Pentium D
Pentium D is a series of microprocessors introduced by Intel at the Spring 2005 Intel Developer Forum. A Pentium D package contains two Pentium 4 Prescott dies, unlike other multicore processors which place both cores on a single die.
The Pentium D was the first announced multicore CPU (along with its more expensive twin, the Pentium Extreme Edition) from any manufacturer intended for desktop computers. Intel underscored the significance of this introduction by predicting that by the end of 2006, over 70% of its shipping desktop CPUs would be multicore. Analysts have speculated that the clock rate race between Intel and AMD is largely over, with no more exponential gains in clock rate looking likely. Instead, as long as Moore's Law holds up, it is expected that the increasing numbers of transistors that chip-makers can incorporate into their CPUs will be used to increase CPU throughput in other ways, such as by adding cores, as the Pentium D does.
With the announcement of the Intel Core brand for their future processors, the Pentium D is the final processor to carry the Pentium brand name that has been at the forefront of Intel's products since 1993.
Smithfield
Intel released the first Pentium D products (codenamed "Smithfield") on May 26 2005, with clock speeds of 2.8, 3.0, and 3.2 GHz. The chips carried model numbers of 820, 830 and 840 respectively. An 805, clocked at 2.66 GHz with a 533 MT/s bus, appeared in early 2006.
Smithfield is made on a 90nm process with 1MiB of L2 cache per core. The Smithfield Pentium D does not support Hyper-Threading, although similar Pentium Extreme Edition counterparts do. Smithfield does not support VT, Intel's virtualization feature formerly called Vanderpool.
The Pentium D processor supports Intel's EM64T technology, the XD Bit and like most current Pentium 4s, uses the LGA775 form factor on an 800 MT/s bus. The only motherboards guaranteed to work with the Pentium D (and Extreme Edition) are those based on the 945, 955 and 975 series of chipsets, as well as the nForce 4 SLI Intel Edition. The Pentium D 820 won't work with the nForce 4 SLI Intel Edition due to some power design issues, though they were rectified for the X16 version of the chipset. Motherboards based on the 915 and 925 series of chipsets will not work at all, as the chipsets do not have support for more than one processor core (a result of Intel trying to prevent motherboard manufacturers making Xeon motherboards with the chipsets, as happened with the 875P). The 865 and 875 series chipsets do have multiprocessor support, so motherboards based on these chipsets may be Pentium D compatible, so long as the manufacturer provides an appropriate BIOS update.
As with a multiprocessor PC, the Pentium D provides significant performance improvement only with applications that have been written specifically for multiple CPUs or cores — such as most 3D rendering programs and video encoders — and in heavy multitasking situations where the PC user is running several CPU-heavy applications, and each core can handle a different application. Most business applications and games as of 2005 only use a single thread, so for these applications running alone, the Pentium D will deliver largely the same performance as an older Pentium 4 running at the same clock rate. However, applications rarely run alone on PCs running Linux, BSD-family, or Microsoft Windows operating systems.
After a week of confusion following the processor's launch, Intel officially denied a report in Computerworld Today Australia that the Pentium D includes "secret" digital rights management features in hardware that could be utilized by Microsoft Windows and other operating systems, but was not publicly disclosed. While it admitted that there were some DRM technologies in the 945 and 955 series of chipsets, it stated that the extent of the technologies was exaggerated, and that the technologies in question had been present in Intel's chipsets since the 875P.
Presler
The newest generation of Pentium D processors are based on the Presler core, a pairing of "Cedar Mill" cores. Even though Presler is a single package, that package has two dies in it, enhancing manufacturing yields of the processor over a single die approach. Presler can be supported by the same chipsets as Smithfield. It is produced using the 65 nm technology. Presler communicates with the system with an 800 MT/s FSB (while the Pentium Extreme Edition 955 and 965 use a 1066 MT/s FSB), and the two cores communicate using the FSB, just as Smithfield does. It also includes VT (Virtualization Technology, aka Vanderpool), EM64T, XD bit and EIST (Enhanced Intel SpeedStep® Technology)¹. It was released in the 1st quarter of 2006. Models include 920, 930, 940, 950 and 960 (2.8, 3.0, 3.2, 3.4 and 3.6 GHz).
¹ - First batch of Presler CPUs (revision B1) have EIST feature turned off by microcode update because of stability issues. This affects only idle power consumption and thermal dissipation. Chips with working EIST will start shipping in Q2 2006. They will have different S-Spec number which can be found in Intel errata documentation, or here
Successor
The Pentium D will be replaced by the Intel Core 2 line of processors using the "Conroe" core based upon the Intel Core Microarchitecture, scheduled for release July of 2006 [1]. Intel Core 2 processors will be released as dual core only. A single core version of the Core2 has been rumoured as a low-end release for 2007, but remains unconfirmed.
Implementation
In a single-processor scenario, the CPU-to-north bridge link is point-to-point and the only real requirement is that it is fast enough to keep the CPU fed with data from memory.
When assessing the Pentium D, it is important to note that it is essentially two CPUs in the same package and that it will face the same bus contention issues as a pair of Xeons. To use a crude analogy, one can say that instead of using a single cable between CPU and north bridge, one must use a Y-splitter. Leaving aside advanced issues such as cache coherency, each core can only use half of the 800 MT/s FSB when under heavy load.
Going from a 533 MT/s FSB to an 800 MT/s FSB, a 3 GHz Pentium 4 achieved a speed increase of up to 12%, typically around 6%. [2]