New Intel Pentium 4 with Hyper Threading logo
The Pentium 4 is a seventh-generation x86 architecture microprocessor produced by Intel and is their first all-new CPU design, called the NetBurst architecture, since the Pentium Pro of 1995. Unlike the Pentium II, Pentium III, and various Celerons, the architecture owed little to the Pentium Pro/P6 design, and was new from the ground up. The microarchitecture of Netburst featured a very deep instruction pipeline, with the intention of scaling to very high frequencies. It also introduced the SSE2 instruction set for faster SIMD integer, and 64-bit floating-point computation.

The original Pentium 4, codenamed "Willamette", ran at 1.4 and 1.5 GHz and was released in November 2000 on the Socket 423 platform. Notable with the introduction of the Pentium 4 was the comparatively fast 400 MHz FSB. It was actually a 100 MHz quad-pumped bus, but the theoretical bandwidth was 4x that of a normal bus, so it was considered to run at 400 MHz. The AMD Athlon was running at 266 MHz (133 MHz double-pumped) at that time.



As is traditional with Intel's flagship chips, the Pentium 4 also came in a low-end Celeron version (often referred to as Celeron 4) and a high-end Xeon version intended for SMP configurations.

In benchmark evaluations, the advantages of the NetBurst architecture were not clear. With carefully optimized application code, the first P4 did outperform Intel's fastest Pentium III, as expected. But in legacy applications with many branching or x87 floating-point instructions, the P4 would merely match or even fall behind its predecessor. Furthermore, the Netburst architecture dissipated more heat than any previous Intel or AMD processor.

As a result, the Pentium 4's introduction was met with mixed reviews: Developers disliked the Pentium 4, as it posed a new set of code optimization rules. For example, in mathematical applications AMD's much lower-clocked Athlon easily outperformed the Pentium 4, which would only catch-up if software were re-compiled with SSE2-support. Computer-savvy buyers avoided Pentium 4 PCs due to their price-premium and questionable benefit. In terms of product marketing, the Pentium 4's singular emphasis on clock-frequency (above all else) made it a marketer's dream.

Old Pentium 4 (with Hyper-Threading) brand logo, replaced by one above
The two classical metrics of CPU performance are IPC (instructions per cycle) and clock-frequency. While IPC is difficult to quantify (due to dependence on the benchmark application's instruction mix), clock-frequency is a simple measurement yielding a single absolute number. Unsophisticated buyers would simply associate the highest clock-rating with the best product, and the Pentium 4 was the undisputed Megahertz champion. As AMD was unable to compete by these rules, it countered Intel's marketing advantage with the 'Megahertz myth campaign.' AMD product marketing used a "PR-rating" system, which assigned a merit value based on relative-performance to a baseline machine.

At the launch of the P4, Intel stated NetBurst was expected to scale to 10 GHz (over several fabrication process generations.) However, the NetBurst architecture ultimately hit a frequency ceiling far below expectation—the fastest retail Pentium 4 never exceeded 4 GHz. Intel had not anticipated a rapid upward scaling of transistor power leakage that began to occur as the chip reached the 90 nm process node and smaller. This new power leakage phenomena combined with the standard thermal output to create cooling and clock scaling problems as clock speeds increased. Reacting to these unexpected obstacles, Intel attempted several core redesigns ("Prescott" most notably) and explored new manufacturing technologies. Nothing solved their problems though and in 2005-6 Intel shifted development away from Netburst to focus on the cooler running Pentium M architecture. In March 2006, Intel announced the Intel Core architectures, which puts greater emphasis on energy efficiency and performance per clock. The final NetBurst-derived products will be released in 2006, with all subsequent product families switching exclusively to the Intel Core architecture.

Processor Cores

Willamette

A 'Willamette' core Pentium 4 processorWillamette, the first Pentium 4, suffered long delays in the design process. It was originally foreseen in 1998, as Intel saw the Pentium II as being their permanent line. At that time, the Willamette was only expected to breach the 1 GHz barrier upon its introduction. However, once the Pentium III was introduced, Intel obviously could not name Willamette as a Pentium II. Because its architecture was a relatively large departure from the Pentium III, it was named Pentium 4, ending Intel's Roman-numeral nomenclature system.

