Processor Types and Specifications - Upgrading and Repairing PCs - page 78

Multicore Technology
HT Technology simulates two processors in a single physical core. If multiple simulated
processors are good, having two or more real processors is a lot better. A multicore pro-
cessor,as the name implies, actually contains two ormore processor cores in a single pro-
cessor 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 multicore processor provides virtually all the ad-
vantages 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 pro-
cessors 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
processortotheOS.Theseprocessorscombined64-bitinstructioncapabilitywithdualin-
ternal cores—essentially two processors in a single package. These chips were the start of
themulticorerevolution,whichhascontinuedbyaddingmorecoresalongwithadditional
extensionstotheinstructionset.Intelintroducedthefirstquad-coreprocessorsinNovem-
ber2006,calledtheCore2ExtremeQXandCore2Quad.AMDsubsequentlyintroduced
its first quad-core desktop PC processor in November 2007, called the Phenom.
Note
There has been some confusion about Windows and multicore or hyperthreaded 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
thoughtheHomeeditions supportonlyasingle physical CPU,ifthat chipisamulticore pro-
cessor 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
editionswillseeitaseightprocessors,andallofthemwillbesupported.Ifyouhadamother-
board with two of these CPUs installed, Windows Home editions would see the eight phys-
ical/virtual cores in the first CPU, whereas Professional, Business, Enterprise, and Ultimate
editions would see all 16 cores in both CPUs.
Multicore 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
runsfaster onamulticore processor oraprocessor with HTTechnology enabled thanona
single-core or non-HT processor.