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For many developers, the brand name "Core Duo" first appeared in January 2006, as the Intel processor for Apple's next-generation Macintosh computer. Although Apple had told the world that it was moving to the x86 architecture in 2005, Core Duo name arrived with little fanfare. My own hands-on experience with the Core Duo came when I purchased an Apple iMac with an Intel Core Duo processor shortly after they came out. (But don't worry, I'm not going to start raving about my new toy in this articlethough I have to say that the 20-inch iMac kicks butt.)
To make a long story short, the Intel Core Duo processor is a new member of the Intel x86 family, and is being positioned and marketed primarily as a solution for mobile computingthat is, as part of Intel's Centrino Mobile Technology family. The Core Duo is a dual-core 32-bit processor that has all the performance goodness that you'd expect from a next-generation microprocessorfast clock and front-side bus speeds, lots of L2 cache, and more things we'll get into in a moment. But it also has other interesting features tuned for the mobile market, including dynamic power coordination, a deeper sleep mode, and advanced thermal management.
In fact, there's an entire Intel Centrino Duo Mobile Technology package that includes the Intel Core Duo processor with the Mobile Intel 945 Express chipsets and the Intel PRO/Wireless 3945 ABG Network Connectionthat is, a WiFi radio compatible with the 802.11 a/b/g specifications. Note: There are two versions of the chipset; the Intel 945GM for mainstream systems and Intel 945PM for performance-oriented systems. We're not going to get into the differences here, since they're more of interest for system builders, not developers, but the Intel 945 series chipsets do have a number of innovative features, so check out the link.
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| Figure 1. Don't you love chip pictures? I sure do! |
The Apple iMac using the Core Duo chip appears to be an anomaly in that it's not a mobile device. Indeed, the chip was chosen by Apple because its high performance, low power consumption, and cool running temperature are perfect for the low-profile, fanless iMac systems. Most of the time, though, you should expect to find the Core Duo processors in the same places that you used to find chips like Intel's Celeron M and Pentium M processors.
And yes, before you askthere is an Intel Core Solo technology, as wellbasically the same as the Core Duo, but with a single core. What we're going to talk about here, however, is the Core Duo, which appears to be the new flagship of Intel's mobile technology fleet. (See Figure 1.)
Feeds & Speeds
The Intel Core Duo is a dual-core processor that, as of the time of writing, runs with clock speeds between 1.50GHz and 2.16GHz. All versions of the processorof which there are six at presenthave a 667GHz front-side bus, and 2MB of L2 cache, which is shared between the two cores. The processor, built on 65nm wafer technology, is designed for lower power consumption. There are two 15-watt versions of the chip, running at 1.50GHz and 1.66GHz, for real power-sipping applications, and four 31-watt versions, at speeds of 1.66GHz, 1.83GHz, 2.0GHz and 2.16GHz.
(In case you're curious, the 1.83GHz chip is what's in the 17-inch iMac; my 20-inch model has the 2.0GHz processor. The newly shipping Apple MacBook Pro notebook can use either of those processors, and can also be special ordered with the 2.16GHz chip.)
How does this compare to Intel's other mobile x86 processors? Incredibly well. The single-core Intel Pentium M processor is available at speeds up to 2.26GHz, and also has a 2MB L2 cache, but only has a 533MHz front-side bus. Built on 90nm technology, the fastest version of the Pentium M processor draws 27 wattsbut is bigger and slower.
How about the Celeron M processor? The fastest version of this single-core chip runs at 1.6GHz, with 1MB L2 cache and a 400MHz system bus. Say no more, say no more...
Beyond the feeds and speeds, Intel has new architectural advances in the Core Duo processor. For example, there's a more advanced instruction branch prediction subsystem, which automatically chooses between three algorithms for best prediction performance. There is also a dedicated stack management system, which reduces the number of operations used for stack manipulation by tracking relative stack pointer changes locally.
With that settled, let's get to the parts that make the Core Duo processor good for mobility, including that dynamic power coordination, a deeper sleep mode, and more advanced thermal management than in the older single-core chips.
So Hot It's Cool
Never forget that the Core Duo is part of the Intel Centrino mobility platformand that means an emphasis on lower power consumption and low running temperatures that's as important as the drive toward performance.
Some of the power features in the Core Duo processor already existing in other Intel mobile processors. For example, the Pentium M and Celeron M share the Core Duo's power-optimized system bus (which slows down to save electricity and run cooler) and mobile voltage positioning (which dynamically lowers the chip's input voltage/frequency based on processor activity, thereby cooling the chip off).
In addition, the Core Duo processor introduces new integrated per-core digital temperature sensors and advanced thermal management. One advantage of this is that if a sensor shows that one core is running hot, the thermal system will automatically lower the frequency and voltage to both cores to cool the whole chip off.
There's also new circuitry in this dual-core chip that can resolve conflicts. You see, applications or the operating system can request, through a set of model-specific registers, that the processor run at a specific voltage/frequency in order to meet performance goals. But what if one core requests one input voltage/frequency, but the other core asks for something different? That might happen, since the cores are independentbut a dual-core processor can only run at one voltage/frequency. So, the new thermal management system will detect that situation and find a common voltage/frequencygenerally the highest oneand transition the chip to that state seamlessly.
Another new feature is Enhanced Deeper Sleep, which must be enabled in the computer's BIOS. The previous Intel mobile processors had a "deep sleep" mode, which lets the processor voltage drop to a low voltage/frequency state while maintaining context. The deep sleep mode, which Intel calls C2, is pretty deepfor example, the chip can't detect or respond to interrupts, and current draw is cut down to about 3.4 watts. (Mode C0 is normal full-speed, full-power operation. Mode C1 is enabled when one core hits a halt, and stops processing temporarily; the other core watches its bus. C1 mode runs the chip at full voltage/frequency, but it consumes less current.)
The new Enhanced Deeper Sleep mode take the power down even farther with two more modes; without getting into the details, C3 and C4 keep dropping the voltage/frequency down as far as they can go. The C4 mode even shuts down the L2 cache. C3 represents a processor current draw of 2.2 watts, and the C4 mode is a mere 1.8 watts.
What Else?
Oh, there's lot of other stuff inside the Core Duo processor that make it state of the art. For example, Intel has included Execute Disable Bit functionality, which allows the operating system to mark specific memory regions as non-executable. This can help stop malware that exploits buffer overflows or overwrite memory locations. Intel also included its VT-X technology, which supports virtualization; see "The Rings of Power: Intel's VT-x Technology and the Secrets of Virtualization."
There a lot of new technology in the Intel Core Duo processor, and that's just the chip itself; don't forget, this is part of a sophisticated mobile platform that includes the radio and advanced chipset. So, when I said that Core Duo was more than just a brandI wasn't kidding.
