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Intel Power Consumption Then and Now
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1. From Pentium 4 to Core 2: Power Consumption Analyzed

The processor typically is the most power hungry component inside an average desktop PC. CPU power consumption first became a real issue as Intel closed in on 4 GHz with its Pentium 4, where 100+ watts was required and optimized cooling became a necessity. However, power requirements and performance did not match up with this chip. The advent of the first Pentium D 800 dual core processor made things even worse, until Core 2 Duo came to the rescue 18 months ago. We have since seen a 400% performance per watt increase, from the Pentium 4 600 series to the recent Core 2 processors. We'll look at some details of that evolution in this article.

When we looked at the typical power consumption of two AMD and Intel systems, we tracked the total power required to perform real-life tasks over time, simulated by BAPCo's SYSmark 2007. This benchmark is based on real-life applications, which process real-life workflows in a multitasking environment. While most publications release test results of minimum and maximum power requirements of components and systems, these results only tell a small part of the story. Power consumption has to be related to performance at all times, because a faster system may return to a more energy-efficient state earlier than a slow machine, and thus consume less power over time, even though the faster solution might have a higher maximum power requirement.

Our first article dealt with an AMD Athlon 64 X2 5000+ (65 nm) and Intel's Core 2 Duo E6400 Compare Prices on Core 2 Duo E6400 . Both are fast and efficient dual core processors, but Intel's Core 2 Duo won the efficiency battle due to its performance advantage, allowing it to resume an idle state quicker than the AMD processor. But how does the Core 2 Duo compare to the Core 2 Quad? And how much better is it when compared to the Pentium 4 and the Pentium D? Let's have a look!

2. Processors at 3.0 GHz

Although Intel has been adjusting the specifications for Socket 775 with every new processor generation, the socket has retained compatibility with older Socket 775 processors. While you will need a new motherboard to run a Core 2 Duo (especially the upcoming 45 nm Penryn generation scheduled for Q1 2008), it is possible to even run an old Pentium 4 in many of today's Socket 775 motherboards. Thanks to this happy circumstance, we were able to run four different processor types on our reference test system.

We picked a common clock speed, which can be set for all processors in this lineup. We would have preferred to select a clock speed in the area between 2.6 and 2.8 GHz, but it was not possible to find a common clock speed setting for all CPUs due to varying Front Side Bus (FSB) speed requirements. Hence we chose to go with 3.0 GHz, which can be reached by both Core 2 processors at FSB1333 speed and by the Pentiums at FSB800. In case of the Core 2 systems, the memory operated at 533 MHz (DDR3-1066 at CL7-7-7-20 timings), while the Pentium processors were backed by DDR3 memory running at 400 MHz (DDR3-800 and CL6-6-6-18 timings). These are the default settings as offered by the Asus P5E3 X38 motherboards. Higher memory speeds and timings would increase the power requirements, but only to a very small degree, which is certainly negligible in the context of 77 to 203 W total system power requirements.

Installing each of the following processors and setting them to run at our target clock speed of 3.0 GHz was amazingly painless. We used the Asus P5E3 Deluxe motherboard, running BIOS version 0402, dated September 19, 2007.

Pentium 4 630

The Pentium 4 600 series was an upgrade to the Pentium a 500 series, offering a 2 MB L2 cache instead of 1 MB on its 90 nm Prescott core, along with a plethora of improvements. While the P4 500 series based on the Prescott core didn't really deliver more performance than the 130 nm Northwood core - despite the doubled cache capacity - the 2 MB version introduced Enhanced SpeedStep, the upgraded Thermal Monitor 2, the Enhanced Halt State C1E and EM64T 64-bit capability.

The Pentium 4 500 series was available at up to 3.8 GHz (model 570) while the 600 series maxed out at 3.6 GHz (Pentium 4 660). Plans to cross the 4 GHz line were discussed, but heat dissipation put an end to that idea, so Intel worked towards getting the first dual core processors ready.

The Pentium 4 600 at 3.0 GHz (which means the P4-630) provided only average performance in SYSmark 2007. This is the main reason why it doesn't do well in the power consumption test, where we look at how much power the systems require to complete a full SYSmark run. Although this system's idle and maximum power requirements are second best, right after those of the Core 2 Duo E6850, the P4-630 system consumed 118 watt-hours and took one hour and 40 minutes. The Core 2 Duo E6850 took 106 watt-hours and finished the same task in one hour and ten minutes!

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We used a Pentium 4 660 and reduced the clock speed to 3.0 GHz for comparison purpose.

All Pentium-class processors on socket 775 reduce their core clock speed to 2.8 GHz when idle if SpeedStep is available and enabled.
3. Pentium D 830

The Pentium D 800 series equals two Pentium 4 600 dies on a chip, but with only 1 MB L2 cache per core. All other features of the Pentium 4 600 series were retained. Since two processing cores require more power than a single one and the power envelope of 130 W imposes a restriction, clock speeds had to be reduced a bit. As a consequence, the fastest model was the Pentium D 840 at 3.2 GHz, with the Pentium D 820 at 2.8 GHz being the entry-level dual core. Our Pentium D 800 at 3.0 GHz, which is model 830, provided slightly more performance than the Pentium 4 630, but also required the most power of all processors in our lineup: 215 watt-hours is a lot, especially when compared to the 106 watt-hours of the Core 2 Duo E6850.

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We used a Pentium D840 (3.2 GHz) and set it to 3.0 GHz (Pentium D 830).

