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The skinny on quad-core processors: A buyer's guide

Posted: 25 Jul 2007 ?? ?Print Version ?Bookmark and Share

Keywords:quad-core processors? buyer's guide? Barcelona? Phenom?

Quad-core processing has become bargain country. On July 22, deep price cuts from Intel took effect, slashing the baggage for many of the chip giant's new four-way devices to less than what you used to have to fork over for a high-end dual-core part.

Your purchasing leverage is only going to increase in the coming months. That's because AMD hasn't released any quad-core parts yetIntel has more than 20and is under pressure to succeed when it finally does ship. Fortunately for buyers, that should translate into highly competitive pricing when AMD's Barcelona server quad core is released in August and the company's Phenom desktop processors follows by the end of the year.

Indeed, since the cost of dual-core chips from both Intel and AMD has come down in tandem with Intel's quad pricing moves, the only real question is: Do you want to pay a little bit more for the ultimate in performance, or would you rather snap up a real dual-core bargain?

On the practical front, the trick for individuals looking to buyas opposed to OEMs who have access to the latest chips and best deals from distributorsis that prices and availability may differ significantly from what manufacturers' announcements may have let you to believe. For example, processor street prices at the online vendors popular with individual system builders often differ from Intel's list prices. For most chips, that difference is usually to the buyer's advantage, from a measly $10 to as much as $100 or more. However, it's the reverse case for the one or two hottest processors, which are usually selling for more than Intel's posted price sheet.

What's Available?
Intel offers six quad-core desktop chips, as part of its Core 2 Quad and Core 2 Extreme families. On the server side, Intel ships some 19 quad-core Xeons, in its 5300, low-voltage 5300, and 7300 series.

Here are price comparisons for all currently available desktop and server quad-core parts.

When it comes to four-way chips, Intel is relying on its perhaps confusingly named "Core" architecture, while AMD has chosen the even less euphonious identifier "10h." Core as a microarchitectural moniker is not all that difficult to keep separate from the word's normal usage. However, there are cases where it can be a mouthful. Try saying "Intel's Core architecture Core 2 Extreme QX6850 quad-core" three times fast.

With six desktop offerings, there's no dearth of quad-core options. (Click image for larger view)

Nevertheless, Core merits attention because Intel expects to have all its processors upgraded to use the new design by the end of 2007. This includes all single- and dual-core chips, as well as well as the higher-profile quads. The defining characteristic of Core is a feature called wide-dynamic execution. This means that Core chips can carry out more instructions per clock cycle than could the earlier Netburst architecture, which powered the Pentium 4.

Core makes the move to Intel's new 45nm chip technology before the year is out. On trap for release is the "Yorkfield" desktop quad and the "Harpertown" server processor. Further afield, Intel is readying an next-generation microarchitecture code-named Nehalem. It'll also be on 45nm and is scheduled to debut in 2008.

Xeon has embraced quad in a big way, with 19 SKUs. (Click image for larger view)

The move to 45nm is important because these chips have small-sized features etched into the silicon, which enable lower-power operation. For years, the power dissipation of high-end microprocessors has been rising. Indeed, the need to keep the thermal envelop close to the 100W figure is why Intel originally went to dual-core processing. (Increasing the clock speeds of single-core chips will north of 3GHz would have pushed dissipation as high as 150W.)

Look for power dissipation to emerge as a major competitive issue, once AMD ships Barcelona and Phenom. Intel offers several low-power quad Xeon SKUs (designated "E"), which rein the thermal in to 50W. However, most of its other desktop and server parts range from 80W all the way up to 130W. Those figures aren't necessarily unacceptable, but look for Intel to try to do better when it moves to 45nm, and for AMD to come in with slightly lower power numbers out of the chute with Barcelona.

More than power, for AMD the challenge is to meet its shipping-date targets for Phenom and Barcelona. As of last week, the scrappy semiconductor vendor is pledging that it will indeed move Barcelona, probably in August, and then Phenom before the year is out.

Intel Core 2 Extreme

The devices are the flagship implementations of a new, high-performance AMD architecture known as "10h." The design incorporates numerous enhancements, including: new instructions, improved floating-point execution units, faster data transfer between floating-point and general-purpose registers, and 1Gbyte paging, to name a few. The 10h architecture also incorporates optimization to make AMD's hardware-based virtualization run faster.

Beyond the computing power packed onto the chip itself, much of the elegance of the AMD approach is evident in the way it handles I/O to external devices as well as interprocessor communications. In contrast to the traditional method of sending outbound data over a front-side bus, AMD has long used its proprietary HyperTransfer interface. In 10h, HyperTransport3 will debut, boosting the total bandwidth of the link to 20.8 Gbytes/sec.

Now it's time to get specific. Here's our desktop quad scorecard.

Core 2 Extreme QX6850
Announced in mid-July just as the price war between Intel and AMD began heating up, the QX6850 takes the crown as the hottest desktop quad you can buy. Intel is billing it as a "multitasking monster," which may be a bit of marketing hyperbole. Still, with a 3GHz clock, a 1333MHz front-side bus and 8MBYTE of shared L2 cache, it's equipped to deliver the performance goods.

As of posting time, many have written about the QX6850, but few have actually seen it. It's list-priced at $999 by Intel. However, because it's so new, it hasn't yet made its way to the usual online vendors. The only offering we could find was on eBay, where a copy had been bid up to $1,225.

