We’ve been spoiled. As computer buyers, we’ve assumed it to be a law of nature that processor speeds would double every year. The phenomenon is widely referred to as “Moore’s Law.” And even though Gordon Moore’s 1965 processor prediction has been updated to doubling every 18 months, Intel and competitor AMD remain locked in a mega- and giga-hertz arms race.
Facing increasing physical obstacles approaching 4 gigahertz processors and beyond, the two chip makers were looking another way, aside from sheer speed, to preserve the CPU market from stagnation. Intel first brought us hyper-threading, and now, dual-core processors. Both Intel and AMD are prepared to spread the dual-core dogma, complete with full-bore marketing hoopla tugging at your purse strings.
If Intel and AMD have their way, in a few years we will all be assimilated. Dual-core for everyone. But what about now? Should you jump to the head of processor pack?
Hyperthreading? Dual-Core? Huh?
Dual-core processors actually arrive on the heels of Intel’s hyper-threading, or HT, technology, its first foray into improving processor efficiency. Hyper-threading and dual-core share some common principles, with some different results.
In late 2002, Intel introduced hyper-threading technology to its Pentium 4 line as it broke the 3-gigahertz (GHz ) barrier. Normally, a single CPU operates in a mode known as “single-threaded.” It’s like having one hand. That hand can handle only one task at a time. HT technology effectively gave the CPU a second hand. With the capability to execute two threads at once, more work can be accomplished at the same time.
Technically, hyper-threading creates two logical processors inside one physical core. But since both hands share the same body, they have to share those 3GHZ, too. The HT compromise is that when both hands are working, each has to work more slowly than it would alone.
Hyper-threading helped Intel battle back against gains made by AMD, since its Athlon processors consistently outperformed Intel CPU’s in single-threaded applications at a given speed. Many, but not all, Pentium 4 processors now feature HT, but both Intel and AMD knew that hyper-threading was a stepping stone to dual-core processors.
High-performance computers have long relied on multiple-processor configurations. Servers with dual or even quad Xeon or Opteron processors offer major, but expensive, horsepower. Motherboards with additional sockets and circuitry to support multiple processors, and distribute instructions between them, are limited. Dual-core technology replaces some of these expensive logistics to bring multiple processors to the masses.
A dual-core processor stacks two independent execution cores into one physical housing. They then share the broader infrastructure for managing communications between the processor and the motherboard. Unlike hyper-threaded processing, each execution unit in a dual-core CPU is fully independent and can operate at its maximum speed, running two threads simultaneously. In principle, each core can also support hyper-threading, although only premium models do. In that case, one physical dual-core processor could run up to four threads simultaneously, albeit with the limitations inherent to HT.
At this time, Intel’s Pentium Extreme Edition (with HT support), Pentium D series and AMD’s Athlon 64 X2 series feature dual-core processors.
The Dual-Core Advantage
Like hyper-threading, dual-core processors operate in parallel rather than in combination. For example, the entry-level Pentium D 820 dual-core processor runs at 2.8 GHz per core. This is not the equivalent of one 5.6 GHz CPU. Each processor can execute only one chore at a time (the 820 does not support HT), at a maximum speed of 2.8 GHz.
The dual-core advantage is efficiency. Imagine you need to send a car to complete two errands. Dual cars driving 50 miles per hour will complete the errands more quickly than one car driving 75 miles per hour. Of course, the dual-car advantage shrinks if the faster car drives 200 miles per hour. So, a dual-core Pentium D 820 is not a 5.6 GHz processor — which doesn’t exist — but it can offer a notable advantage over a single 2.8 GHz CPU.
Just how much of an advantage depends on how you use your computer. Having two processor cores is helpful only if you put both of them to work.
Because Windows 2000, XP and XP SP2 support multiple processors (known as SMP, or symmetric multi-processing), a dual-core CPU will multitask efficiently. You can apply a filter in Photoshop and browse the Web, without a noticeable slowdown in either. Like Windows, current versions of Linux also support multiple processors.
Some applications themselves are multithreaded, such as Windows Media Encoder 9. When compressing video to WMV format, Windows Media Encoder will divide the workload into multiple threads, sharing them between processors. As a result, the whole job gets done faster.
One single-threaded application running alone will experience no speed boost at all from a dual-core CPU, since it will use only one processor. Because most applications today are single-threaded, the great benefit from dual-core comes from a multi-tasking scenario where you often run several large applications at the same time.
As dual-core processors catch on, it is expected that more applications will support multithreaded processing. This seems great at first glance, since they will effectively run faster dividing their workload across both processors. But consider a multitasked, multithreaded environment — in this case, several applications running at the same time will be spreading their workloads between cores, effectively competing with each other. This is actually the same inefficient scenario we have right now on a typical single-threaded CPU.
Ultimately, the dual-core benefit varies with your usage profile. Most people will gain some performance from a dual-core processor, but how much and at what cost?
The bottom line right now is that dual-core provides the maximum cost-benefit ratio to people who multitask several single-threaded applications or dedicate processing time to a demanding multithreaded application.
At press time, an HP Pavilion PC with the entry-level Pentium D 820 dual-core processor and the standard trimmings runs about $1,000. The equivalent system with AMD’s dual-core Athlon 64 X2 4200 weighs in at about $1300. A third equivalent system built around the single-core Athlon 64 3500 also hits the $1,000 mark. But note — you can build a budget-friendly Athlon 64 3500 system, with less-costly multimedia features, for about $500. For now, the dual-core processors are being packaged in premium systems.
Put head-to-head in single-threaded business applications, such as the Microsoft Office suite, the single-core Athlon 64 3500 slightly outperforms the dual-core Pentium D 820. In this scenario, with light multitasking, a $500 single-core system could equal or exceed the performance of the $1000 dual-core system, with other factors — memory, disk space, etc. — being equal.
Encoding HD video in Windows Media Encoder 9 is multithreaded. In this case, the Pentium D 820 churns through the job nearly 50 percent faster than the Athlon 64 3500 — but at twice the price, in the case of the HP Pavilions.
Of course, PC prices change rapidly, and the dual-core price-performance tradeoff will probably have already shrunk by the time this story hits the Web.
Traditionally, certain software platforms — operating systems and databases in particular — are licensed on a per CPU basis. Therefore, if you install Microsoft Windows 2003 Server on a dual-CPU machine, you may require two licenses to be in the legal right. Dual-core processors have thrown some legal analysts for a twist — are they one CPU, or two?
Microsoft, for its part, has chosen to be pro-active and eliminate any confusion. Rather than define its licenses per-processor, they now license per-socket. This means that traditional dual-CPU machines with two physical processors continue to require two licenses, but a dual-core machine with only one physical processor socket needs only one license.
Other companies, like Oracle and IBM, have not entirely given up counting dual-core processors as more than one CPU. Although in some cases, they count them as less than two. That confusion alone should be the only yellow flag you need — if you’re thinking of going dual-core, check with your software vendors. Additional license fees could drive up the dual-core cost beyond its performance advantage. Of course, open-source software is insulated from this legal tussle.
Now or Later
Intel’s roadmap for 2006 and beyond strongly suggests that multi-core processors — dual and more — are the way of the future. AMD will be sure to echo this sentiment in the marketplace.
For buyers, the situation means that today’s premium priced dual-core CPU will be tomorrow’s commodity. By the same token, today’s 3+ GHz, single-core CPU’s are heading for retirement, and therefore good deals.
Of course, this is the eternal life cycle of CPU pricing. Always has been. Chances are you’ll own a dual-core PC sooner or later. The decision is whether you want to pay for it now, or then.
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