The Core 2 DUO can operate in 64Bit making it able to address more than 4Gb of memory

x86-64
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The correct title of this article is x86-64. The initial letter is shown capitalized due to technical restrictions.

x86-64 is a 64-bit microprocessor architecture and corresponding instruction set; it is a superset of the Intel x86 architecture, which it natively supports. It was designed by Advanced Micro Devices (AMD), who have since renamed it AMD64. This architecture has also been adopted by Intel under the name Intel 64 (formerly known as EM64T, IA-32e, Clackamas Technology (CT) in reverse order).[1] The names x86-64 or x64 are sometimes used as vendor-neutral terms to collectively refer to the two nearly identical implementations.

Implementations

Intel 64 was originally implemented on the E revision (Prescott) of Pentium 4 line of microprocessors, which were supported by i915P (Grantsdale) and i925X (Alderwood) chipsets in June 2004. This was largely due to the competitive pressure of AMD's AMD64 technology implemented on Opteron and Athlon 64 lines of microprocessing units, otherwise known as the K8 core, one year earlier in 2003; the technology was largely built compatible to AMD64, and the then announced Windows XP Professional x64 Edition supporting AMD64 technology. Intel's first processor to activate the Intel 64 technology was the multi-socket processor Xeon code-named Nocona. Since the Nocona Xeon itself is directly based on Intel's desktop processor, the Pentium 4, the Pentium 4 also has Intel 64 technology built in, although as with Hyper-Threading, this feature was not initially enabled on the then-new Prescott design, likely because enabling Intel 64 did not coincide with Intel's stance on 64-bit x86 extensions at that particular time. Intel subsequently began selling Intel 64-enabled Pentium 4s using the E0 revision of the Prescott core, being sold on the market as the Pentium 4, model F. However, the revision F core was targeted at workstations. Intel's official launch of Intel 64 (under the name EM64T at that time) in mainstream desktop processors was the N0 Stepping Prescott-2M. The E0 revision also adds eXecute Disable(XD) (Intel's name for the NX bit) support to Intel 64, and has been included in the current Xeon code-named Irwindale. All 9xx/8xx/6xx/5x6/5x1/3x6/3x1 series CPUs have Intel 64 enabled, as do the Core 2 CPUs, and as will all future Intel CPUs. Intel 64 is also present in the last members of the Celeron D line.

The first Intel mobile processor supporting Intel 64 is the Merom version of the Core 2 processor, which was released on 27 July 2006. None of Intel's earlier notebook CPUs (Core Duo, Pentium M, Celeron M, Mobile Pentium 4) support Intel 64.

The following processors implement the Intel 64 architecture:

* Intel NetBurst
o Intel Xeon (some models since "Nocona")
o Intel Celeron D (some models since "Prescott")
o Intel Pentium 4 (some models since "Prescott")
o Intel Pentium D
o Intel Pentium Extreme Edition
* Intel Core microarchitecture
o Intel Xeon ("Woodcrest")
o Intel Core 2