by July 1, 2005 0 comments

A dual-core CPU physically appears as a single CPU from the outside but actually has two processors inside. It’s like having a dual-CPU system, only you don’t see two physically separate CPUs in the machine.

Dual-core CPUs for servers have been there for a long time, but it is the first time that these are coming on the desktop. The AMD Athlon 64X2 4800+ is such a dual-core processor, with two CPUs inside, each running at 2.4 GHz each and having 1 MB of L2 cache. With two processors, one can easily comprehend that it can effortlessly run two applications simultaneously. So, if you are running two applications together, they will run faster on a dual-core CPU than on a single CPU.

But when you are running only a single application, it really doesn’t make a difference whether you have two CPUs or one, until and unless you have a multi-threaded application. A thread is the smallest executable component of any application. So, if an application has the ability to execute, at least, two threads simultaneously, it will run twice as fast, minus some minor losses, on a dual-core CPU than on a conventional single core CPU. But, most applications that we use today are not multithreaded and hence cannot take advantage of a dual-core CPU. However, most PC users run more than one application at time, so they will definitely benefit by using a dual-core CPU, both in terms of performance and the experience of working while switching from one application to another. Here we compare this AMD dual core with an Intel single core P4 3.4 GHz. We first ran PCMark05, which has several tests to check system performance for things such as file compression, image processing, audio conversion, physical calculation and 3D. Here the Athlon was 41% faster than the P4, which can be attributed to the lead taken by the Athlon in the multi-threaded tests of the benchmark. In 3DMark05, a DirectX 9.0 benchmark, though the dual-core was 31% faster in the CPU tests, it was slightly slower than the P4 in the gaming tests. In DivX encoding, the P4 took 10.56 minutes to encode a complete movie, whereas the Athlon took 11.14 minutes, which is lower. So, in running single-threaded applications–DivX encoding and 3DMark games–the two cores of the Athlon give it no advantage over the higher clocked single-core P4. However, things changed, as expected, when we ran several applications-DivX encoding, MP3 encoding and virus scan-simultaneously. Here, the Athlon was much faster than the P4 in doing highly CPU intensive tasks together.

Bottom Line: From the test results, it is clear that for a typical PC usage scenario dual-core CPUs are certainly better than single-core CPUs.

Anoop Mangla

Dual core vs HyperThreading 

Intel’s Hyper Threading (HT) CPUs have only one CPU core, but appear as two CPUs to the OS and applications, by simultaneously storing two processor states. The state contains essential information about the thread being executed. By having two states, the CPU appears to execute two threads simultaneously, even though it’s only executing a single thread at a time as there is only one execution unit inside the CPU. Having two processor states reduces the time for context-switching, which takes place when the CPU switches from one thread to another making it work faster, but not as fast as a dual-core.

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