Dual-core processors behave like two single-core processors running on a single chip. From a performance perspective, using a dual-core processor is like using two "before mutli-core" computers fused together. Dual-core processors usually have more advantages than disadvantages when compered to single core processors and mutli-core processors usually have more advantages than disadvantages when compared to dual-core processors. The term "multi-core" includes dual-core processors, but is usually associated with processors that have three or more cores.
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Dual-core Advantages over Single-core
Dual-core processors tend to have better performance than single-core processors. Dual-core processors are able to divide information for processing by multiple units. The performance boost is most noticeable when running more than one process at once. A computer's processor has to briefly stop when it switches between difference processes, or threads, which causes a dip in performance. Dual-core processors have to switch between different threads less often than single-core processors because they can handle two at once instead of one at a time. Some processors are able to do something called "hyper-threading," which allows the processor to behave like it can handle two threads at once. However, the processor's clock speed -- the speed at which it can process tasks -- does not increase with hyper threading.
Dual-core Disadvantages over Single-core
Single-core CPUs usually lose in performance comparisons against dual-core CPUs. However, a single-core CPU can outperform a dual-core CPU when the CPU has a significantly greater clock speed, which is measured in gigahertz, or GHz. A 3.8 GHz single-core processor will outperform a 1.8 GHZ dual-core processor when processing a single task. Additionally, some programs are not designed to run on more than one core, so a 3.8 GHz single-core processor will run that particular program faster than a 3.2 GHz dual-core processor. Running a program that is only able to use one core at a time on a dual-core processor is like only being able to use four cylinders on an eight-cylinder engine car: You get half the performance. Single-core processors can also get better battery life on a mobile device than a dual-core processor because the single-core processor uses less electricity to operate. However, more recently made dual-core processors tend to be more energy efficient than older single-core processors.
Dual-core Advantages over Multi-core
Dual-core processor advantages over multi-core processors mirror the single-core processor advantages over dual-core processors. Dual-core processors can get better battery life on mobile devices than similar-speed multi-core processors, and dual-core processors with higher clock speeds than multi-core processors are faster at running tasks that are not optimized for more than one core.
Dual-core Disadvantages over Multi-core
Dual-core processors are not able to handle as many tasks at the same time as efficiently as multi-core processors. Multi-core processors have the same advantages over dual-core processors that dual-core processors have over single core processors. A CPU with four cores has the ability to handle four threads, or eight with hyper-threading, at the same time, which can greatly reduce the need to change threads compared to a dual-core processor.