HT Technology simulates two processors in a single physical core. If multiple logical processors are good, having two or more physical processors is a lot better. A multi-core processor, as the name implies, actually contains two or more processor cores in a single processor package. From outward appearances, it still looks like a single processor (and is considered as such for Windows licensing purposes), but inside there can be two, three, four, or even more processor cores. A multi-core processor provides virtually all the advantages of having multiple separate physical processors, all at a much lower cost.
Both AMD and Intel introduced the first dual-core x86-compatible desktop processors in May 2005. AMD’s initial entry was the Athlon 64 X2, whereas Intel’s first dual-core processors were the Pentium Extreme Edition 840 and the Pentium D. The Extreme Edition 840 was notable for also supporting HT Technology, allowing it to appear as a quad-core processor to the OS. These processors combined 64-bit instruction capability with dual internal cores—essentially two processors in a single package. These chips were the start of the multicore revolution, which has continued by adding more cores along with additional extensions to the instruction set. Intel introduced the first quad-core processors in November 2006, called the Core 2 Extreme QX and Core 2 Quad. AMD subsequently introduced its first quad-core desktop PC processor in November 2007, called the Phenom.
Note: There has been some confusion about Windows and multi-core or Hyper-Threaded processors. Windows XP and later Home editions support only one physical CPU, whereas Windows Professional, Business, Enterprise, and Ultimate editions support two physical CPUs. Even though the Home editions support only a single physical CPU, if that chip is a multicore processor with HT Technology, all the physical and virtual cores are supported. For example, if you have a system with a quad-core processor supporting HT Technology, Windows Home editions will see it as eight processors, and all of them will be supported. If you had a motherboard with two of these CPUs installed, Windows Home editions would see the eight physical/virtual cores in the first CPU, whereas Professional, Business, Enterprise, and Ultimate editions would see all 16 cores in both CPUs.
Multi-core processors are designed for users who run multiple programs at the same time or who use multithreaded applications, which pretty much describes all users these days. A multithreaded application can run different parts of the program, known as threads, at the same time in the same address space, sharing code and data. A multithreaded program runs faster on a multicore processor or a processor with HT Technology enabled than on a single-core or non-HT processor.
The diagram below illustrates how a single-core processor (left) and a dual-core processor (right) handle multitasking:
It’s important to realize that multicore processors don’t improve single-task performance much. If you play non-multithreaded games on your PC, it’s likely that you would see little advantage in a multi-core or hyperthreaded CPU. Fortunately, more and more software (including games) is designed to be multithreaded to take advantage of multi-core processors. The program is broken into multiple threads, all of which can be divided among the available CPU cores.