Intel Pentium Extreme Edition (Smithfield XE) processors
Introduction: May 2005
The Pentium D brand refered to two series of dual-core 64-bit x86 processors with the NetBurst microarchitecture. Each CPU comprised two single-core dies (CPUs) - next to each other - in one multi-chip module package. The brand's first processor, codenamed Smithfield, was released by Intel on May 25, 2005. Nine months later, Intel introduced its successor, codenamed Presler, but without offering significant upgrades in design, still resulting in a relatively high power consumption. By 2005, the NetBurst processors reached the clock speed barrier at 4GHz due to a thermal (and power) limit exemplified by the Presler's 130W TDP (a high TDP required additional cooling that can be noisy or expensive). The future belonged to more efficient and slower clocked dual-core CPUs on a single die instead of two. The dual die Presler's last shipment date on August 8, 2008 marked the end of the Pentium D brand and also the NetBurst microarchitecture.
The dual-core CPU ran very well with multi-threaded applications (typical for transcoding audio and video, compressing, photo and video editing and rendering, ray-tracing). The single-threaded applications alone, including most games, did not benefit from the second core of dual-core CPU over equally clocked single-core CPU. Nevertheless, the dual-core CPU was useful to run both the client and server processes of a game without noticeable lag in either thread, as each instance could be running on a different core. Furthermore, multi-threaded games benefited from the dual-core CPUs.
The Smithfield XE core
Pentium Extreme Edition was introduced at the Spring 2005 Intel Developers Forum, not to be confused with the "Pentium 4 Extreme Edition" (an earlier, single-core processor occupying the same niche). The processor was based on the dual-core Pentium D branded Smithfield, but with Hyper-threading enabled, thus any operating system saw 4 logical processors (2 physical x 2 virtual cores). It also had an unlocked multiplier to allow overclocking. It was initially released as Intel Pentium Extreme Edition 840 at 3.20GHz, in early 2005, at a price point of $999.99 (OEM version) or $1,200 (retail). The only chipsets that worked with the Extreme Edition 840 were the Intel's 955X, NVIDIA's nForce4 SLI Intel Edition, and ATi Radeon Xpress 200. Using a Pentium Extreme Edition branded CPU with an Intel 945-series chipset will disable Hyper-threading effectively turning the processor into a Pentium D branded equivalent.
Source: Wikipedia, the free encyclopedia.