Core 2 Extreme QX6800
The previous king of the quad hill, the QX6800 was listed at $1,199 prior to July 22 and is now at parity with the QX6850. That begs the question: why buy a 2.93GHz part, when you can have the full 3GHz for the same price? For now, the answer is availability. The X6800 can be readily purchased, while the 6850 still seems to be working its way through the vendor to retailer pipeline.

Interestingly, the street-pricing situation with the X6800 illustrates the truism that the top-of-the-line part at any time always commands moreusually a lot morethan list. Intel's own collection of links to authorized retailers carrying the chip shows $1,300 as the best price.

Core 2 Extreme QX6700
The QX6700 is the odd-core out in the current Intel lineup. It's got a clock speed of 2.66GHz, a 1066MHz front-side bus and 8Mbyte of L2 cache. These are exactly the same specs and the Core 2 Quad Q6700 (the difference is the absence of the "X"). Perhaps that's why the QX6700 isn't listed on Intel's July 22 price-cut list, and why it's widely assumed that the X6700 is on the way out.

However, at posting time the QX6700 remained widely available. Intel's own link to retailers shows at least a dozen offering the part. Newegg seems to have the best deal, with a $968 price that's about $30 less than Intel's early-July QX6700 list price of $999.

My own investigation turned up the lowest price available anywhere as $1,060 (not bad, right?) at TigerDirect.

Core 2 Quad Q6700
In another real-world market paradox, the Q6700 appears on Intel's July 22 price-cut list with its new, highly attractive number of $530. Unfortunately, I couldn't find any copies at most of the usual online retailing suspects. As well, while Intel lists the Q6700 on its price list and doesn't say anything about cutting the X6700's price (leading to the suspicion that it'll keep it at $999 until supplies run out), Intel's own Website links to places you can buy the X6700 but not to 6700 vendors. Go figure.

If I didn't know better, I'd say that the QX6700 and the Q6700 are the same part, and Intel's just shifted around some nomenclature. That same thinking prompted a thread, Old Extreme QX6700 vs. New Quad Q6700 on Tom's Hardware. One denizen of that forum, citing Extremetech, opined: "The Q6700 is just like the QX6700 but with a locked multiplier and a price of $530."

AMD's Phenom desktop quad is due by year's end. (Click image for larger view)

Core 2 Quad Q6600
The real bargain of the desktop quad arena is the Q6600, with a pre-July 22 price of $530 and a post-cut tag of $230. The Q6600 has a 2.4GHz clock, 8Mbyte L2 cache and 1066MHz front-side bus. As of July 22, the best real-world price appears to be $300 at

When you consider that the $300 you'll pay for the Q6000 is about what you'd pay for a dual-core 2.66GHz Core 2 Duo, it's really a no-brainer.

AMD Quad FX Platform
While AMD revs up Barcelona and Phenom for their imminent respective introductions, their desktop quad-core lineup will revolve for a little while longer around what's essentially a cobbled-together interim solution: Two dual-core Athlon 64 FX-70 series processors placed together on a dual-socket L1N64-SLI motherboard from Asus. Voila, instant quad.

AMD called this its Quad FX platform. Reviews to date have been less than enthusiastic; some have cited cooling issues.

On the plus side, the Athlon 64 FX-70 chips are all heavy duty dual-core parts. There are three: The 2.6GHz FX-70, 2.8GHz FX-72 and 3GHz FX-74. The FX-74 currently sells for $335 at NewEgg.

AMD Barcelona Server
Shortly after you read this, AMD's long-awaited Barcelona quad-core server processor should begin shipping. Early chatter has been that the initial crop of chips won't exceed clock speeds of 2GHz. This is being viewed as a disappointment, both because AMD has so much riding on its new quads and because its new "10h" architecture was expected to offer ample headroom, which AMD could exploit in its bid to outpace Intel's competing Core microarchitecture.

It's possible that AMD's clock-speed issues are related to the early challenges any company hits when manufacturing a new chip. It's also likely that Barcelona is being held back by the fact that it's on a 65nm process, rather than on newer 45nm technology. (The latter would allow clock-speed increases while keeping power dissipation within desired limits.)

Intel is currently bringing its 45nm process online at six semiconductor fabs worldwide. Penryn, its first 45nm product, should ship later this year. AMD likely won't ship any 45nm processors until late in 2008.

In advance of Barcelona, AMD has posted a flash presentation about its multicore plans. In terms of on-chip features, the four cores of Barcelona will each have separate, 512Kbyte L2 caches. They'll also share a 2Mbyte L3 cache. The processor will support a fast, DDR2/DDR3 memory interface.

Off in the (distant?) future are devices like this 80-core Intel Teraflops processor.

AMD's strengths
Barcelona will also boast wider floating-point execution units, which will double the performance of floating-point vector operations. It'll widen the instruction-fetching window to 32bytes from 16bytes. This will allow the processor to handle a complete sequence of three large instructions per cycle. Barcelona's 10h architecture adds a couple of advanced bit-manipulation instructions, and it includes many improvements to boost the performance of AMD's virtualization technology, as well as compiler-related optimizations.

Notwithstanding AMD's many strengths, the elephant in the room remains its current lack of quad-core partsa situation which will soon be remedied. However, it's worthwhile noting that, if you're either not ready to go to quad core on your desktop, or if you want a really super bargain, you might do well to consider AMD's extremely cost-effective dual-core Athlon processors. Last year, I built a dual-core PC powered by a dual-core, 2.6GHz Athlon 64 X2 5000+ processor. At the time, the part cost $745. Today, that device lists for $125. The other dual-core Athlons are also available at bargain prices. Meanwhile, AMD-powered PC runs just as fast today as it did a year ago, which is very fast indeed.

- Alexander Wolfe

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