Some processors come with additional extensions to their basic x86 architecture to boost their performance and/or give them more or superior value-added features. Some of these enhancements are incredibly important while others are just plain useless. So, you have to decide which of these features are important to you. Obviously, we cannot explain every special command set or feature that are released in the many processors in the market. So, I will just list down a few examples here.
Streaming SIMD Extensions (SSE)
These are extensions to SIMD instruction sets that allow a processor to manipulate multiple pieces of data with a single instruction. Most SSE versions are made by Intel and then licensed out to other chip manufacturers. SSE helps SIMD-reliant programs perform better if they have been optimized for it. The currently available versions of SSE (in order of advancement) are SSE, SSE2, Supplementary SSE3 and SSE3. The simple rule here is this - the more advanced SSE extensions your processor has, the better it will perform in multimedia operations.
This only applies to dual-core CPUs, and you'll probably have to dig around the Internet for this. P-states or known as power states dictate power consumption of the processor. When the P-state is low, which happens when the processor's load is low and there's not much work to be done, the processor consumes less power.
The problem with some dual-core processor out there is that their P-states aren't independent from core to core. This means if one core is at 100% load and the other core is idle, the P-state has to follow the active core. This means running the second, idle core at full speed, wasting power. Independent P-states allow for better power saving and thus lower electricity bills. Now, isn't that nice?
Virtualization is a technique in which a processor can handle multiple operating systems just by adding an abstraction layer which allows those operating systems to run at the same time, without affecting each other and without the use of emulation. It generally doesn't mean much to most of us, but if you're a real geek and need to run multiple operating systems at the same time, you should look for this feature.
Intel's implementation is unsurprisingly called Virtualization Technology, it was previously known as Vanderpool Technology). AMD's own solution is codenamed Pacifica. I'm just going to throw in a comment here and say that AMD's version is far superior, and has much better memory access and it doesn't come with the famous Intel memory cheat.
Simultaneous Multithreading (SMT)
This is system that allows a processor to run 2 threads at the same time. How does this work? When a thread is executed by a processor, it usually uses a functional unit of the processor. For example, if I run a floating point-based program, then the majority of its work will be done in the processor's FPU (floating point unit). This leaves the integer processing units free and unused. SMT allows for my floating point software to run on the FPU while letting another software utilize the integer units at the same time.
Generally, SMT allows a processor to improve its processing efficiency by ensuring maximum use of its processing units. However, only Intel has some form of SMT with its Hyper Threading Technology. Even then, Intel's newer Core-based processors do not support Hyper Threading although word has it that Hyper Threading will be making a comeback in the future.
No Execute Bit / Execute Disable Bit
The No Execute (NX) Bit is AMD's implementation of the Execute Disable (XD) Bit in Intel processors. These features help reduce the likelihood of getting attacked by viruses. It does so by preventing certain instructions from being executed in places like the stack, where many viruses manipulate to get their viruses payload executed. There's no need to worry too much about this feature as nearly all modern processors from the time of the late Pentium 4 and the 90nm AMD Athlon 64 processors come with this feature.
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