Gecko's CPU Library

Intel Pentium 4 (Prescott) processors

Introduction: February 2004


The Pentium 4 brand refered to Intel's line of single-core mainstream desktop and laptop central processing units (CPUs) introduced on November 20, 2000 (August 8, 2008 was the date of last shipments of Pentium 4s). They had the 7th-generation architecture, called NetBurst, which was the company's first all-new design since 1995, when the Intel P6 architecture of the Pentium Pro CPUs had been introduced. NetBurst differed from the preceding Intel P6 - of Pentium III, II, etc. - by featuring a very deep instruction pipeline to achieve very high clock speeds (up to 4GHz) limited only by max. power consumption (TDP) reaching up to 115W in 3.6–3.8GHz Prescotts and Prescotts 2M (a high TDP required an additional cooling that was noisy or expensive). In 2004, the initial 32-bit x86 instruction set of the Pentium 4 microprocessors was extended by the 64-bit x86-64 set.

Pentium 4 CPUs introduced the SSE2 and SSE3 instruction sets to accelerate calculations, transactions, media processing, 3D graphics, and games. They also integrated Hyper-threading (HT), a feature to make one physical CPU work as two logical and virtual CPUs. The Intel's flagship Pentium 4 also came in a low-end version branded Celeron (often referred to as Celeron 4), and a high-end derivative, Xeon, intended for multiprocessor servers and workstations.

The Pentium 4 had an IHS (Integrated Heat Spreader) that prevented the CPU core from accidentally getting damaged when mounting and unmounting cooling solutions. Prior to the IHS, a CPU shim was sometimes used by people worried about damaging the core. Overclockers sometimes removed the IHS on Socket 478 chips to allow for more direct heat transfer. However, on LGA775 chips the IHS was directly welded to the processor core, meaning that the IHS cannot be removed without irreparably damaging the processor.

In 2005, the Pentium 4 was superseded by the Pentium D and Pentium Extreme Edition dual-core CPUs.

The Prescott core

On February 1, 2004, Intel introduced a new core codenamed "Prescott". The core used a 90 nm process for the first time, and "[it] was also a major reworking of the Pentium 4's microarchitecture—major enough that some analysts were surprised Intel didn't opt to call this processor the Pentium 5". Although a Prescott clocked at the same rate as a Northwood, benchmarks showed that a Northwood performed slightly better than a Prescott in gaming applications. However, with video editing and other multimedia software, the Prescott's extra cache and SSE3 instructions gave it a clear clock-for-clock advantage over the Northwood. The Prescott architecture allowed it to be easily set at higher clock-rates. 3.8GHz was the fastest Prescott-based processor ever mass-produced.

Upon release, many reviewers mistakenly concluded that the Prescott generated approximately 40% more heat clock-for-clock than the Northwood, and almost every review of it was negative, earning it the soubriquet PresHot. In reality, the core temperature sensor of the Prescott gave higher readings than the Northwood core temperature sensor, meaning that the increase in heat generated for CPU work done was believed to be around the 10% range. Overclockers mistakenly believed that the Northwood was a better choice for overclocking, while in reality the Prescott outperformed the Northwood and generated less heat in overclocked conditions. A shift in socket type (from Socket 478 to LGA775) was expected to reduce the heat to more acceptable levels, but in fact proved to have the opposite effect, with power requirements increasing by a further 10%. However, the LGA775 reference cooler and mounting system were somewhat better designs, so average temperatures were slightly lowered. Subsequent revisions to the processor by Intel engineers were expected to reduce average temperatures, but this never happened outside of the lowest speed grades. Prescott Pentium 4s were given the product codes 80546 (Socket 478) and 80547 (LGA775).

Finally, the thermal problems were so severe, Intel decided to abandon the Prescott architecture altogether, and attempts to roll out a 4GHz part were abandoned, as a waste of internal resources. Intel realised that it would be wiser to head towards a "wider" CPU architecture with a lower clock speed to keep heat levels down while still increasing the throughput of the CPU. Also of concern was the fact that a review showed that in games, it took a 5.2GHz Prescott core to soundly beat the performance of a 64-bit Athlon FX-55 that clocked at 2.6GHz. Considering Intel boasted at launch the Pentium 4 architecture was intended to support up to 10GHz operation with further reductions of core size, this can be seen as one of the most significant, certainly most public, engineering shortfalls in Intel’s history, as Intel engineers only planned for a stock 9GHz P4. Overclockers did not break the 8GHz barrier until the end of the Pentium 4 line on 3.0-3.6GHz CPUs, which by then had a dwindling enthusiast user base. This also meant that while Northwood ultimately achieved clockspeeds 70% higher than Willamette did, Prescott only managed a 12% rise over Northwood.

The Pentium M instead became the internal reference layout for Intel’s design teams, and P4 development was essentially abandoned. To this extent, the little-funded Israeli design team that produced the Pentium M core took over the much larger desktop development project.

Why the Prescott ended up as it did can be attributed to internal politics at Intel as much as to its specific design. The engineering group was not able to meet the marketing department's desire for ever higher clock speeds, to differentiate their products from AMD. The processor design was not able to clock at the higher speeds required for increased performance and the power consumption was simply untenable. The engineering group kept this information from people in other departments at Intel until it was too late. The termination of the P4 project, when it finally came, had consequences for many members of the management team at the desktop division, but not so much in the engineering or manufacturing groups.

Originally, two Prescott lines were released: the E-series, with an 800MT/s FSB and Hyper-Threading support, and the low-end A-series, with a 533MT/s FSB and Hyper-Threading disabled. Initially there were big problems with people who installed Windows XP Service Pack 2 on systems with these processors as an incompatibility with the BIOS, processor and SP2 coding led to systems unable to boot. Microsoft and Intel worked on a solution; users with this problem can find out how to install SP2 on a Prescott machine.

LGA775 Prescotts used a rating system, labeling them as the 5xx series (Celerons were the 3xx series, while Pentium Ms were the 7xx series). The LGA775 version of the E-series used model numbers 5x0 (520-560), and the LGA775 version of the A-series used model numbers 5x5 and 5x9 (505-519). The fastest, the 570J and 571, was clocked at 3.8GHz. Plans for 4 GHz processors were axed by Intel in favor of dual core processors, although some European retailers claimed to be selling a Pentium 4 580, clocked at 4GHz.

The 5x0J series (and its low-end equivalent, the 5x5J and 5x9J series) introduced the XD Bit (eXecute Disable) or Execute Disabled Bit to Intel's line of processors. This technology, first introduced to the x86 line by AMD and called NX (No eXecute), was able to prevent certain types of malicious code from exploiting a buffer overflow to get executed.

Intel also released a series of Prescotts supporting Intel 64, Intel's implementation of the x86-64 64-bit extensions to the x86 architecture. These were originally released as the F-series, and only sold to OEMs, but they were later renamed to the 5x1 series and sold to the general public. Two low-end Intel64-enabled Prescotts, based on the 5x5/5x9 series, were also released with model numbers 506 and 516.

5x0, 5x0J, and 5x1 series Prescotts had incorporated Hyper-Threading in order to speed up some processes that use multithreaded software, such as video editing. The 5x1 series also supported 64 bit computing.

Source: Wikipedia, the free encyclopedia.