In November 2000, Intel released the Willamette Pentium 4 at speeds of 1.4 and 1.5 GHz. Most industry experts regarded the initial release as a stopgap product, introduced before it was truly ready. According to these experts, the Willamette was released because the competing AMD Athlon Thunderbird was at that time outperforming the elderly Pentium III, and further improvements to the P-III were not yet possible. The cores were produced using a 0.18 micrometer (180 nm) process and initially utilized Socket 423 on motherboards, with later revisions moving to Socket 478.

On the test-bench, the Willamette was somewhat disappointing to analysts in that not only was it unable to outperform the Athlon and the highest-clocked Pentium IIIs in all testing situations, it was clearly not superior to even the low-end AMD Duron. Although introduced at a price of US$819 (in 1000 unit quantities), it sold at a modest but respectable rate, handicapped somewhat by the requirement of relatively expensive Rambus Dynamic RAM (RDRAM). The Pentium III remained Intel's top selling chip, with the Athlon also selling slightly better than the Pentium 4.

In January 2001, a still slower 1.3 GHz model was added to the range, but over the next twelve months, Intel gradually started pegging back AMD's lead. April 2001 brought the 1.7 GHz P4, the first one to provide performance clearly superior to the old Pentium III. July saw 1.6 and 1.8 GHz models and in August 2001, Intel released 1.9 and 2.0 GHz Pentium 4s. In the same month, they released a new chipset that supported much cheaper PC133 SDRAM. While use of this RAM was much slower than RDRAM, the fact that PC133 was much cheaper caused the Pentium 4's sales to massively improve, displacing the Pentium III virtually overnight to become the top-selling processor on the market.

The 2.0 GHz was the first P4 to provide a serious challenge to the rival Athlon Thunderbird, which until then had been unquestionably the fastest x86 CPU on the market. Many observers concluded that the Thunderbird was still faster overall, but the performance gap was sufficiently narrow that it was not unreasonable for partisans of either camp to claim superiority. For Intel, this was a very significant achievement. The firm had held the x86 CPU performance crown for nearly 16 years straight, with only two brief exceptions prior to the release of the AMD Athlon.

Northwood

A 'Northwood' core Pentium 4 processor (P4A)In October 2001, the Athlon XP regained a clear lead for AMD, but in January 2002, Intel released Pentium 4s with their new Northwood core at 2.0 and 2.2 GHz. Northwood combined an increase in the secondary cache size from 256 KB to 512 KB (increasing the transistor count to 55 million, up from 42 million) with a transition to a new 130 nm fabrication process. By making the chip out of smaller transistors, chips can run at higher clocks or at the same speed while producing less heat. Unfortunately for many consumers, the new core also made upgrades impossible due to the requirement of a new socket (Socket 478), although later adapters were made for Socket 423 to utilize the Northwood processors.

With Northwood, the P4 came of age. The battle for performance leadership remained competitive (as AMD introduced faster versions of the Athlon XP) but most observers agreed that the fastest Northwood P4 was usually a fraction ahead of its rival. This was particularly so in the summer of 2002, when AMD's changeover to a 130 nm production process was delayed and the P4s in the 2.4 to 2.8 GHz range were clearly the fastest chips on the market.

A 2.4 GHz P4 was released in April 2002, and the bus speed increased from 400 MHz (100 MHz quad-pumped) to 533 MHz (133 MHz quad-pumped) for a 2.53 GHz part in May, 2.6 and 2.8 GHz parts in August, and a 3.06 GHz Pentium 4 arrived in November.

The 3.06 GHz processor supported Hyper-Threading (first appeared in Xeon), enabling multiple threads to be run together by duplicating some parts of the processor in order to let the operating system believe that there are two logical processors. HyperThreading was present in all Northwood CPUs, but was disabled in the core in all but the 3.06 GHz model.

In April 2003, Intel launched new 800 MHz FSB variants, ranging from 2.4 to 3.0 GHz. The key difference on these new versions was that they all supported Hyper-Threading, and ran their system buses at 800 MHz. This was supposedly to compete better with AMD's Hammer line of processors. However, only Opteron was launched, and AMD initially refused to provide an AGP controller, thus preventing the Opteron from encroaching on the Pentium 4's territory. AMD did boost the Athlon XP's bus speed from 333 MHz to 400 MHz, but it wasn't enough to hold off the new 3.0 GHz P4– and the FSB wasn't the problem; the 333 MHz to 400 MHz transition yielded little to no performance increase. A 3.2 GHz variant was launched in June and a final 3.4 GHz version was launched in early 2004.

