C would be neglible on CPU life.

If you ran your CPU at 75 C continuously doing something like encoding and then hit 90 C for three hours a day playing Crysis then your CPU life would be 2.1 - 3.5 years. If you planned to upgrade in three years it might be worth the risk. However, keep in mind that your video card and memory (and sometimes the power supply) get their cooling air from inside the case. If the case temps are high because of heat from the CPU then it would be a good idea to either upgrade the case fans or to avoid overclocking memory or GPU. And since the power supply typically has twice the life expectancy of the CPU I would avoid using a case where the PS has to draw from the interior. For example, in my case, the PS draws cooling air through a screen on the bottom so it doesn't get warm air from inside the case. Over at Toms Hardware you can see a perfect example of a poorly design system where they tried to stuff a hot i7 920 into a micro-ATX case with two GTX 295 graphic cards while using a PS that draw from inside the case:

The problem was that the cooler’s heatpipes would interfere with the DFI LANParty Jr. motherboard’s heat sinks, making it impossible to mount the CPU cooler in such a way that would force CPU-heated air towards the rear case fan, and therefore, out of the case.

We were left with no choice except to channel heated air upwards (toward the PSU) or downwards (toward the video cards). Given these choices, we would prefer to force it upwards toward the PSU so that it could be channeled through the power supply and out of the rear of the case.

Unfortunately, in this specific application, the PC Power and Cooling S75QB PSU does not pull air from below like a lot of ATX PSUs do–one fan pulls air in from the front of the PSU, and then another fan forces it out the rear. The bottom of the PSU is solid, and pushing CPU heated air upwards into a brick wall isn’t our idea of a good time.

We were left with no choice at all, really: we had to push the CPU-heated air downward, towards the graphics cards.

Contrary to what the fools at THG suggest, the last thing you want a good power supply to be doing while under heavy load is acting as an exhaust fan for the CPU. This irrational power-supply-as-cooling-fan notion began with Intel's desperate BTX case. Likewise, if your CPU runs hot then avoid using the the cheap video cards that exhaust inside the case. In another THG build they put four cheap, internally exhausting video cards inside the case. However, the NZXT Tempest case they used includes two front fans, one rear fan, and two top fans so it would be able to handle the case cooling with no problem. However, once again we see the completely bogus link with the power supply:

It's a little ironic that the reason a PC Power & Cooling PSU wasn't ideal for our previous microATX build is precisely what makes it so attractive this time around. In our last SBM, we experienced less-than-ideal airflow out of our CPU cooler because the power supply didn't pull air from below.

This is absurd. The cooling air will be drawn in the front and exhausted out the three fans in the top rear corner. Having the power supply sucking in air on the bottom of the case would actually reduce the cooling efficiency since you want it to exhaust out the top. The builder even recognizes this point in opposition to his previous statement about the power suppply:

The Xigmatek Dark Knight can dissipate a good amount of heat for the $37 price tag, which we’ll use to push the hot CPU and GPU heated air upwards and towards the NZXT Tempest case's upward-facing exhaust fans.

I'm not against overclocking. I specifically bought a BE processor to make overclocking easier and the system more stable. The highest clock I can reach and still boot Windows is 3.6225 Ghz (17.5 x 207 Mhz). I can boot, run SuperPi, open a paint program, paste, clip and save the image. I can open a browser, go to a website, and upload the resulting image. I can do this at 3.6225 Ghz and with the stock HSF. I don't consider this practical though. The highest clock I can hit and still pass Prime95 is 3.485 Ghz. Again, on the stock HSF. So, I run mine at 3.4 Ghz to have some margin of stability. Temperature has never been a problem. The max temperature for my processor is 73 C. With Prime95 I can hit about 51 C and with Intel Burn Test I can hit 55 C. Both are well below the maximum.

I guess reasons like these are what turned me off from the idea of running a Nehalem system. You never hear Intel enthusiasts talk about the stock HSF; they always use a premium cooler like a Zalman or Thermaltake. In fact, when Intel sent out socket 1156 i5's and i7's for review they included Thermalright MUX 120 coolers. This heatsink is 160mm's tall which means it would fit in my case as long as I don't have a fan on the side panel but would not fit in most cases. When the manufacturer has to include a premium cooler something is definitely amiss.

The bottom line is that the days of the cool running Penryn's are gone. However, we also know that Penryns ran cool because the memory controller was in a separate chip. Now that Intel has the memory controller on the CPU die the entire thermal bill must be paid from one socket instead of going Dutch with the Northbridge. I would guess that Intel enthusiasts want to pretend that they can get the benefits of the IMC while keeping the low thermals of Penryn. Since this doesn't work so well, they resort to downplaying the notion of going over the rated temperature, and they seem to avoid doing stress testing with programs like Prime95. That all seems very strange to me. You pretend you have a robust processor and then handle it with kid gloves. I think the denial started when reviewers found out that Turbo often wouldn't work in a standard case with a video card. Also strange is the notion of touting Turbo as a great feature but then having to turn it off to overclock. I like AMD's Cool and Quiet and it stays on and running all the time. This allows the processor to clock down to 800 Mhz at idle.

Now, I have encountered the same attitude about ignoring common sense limits on AMD hardware but you have to search a lot harder to find it. For example when I was installing the processor on the motherboard the stock HSF seemed pretty hefty to me. I had a hard time imagining using something much heavier. However, I was wrong; the actual AMD spec for socket AM2/AM3 indicates a weight limit of 500 grams which is quite a bit heavier than the stock unit. 500 grams should be plenty but these example heatsinks are compatible with AM2/AM3 and heavier:

Sunbeam CR-CCTF - 590 grams
XIGMATEK HDT-D1284 - 667 grams
ASUS Royal Knight - 790 grams
Xigmatek THOR'S HAMMER HDT-S126384 - 800 grams
ZALMAN CNPS10X Extreme - 920 grams

All sorts of nasty things can happen if you flex the motherboard too much. Just as we find Intel enthusiasts who rationalize running over temperature limits I'm sure the AMD enthusiasts who buy these heatsinks would have similar rationalizations for going over the socket weight limit. However, I'm not looking for denial, excuses, or rationalization. A decent processor should be capable of running in a standard case with the stock HSF and still passing Prime95. If you have to make excuses why your system can't do this then you don't have much of a system.

While I'm at it I might as well talk about the AMD 785 integrated graphics. Dawn of War is almost more than the graphics can handle; I have to run it on absolute minimum settings. Sins of a Solar Empire actually has the same graphic requirement so again turning things off is a good idea. DemiGod has higher graphic requirements and is jittery at 1280 x 1024 even with minimum settings so you'll be near the bottom in graphic resolution. All of these games are enhanced for multi-core but apparently not enough to offset slower graphics. In other words, I'm not sure that my X3 processor is noticeably faster than it would be with an X2 and I'm pretty sure that an X4 wouldn't make much difference. They are playable but more resolution would be nice. Presumably these would be unplayable with Intel X58 graphics or older ATI 690G. Of course, low end discreet cards are not that expensive unless you are trying for a budget system. I had been looking at AMD 4890 cards before the 5000 series was released. Now it looks like the 5770 Juniper cards have displaced the 4890's and have Direct X11 support as well. I had considered 5850 but the cost is higher than I want to go. I'll have to revisit the performance when I upgrade.