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The Technology Behind Dual Core CPUs
The Technology Behind Dual Core CPUs - PCSTATS
Since dual-core processors are essentially a multi-processor system in a convenient package, let's start by looking at some technologies which have contributed to AMD and Intel's newest products.
Filed under: CPU / Processors Published:  Author: 
External Mfg. Website: PCSTATS May 30 2005   M. Dowler  
Home > Reviews > CPU / Processors > PCSTATS

Highway to Hyperthreading

Hyperthreading was Intel's pre-emptive take on multi-core CPUs. The company cloned the front end of its high-end Pentium 4 CPUs, allowing the Pentium 4-HT to begin two operations at once. Once in process, the twin operation 'threads' both share the same set of execution resources, but one thread can take advantage of sections left idle by the other.

The idea of Hyperthreading is to double the amount of activity in the chip in order to reduce the problem of 'missed' memory cache requests slowing down the operation of the processor. It also theoretically ensures that less of the processor's resources will be left idle at any given time.

While Hyperthreaded CPUs appear as two logical processors to most operating systems, they are not comparable with true dual-core CPUs since each parallel pair of threads being worked on share the same execution pipeline and same set of L1 and L2 cache memory. Essentially, Hyperthreading is smoke-and-mirrors multitasking, since a single Hyperthreaded processor cannot actually perform two identical actions at the same time.

Hyperthreading does speed up certain operations which would be multi-processor capable, but never as much as a true multi-processor system, dual core or not.

One of Intel's new dual-core chips, the higher-end Pentium Extreme Edition 840 processor, also support Hyperthreading within each core, meaning that to an operating system it would appear as four logical processors on a single die. How this will work out remains to be seen.

Two Chips on One Dieā€¦ Why?

So why are both Intel and AMD suddenly peddling dual-core pushcarts so quickly down the aisle?

Several reasons; first of all; competition, competition, competition. As we will explore later in more detail, AMD built the potential for dual-core capability into its 64-bit processors right from the start. The necessary I/O structure for the second core already exists, even on single core chips. Neither company can afford to let the other get much of an edge, and AMD has already stolen way too much attention for Intel's comfort with its incredibly successful line of 64-bit processors.

It is imperative for Intel to launch a 'pre-emptive strike' and get its own dual-core technology to market quickly, lest marketshare flutter away. As for why dual core processors are being developed in the first place, read on to reason number three.

Secondly, performance. Certain 'multi-threaded' applications can already benefit greatly by allowing more than one processor to work on them at once. Dual processor systems also gain from a general decline in latency. Simply put, while there is no current way to share the current operating system load evenly between two processors, the second processor can step in and keep the system running smoothly while the first is maxed out to 100% burning a CD or encoding a file (or from a software error).

Obviously, if dual-core systems become mainstream, which it looks like they are going to, future operating systems and applications will be designed with the feature in mind, leading to better functionality down the road.

Thirdly, and less obviously, AMD and Intel are desperate. Both companies have run into barriers when it comes to increasing the raw speed of processors, or decreasing the die size. Until these roadblocks are cleared or until the general buying public understands that GHz does not directly translate to performance, both companies will be scrambling to discover any new improvements that will improve processor performance... without actually boosting core speed. This is why the idea of dual-core processors is now a reality, I'm willing to bet.

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Contents of Article: PCSTATS
 Pg 1.  The Technology Behind Dual Core CPUs
 Pg 2.  — Highway to Hyperthreading
 Pg 3.  AMD's Approach to Dual Core
 Pg 4.  Intel Approach to Dual-Core: Glue and Brown Paper
 Pg 5.  Dual Single-Core vs. Single Dual-Core?
 Pg 6.  Intel's Dual Core Lineup

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