Overclocking early stepping Northwood cores yielded a startling phenomenon. When VCore was increased past 1.7 V, the processor would slowly become more unstable over time, before dying and becoming totally unusable. This is believed to have been caused by the physical phenomenon known as Electromigration, where the internal pathways of the CPU become degraded over time due to excessive electron energy. This was also known as Sudden Northwood Death Syndrome.

Mobile Pentium 4

Pentium 4 logo, M-Variation (P4M)The Mobile Intel Pentium 4 Processor [1] was released to address the problem of putting a full Pentium 4 desktop chip into a laptop, which some manufacturers were doing. The Mobile P4 still used 70 W of power, which let it bridge the gap between the full Pentium 4 (using about 82 W), and the Mobile Pentium 4 M (using about 35 W).

Mobile Pentium 4 M

Also based on the Northwood core, the Mobile Intel Pentium 4 Processor - M [2] was released on April 23, 2002 [3] and included Intel's SpeedStep and Deeper Sleep technologies, but not Hyper-Threading. Intel's naming conventions made it difficult at the time of the processor's release to identify the processor model.There was the Pentium III mobile chip, the Mobile Pentium 4 M (or the P4-M), the Mobile Pentium 4 (or the Mobile P4), and then just the Pentium M which itself was based on the Pentium III.

Gallatin (Extreme Edition)

In September 2003, at the Intel Developer Forum, the Pentium 4 Extreme Edition (P4EE) was announced, just over a week before the launch of Athlon 64, and Athlon 64 FX (AMD64 FX). The design was mostly identical to Pentium 4 (to the extent that it would run in the same motherboards), but differed by an added 2 MB of Level 3 cache. It shared the same Gallatin core as the Xeon MP, though in a Socket 478 form factor (as opposed to Socket 603 for the Xeon MP) and with an 800 MHz bus, twice as fast as that of the Xeon MP. An LGA775 version is also available.

While Intel maintained that the Extreme Edition was aimed at gamers, some viewed it as an attempt to steal the Athlon 64's launch thunder, nicknaming it the "Emergency Edition". Curiously, many condemned Intel for cannibalizing the Xeon line, but no such complaints were aimed at AMD, who did the same with their Athlon 64 FX (which barely differed from the equivalently clocked Opterons).

The effect of the added cache was somewhat variable. In office applications, the Extreme Edition was generally a bit slower than the Northwood, owing to higher latency added by the L3 cache. Some games benefited from the added cache, particularly those based on the Quake III and Unreal engines. However, the area which improved the most was multimedia encoding, which was not only faster than the Pentium 4, but also both Athlon 64s.

A slight performance increase was achieved in late 2004 by increasing the bus speed from 800 MHz to 1066 MHz. Only one Gallatin-based chip at 3.46 GHz was released before the Extreme Edition was migrated to the Prescott core. The new 3.73 GHz Extreme Edition had the same features as a 6x0-sequence Prescott 2M, but with a 1066 MHz bus. In practice however, the 3.73 GHz Extreme Editon almost always proved to be slower than the 3.46 GHz version.

The 'Pentium 4 Extreme Edition' should not be confused with a similarly-named later model, the 'Pentium Extreme Edition', which is based on the dual-core Pentium D.

Prescott

Pentium 4 LGA775On February 1, 2004, Intel introduced a new core codenamed "Prescott." The core uses a 90 nm process for the first time, and "[it] is also a major reworking of the Pentium 4's microarchitecture - major enough that some analysts are surprised Intel didn't opt to call this processor the Pentium 5" ([4]). Although a Prescott clocked at the same rate as a Northwood, benchmarks show that a Northwood runs slightly faster than a Prescott in gaming applications. However, with video editing and other multimedia software, the Prescott's extra cache gives it a clear speed advantage over the Northwood. The Prescott's architecture allows it to be easily set at higher clock-rates. (See Overclocking.) 3.8 GHz was the fastest Prescott-based processor ever mass-produced.

Upon release, the Prescott turned out to generate approximately 40% more heat clock-for-clock than the Northwood, and almost every review of it was negative. 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.

