Pentium® D

The Pentium D was Intel's first mainstream dual core processor (launching three weeks after the Extreme Edition) and came into existence with the transition from focusing on increasing single threaded performance and instruction level parallelism to looking towards bringing increased thread level parallelism and multi-threading performance to the desktop. This involved the same basic principle as had been used for years in servers and workstations utilising multiple Xeon processors but rather than featuring multiple sockets brought two processing cores into a single package.

The first generation, 800-series, Pentium D was launched on May 26th, 2005, and featured the Smithfield core. This was essentially a pair of Prescott core's placed side-by-side within a single die. Each core had 1MiB of L2 cache however as with Xeon's cache coheriency had to be carried out across the front side bus.
From the outset EM64T, XD Bit and EIST were all supported giving the processor a well rounded feature set. Hyper-threading however was disabled and only available on the Pentium Extreme Edition version of the chip.
As it was based on the Prescott core the Smithfield shared its performance and thermal problems. As there were two cores it never made it past 3.2GHz vs. the 3.8GHz of its single core equivalent as at this speed it had a TDP of 130w.
If a program could make use of both CPU cores then the Pentium D would outpace the Pentium 4, if it couldn't then a higher clock speed Pentium 4 would be a better choice. The Pentium D became popular for media encoding but in other areas it struggled.
In December the Pentium D 805 was released as a low cost dual core processor. This ran at 2.66GHz on a 533MHz front side bus as opposed to 800MHz for the 2.8 - 3.2GHz parts. It became reasonably popular with overclockers as the cheapest dual core processor available and with good headroom given sufficient cooling.

January 16th, 2006, saw the launch of the 900-series, Presler core, chips. These were built using the new 65nm process and weren't so much based on the Cedar Mill as were literally a pair of them next to each other.

While Smithfield featured a pair of cores next to each other on a single piece of silicon, Presler was two entirely seperate cores. This had several manufacturing advantages as it meant if a single core was bad (entirely faulty or simply not capable of a certain speed) then with Smithfield both cores would have to be downgraded to a lower speed bin or thrown away completely. With Presler only one core was lost or could be paired up with another lower bin one.
Presler featured the other upgrades that Cedar Mill received over Prescott in the form of 2MiB of L2 cache per core and support for Virtualization Technology.
Early chips however did not have EIST support as this was disabled due to stability issues, it was re-enabled for the C-1 stepping.
Since it was based on the 65nm process thermals were vastly improved over the Smithfield, especially with the EIST enabled C-1's, and the Pentium D 960 was launched at 3.6GHz.
Non-Virtualization enabled parts were launched around the same time, these had a part number 5 lower than the equivilent VT enabled parts (e.g. 2.8GHz Pentium D 920 became the 915).

Pentium® D 950

Owned from new, currently in use in a home system.