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Is Intel's Prescott P4 too hot to handle?

Evidence mounts of mounting evidence
Thu Jul 01 2004, 11:58
SINCE INTEL introduced its latest Pentium 4 processor, instances of Prescott thermal concerns have been popping up all over the Web.

We should all know by now that Prescott, Intel's 90 nanometre desktop processor, did not deliver the clock-for-clock performance gains that Northwood did over Willamette. However, because of its much longer pipeline, Intel's newest core should scale much higher in frequency than its predecessor.

Turning up the heat
One side effect of Intel's 90 nm process is a marked increase in thermal levels. X-bit labs noted this when it compared Prescott to its fellow 3.2 GHz brethren.

Processor state - Idle/Burn (deg C)
P4 Prescott - 45/61
P4 Northwood - 30/48
P4 Gallatin - 32/51

The reviewer wasn't too charitable when he said: "I don't think I need to comment on these numbers. Prescott processors warm up much more during active work than their predecessors. Note that we measured the CPU performance during the tests carried out in an open testbed. I am scared to imagine what happens to Prescott when we close the system case…" (1).

Well, Sudhian Media did just that, but it went one stage further. It tested Prescott in a small form factor case (Shuttle SFF), which is probably the toughest thermal environment that the chip will experience. Its article headline tells you what's coming: "Intel's Prescott Meets SFF - What's That Burning Smell?" The fifth graphic tells the whole story. (2).

When the 3.2 GHz Prescott was overclocked to 3.57 GHz, the temperature of the Shuttle power supply hit 94 degrees Celsius, which killed it. It looks like Shuttle will have to beef up its power supply design to make it fully Prescott compliant.

GamePC made the following Prescott observation after it carried out its non-overclocking thermal tests using a Shuttle SFF PC: "We would not be surprised to see future Prescott CPU's hitting the 160-170°F range in Shuttle boxes. Amazingly, the CPU didn't have any problems running so hot, but obviously, it's hard to feel comfortable with a system running this hot internally. If given the choice, Northwood is a much better CPU for SFF environments, at least until Prescott's thermal issues are solved." (3).

The power supply failure above is one example where Prescott exposed a weak link. Another area of concern will be the voltage regulator components on the motherboard. During Prescott testing, HardOCP had a supporting motherboard block melt because of the elevated temperature it was under. It observed: "The IC7-MAX3 did do something that we have never seen before. If you have noticed, we have used square blocks of plastic foam to elevate our boards for years now while we are testing them. The IC7-MAX3 got so hot that it actually melted the plastic block into a liquid form." (4).

Related to HardOCP's findings, motherboard maker MSI has limited the BIOS voltage options on one of its "Prescott approved" motherboards, which will be disturbing to enthusiasts that overclock. MSI says - last but one paragraph: "The 865PE Neo2-P Platinum Edition is designed to support the Intel® next generation Pentium 4® processor: Prescott. However, owing to the different manufacturing process and power management, we've made some voltage limits in the BIOS to protect the Prescott P4 CPU from burning out. Meanwhile, you'll also find that there is no CPU voltage settings to adjust. This is also for system protection." (5).

You don't have to suffer Prescott's thermal baggage
ZDNet corroborated these thermal concerns as well. It measured the total system power used (Watts) in two different scenarios - a standard PC using standard components, and a high-end PC using a top-line graphics card. Worse case numbers shown. (6).

Standard PC - No load/Full load/Cool'n'Quiet
P4 3.2 GHz Prescott - 114/192
P4 3.2 GHz Northwood - 76.5/144
Athlon 64 3200+ - 106/115/70.6

High-end PC - No load/Full load/Cool'n'Quiet
P4 3.2 GHz Prescott - 165/248
P4 3.2 GHz Northwood - 113/182
Athlon 64 3200+ - 158/168/120

For the standard PC on full load, the Prescott system used 33% more power than its Northwood stablemate, and 67% more energy than its Athlon 64 adversary. For the high-end PC on full load, Prescott again used more power than the aforementioned systems, which was 36 and 48 percent more respectively. When activated, you can see how AMD's CoolnQuiet technology lowered the power used.

What should be clear to the enthusiast is that Prescott will add significantly to the power load of the power supply and the motherboard. AMD use to be accused of being the manufacturer of furnace processors, but that clearly is not the case anymore. Intel now rightly wears that crown with Prescott.

Athlon 64 motherboards that support AMD's Cool 'n' Quiet technology have the ability to dynamically lower the processor's frequency and voltage when the workload doesn't require it. Because it produces less heat in this low power state, the processor's fan speed is automatically reduced as well, which lowers the decibel level on the ears.

Enthusiasts concerned about Prescott's power use do have alternative options - Northwood Pentium 4 while it's still available, Athlon 64/Mobile Athlon 64, and Athlon XP/XP-M for entry-level enthusiasts.

Curbing the fiery furnace
The chip giant obviously has plans to improve Prescott's thermal performance so that frequency gains can be realised. But as Intel achieves those goals, it seems probable that higher frequency devices will continue to push the thermal envelope. Intel's latest 3.6 GHz Prescott P4 (LGA 775) is a case in point; it raises the thermal design power (TDP) from 103 W for the 3.4 GHz Prescott (socket 478) to 115 W for the 3.6 GHz device.

Processor thermal concerns were highlighted during Intel's spring IDF. During his presentation, CTO Pat Gelsinger showed a well used slide - a rising straight line over time against temperature - that demonstrated the ever increasing thermal requirements of each succeeding processor generation. He said about that challenge: "We need a fresh approach," Gelsinger said. "We need an architectural paradigm shift." Maybe Gelsinger should have listened more intently to the chip giant's former chief architect.

Ignore the chief architect at your peril
During a recent talk, former Intel chief architect Bob Colwell showed a slide that was titled: "Moore's Law is not free any more". It showed an exponential curve over time against transistors, clock rate, power, bugs, and design errata. The point he was making was that exponential trends are not sustainable - he said that trees don't grow to the sky, you're going to hit a wall and break. It seems evident today that for power, Intel has already hit that wall, and as a consequence, frequency headroom for production parts is now a problem.

Colwell's talk also highlighted concerns he had about the Pentium 4. He wanted to take that chip in a different direction but management wanted faster clocks. Intel chose faster clocks.

If there is a lesson that Intel may learn from the Colwell experience, it is that a strategic plan that goes against the advice of the chief architect may prove very costly indeed.

Prescott primer before you buy
It's pretty clear that Intel's Prescott is a power guzzler. Running Prescott in a SFF case seems to be the most challenging thermal scenario. Overclocking in that environment would appear to be problematic. Those who decide to go with Prescott as an upgrade will have to make sure that their power supply, case, and motherboard are all up to the job. Also, remember that "Prescott approved" has caveats - a la MSI, so remember to read the fine print.

A possible side effect that Prescott could have on motherboards and power supplies is accelerated life, as these systems are thermally stressed to a much higher temperature than before. Do your homework before you buy. µ

See Also
Fully fledged Intel Prescott could soak 150 watts
Shuttle claims it's licked Prescott problems
Mobile Athlon XP-M 2500+ overclocks like crazy
Will the 35W Athlon 64 be the next OC king?
Former Intel chief architect shoots from the hip



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