Finally, the thermal problems were so severe, Intel decided to abandon the Prescott architecture altogether, and attempts to roll out a 4 GHz part were abandoned, as a waste of internal resources. Also of concern was the fact that reviews showed in extreme cases it took a 5.2 GHz Prescott core to match the performance of an Athlon FX-55 that clocked at 2.6 GHz [5]. Considering Intel boasted at launch the Pentium 4 architecture was designed for 10 GHz operation, this can be seen as one of the most significant, certainly most public, engineering shortfalls in Intel’s history. 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 in such a disaster can be attributed to internal politics at Intel. The marketing department wanted ever higher clock speeds, to differentiate their products from AMD. Processor design was dictated by marketing needs, rather than architectural requirements. Careers were then built on the concept of higher clock speeds, and the termination of the P4 project when it finally came, had consequences for many members of the management team at the well-funded desktop division.

Originally, two Prescott lines were released: the E-series, with an 800 MHz FSB and Hyper-Threading support, and the low-end A-series, with a 533 MHz 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; if you have this problem then find out how to install SP2 on a Prescott machine.

LGA775 Prescotts use a rating system, labeling them as the 5xx series (Celerons are the 3xx series, while Pentium Ms are the 7xx series). The LGA775 version of the E-series uses model numbers 5x0 (520-560), and the LGA775 version of the A-series uses model numbers 5x5 and 5x9 (505-519). The fastest, the 570J and 571, is clocked at 3.8 GHz. Plans for 4 GHz processors were recently axed by Intel in favor of dual core processors, although some European retailers claim to be selling a Pentium 4 580, clocked at 4 GHz. [6]

The 5x0J series (and its low-end equivalent, the 5x5J and 5x9J series) introduced the XD Bit (eXecute Disable) or Execute Disabled Bit [7] to Intel's line of processors. This technology, first introduced to the x86 line by AMD and called NX (No eXecute), can help prevent certain types of malicious code from exploiting a buffer overflow to get executed.

Intel also released a series of Prescotts supporting EM64T, Intel's implementation of the AMD64 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 EM64T-enabled Prescotts, based on the 5x5/5x9 series, were also released with model numbers 506 and 516.

5x0, 5x0J, and 5x1 series Prescotts have incorporated Hyper-Threading in order to speed up some processes that use multithreaded software, such as video editing.

Prescott 2M

Intel, by the first quarter of 2005, released a new Prescott core with 6x0 numbering, codenamed "Prescott 2M". It features new 64-bit technology (an implementation of AMD64, called EM64T by Intel), the XD Bit, EIST (Enhanced Intel SpeedStep Technology), and 2 MB of L2 cache. However, any advantage introduced by the added cache is mostly negated due to higher cache latency, and the double word size if using EM64T mode. Rather than being a targeted speed boost the double size cache is intended to provide the same space and hence performance for 64-bit mode operations.

6xx series Prescott 2Ms have incorporated Hyper-Threading in order to speed up some processes that use multithreaded software, such as video editing.

On 14 November 2005, Intel released Prescott 2M processors with VT (Virtualization Technology, codenamed "Vanderpool") enabled. Intel only released two models of this Prescott 2M category: 662 and 672, running at 3.6 and 3.8 GHz, respectively.

Cedar Mill

The final revision of the Pentium 4 was Cedar Mill, released in early 2006. This was simply a straight shrink of the 600-series core to 65 nm, with no real feature additions. Cedar Mill solved the heat problems of Prescott, with a TDP of 86 W. It has a 65 nm core and features a 31-stage pipeline (just like Prescott), 800 MHz FSB, EM64T, HyperThreading and Virtualization Technology. As with Prescott 2M, Cedar Mill also has 2 MB of L2 cache. It was released as Pentium 6x1 and 6x3 at frequencies from 2.8 GHz up to 3.8 GHz.

Successor

The original successor to the Pentium 4 was Tejas, which was scheduled for an early-mid-2005 release. However, it was cancelled a few months after the release of Prescott due to extremely high power consumption (a 2.8 GHz Tejas consumed 150 W of power, compared to around 100 W for a comparably clocked Prescott) and development on the NetBurst architecture as a whole ceased, with the exception of the dual-core Pentium D/Extreme Edition and Cedar Mill.

Since May 2004, Intel has released dual-core processors based on the Pentium 4 under the names Pentium D and Pentium Extreme Edition. They represent Intel's shift towards parallelism and their intent to eventually make the bulk of their main processor line dual-core. These came under the code names Smithfield and Presler for the 90nm and 65nm parts respectively.

The ultimate successor to Pentium 4 will be processors using the "Conroe" core based upon the Intel Core Microarchitecture, scheduled for release in mid-2006. Conroe will be a dual-core processor.

Source: http://en.wikipedia.org/wiki/Pentium_4