With Enhanced SpeedStep enabled, a Pentium class FSB800 processor on Socket 775 will reduce its idle clock speed to 2.8 GHz. In case of the Pentium D 830, this is not much of a difference compared to the default clock speed of 3.0 GHz.
4. Core 2 Duo E6850

Core 2 Duo E6850 is Intel's current dual core top model. It is based on the Core microarchitecture, which was released to the desktop space in the summer of 2006. At 3.0 GHz core clock speed, utilizing two processing cores and featuring 4 MB shared L2 cache as well as a FSB1333 bus speed, it provides high performance and an adequate power requirement that stays within the 65 W power envelope. You cannot upgrade an existing Pentium D or Pentium 4 system with a Core 2 Duo processor, so you will have to purchase a new motherboard supporting the new processors, as well as DDR2 or DDR3 memory.

Core 2 processors will reduce their multiplier to 6x in idle mode with Enhanced SpeedStep enabled. In the case of a 333 MHz interface speed (FSB1333) this results in 2.0 GHz idle clock speed. Both Core 2 Duo E6850 and Core 2 Extreme QX6850 finished the complete SYSmark 2007 run within one hour and ten minutes, but the dual core processor required significantly less power - 106 watt-hours versus 131 watt-hours for the quad core, which ran at the same core clock speed.

5. Core 2 Extreme QX6850

Last but not least, we installed today's crème-de-la-crème processor into our reference system: the Core 2 Extreme QX6850. Its internal layout is pretty easy to explain, as this product basically consists of two Core 2 Duo dies, each with 4 MB L2 cache and running at FSB1333 system speed. The quad core does provide noticeably higher performance in almost all parts of the SYSmark 2007 run. However, it takes almost equally long to complete the benchmark suite, which results in a higher total power consumption due to the fact that the quad core has a higher power requirement across all tests (94 vs. 77 watt system idle power). The situation may look different for computing-intensive benchmarks, where the four cores can outperform the Core 2 Duo by a significant margin. Our testing focused on SYSmark 2007, because it draws a good picture of typical PC usage.

6. Test Setup
Plattform
CPU I Intel Core 2 Duo E6850
65 nm; 3000 MHz, 4 MB L2 Cache
CPU II Intel Core 2 Extreme QX6850
65 nm; 3000 MHz, 8 MB L2 Cache
CPU III Intel Pentium D 830
90 nm; 3000 MHz, 2 MB L2 Cache
CPU IV Intel Pentium 4 630
90 nm; 3000 MHz, 2 MB L2 Cache
Motherboard I Asus P5E3 Deluxe, Rev: 1.03
Chipset: Intel X38, BIOS 0402 (2007-09-19)
RAM Crucial BL12864BA1608.8SFB
2x 1024 MB DDR3-1066 (CL 7-7-7-20 2T)
Hard Disk Drive 1 Western Digital WD5000AAKS
500 GB, 7,200 RPM, 16 MB cache, SATA/300
DVD-ROM Samsung SH-S183
Graphics Card Gigabyte GV-RX385512H
GPU: Radeon HD 3850 (670 MHz)
RAM: 512 MB GDDR3 (830 MHz)
Sound Card Integrated
Power Supply Coolermaster RS850-EMBA
ATX 12V 2.2, 850 W
System Software & Drivers
OS Windows XP Professional 5.10.2600, Service Pack 2
DirectX Version 9.0c (4.09.0000.0904)
Platform Drivers Intel Version 8.3.1.1009
Graphics Drivers ATI Catalyst 7.11

Benchmarks and Settings

Benchmarks and Settings
Sysmark 2007 Preview Version 1.02
Official Run

7. Benchmark Results

SYSmark2007: E-Learning

SYSmark 2007: Video Creation

8. SYSmark 2007: Productivity

SYSmark 2007: 3D

SYSmark 2007: System

9. Power Consumption Tests

System Min/Max Power Consumption

Average Power Consumption for SYSmark 2007

Power Requirements during SYSmark 2007 Run

10. Performance vs. Power Consumption Diagram

SYSmark Performance per Watt

Performance Per Watt Normalized to Pentium 4 630

11. Conclusion

The advances between the Pentium 4 and the Core 2 processor generation are tremendous. Not only will Core 2 processors require 1:10 to complete an entire SYSmark 2007 run as compared to 1:35 to 1:40 for the Pentium D and Pentium 4 on our reference test system, but the Core 2 processors require less power in all system states. Normalized to a 3.0 GHz Pentium 4 630 (3.0 GHz), the Pentium D 830 offers a 4% increase in performance per watt, while Core 2 Quad at 3.0 GHz and Core 2 Duo 3.0 GHz offer a 3.6x and 4.2x better performance per watt ratio in our SYSmark 2007 test environment. These numbers were collected by tracking the entire power consumed during the benchmark run.

The total power in watt-hours required to complete a SYSmark 2007 run was cut in half by replacing the Pentium D 830 by a Core 2 Duo E6850 Compare Prices on Core 2 Duo E6850 . Since SYSmark isn't an extremely computation-intensive benchmark, you can expect even more dramatic differences when it comes to rendering, ray tracing, encryption or other forms of CPU-intensive workloads.

Intel's upcoming 45 nm Penryn has shown power requirements of only a few watts in idle, and decreased power requirements under load. This sounds promising, as it should result in an even lower power requirement to complete a given workload, as well as quicker completion time, which again helps to save power and reduce heat dissipation.