Pentium 4
Pentium 4 is a series of single-core CPUs for desktops, laptops and entry-level servers manufactured by Intel. The processors were shipped from November 20, 2000 until August 8, 2008. All Pentium 4 CPUs are based on the NetBurst microarchitecture, the successor to the P6.
The Pentium 4 [|Willamette] introduced SSE2, while the [|Prescott] introduced SSE3 and later 64-bit technology. Later versions introduced Hyper-Threading Technology. The first Pentium 4-branded processor to implement 64-bit was the Prescott , but this feature was not enabled. Intel subsequently began selling 64-bit Pentium 4s using the "E0" revision of the Prescotts, being sold on the OEM market as the Pentium 4, model F. The E0 revision also adds eXecute Disable to Intel 64. Intel's official launch of Intel 64 in mainstream desktop processors was the N0 stepping Prescott-2M.
Intel also marketed a version of their low-end Celeron processors based on the NetBurst microarchitecture, and a high-end derivative, Xeon, intended for multi-socket servers and workstations. In 2005, the Pentium 4 was complemented by the more advanced dual-core-brands Pentium D and Pentium Extreme Edition, all were succeeded at the top range by the Core 2 brand, while production continued until 2008, with Pentium 4 replaced by Pentium Dual-Core or called Pentium from 2009.
Intel officially declared end-of-life and discontinued Pentium 4 processors on July 13, 2010 when support for Windows 2000 and Windows XP SP2 ended.
Microarchitecture
In benchmark evaluations, the advantages of the NetBurst microarchitecture were unclear. With carefully optimized application code, the first Pentium 4s outperformed Intel's fastest Pentium III, as expected. But in legacy applications with many branching or x87 floating-point instructions, the Pentium 4 would merely match or run slower than its predecessor. Its main downfall was a shared unidirectional bus. The NetBurst microarchitecture consumed more power and emitted more heat than any previous Intel or AMD microarchitectures.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 lower-clocked Athlon easily outperformed the Pentium 4, which would only catch up if software was re-compiled with SSE2 support. Tom Yager of Infoworld magazine called it "the fastest CPUfor programs that fit entirely in cache". Computer-savvy buyers avoided Pentium 4 PCs due to their price premium, questionable benefit, and initial restriction to Rambus' RDRAM. In terms of product marketing, the Pentium 4's singular emphasis on clock frequency made it a marketer's dream. The result of this was that the NetBurst microarchitecture was often referred to as a marchitecture by various computing websites and publications during the life of the Pentium 4. It was also called "NetBust", a term popular with reviewers who reflected negatively upon the processor's performance.
The two classical metrics of CPU performance are instructions per cycle and clock speed. While IPC is difficult to quantify due to dependence on the benchmark application's instruction mix, clock speed is a simple measurement yielding a single absolute number. Unsophisticated buyers would simply consider the processor with the highest clock speed to be the best product, and the Pentium 4 had the fastest clock speed. Because AMD's processors had slower clock speeds, 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 Pentium 4, Intel stated that NetBurst-based processors were expected to scale to 10 GHz after several fabrication process generations. However, the clock speed of processors using the NetBurst microarchitecture reached a maximum of 3.8 GHz. Intel had not anticipated a rapid upward scaling of transistor power leakage that began to occur as the die reached the 90 nm lithography and smaller. This new power leakage phenomenon, along with the standard thermal output, created cooling and clock scaling problems as clock speeds increased. Reacting to these unexpected obstacles, Intel attempted several core redesigns and explored new manufacturing technologies, such as using multiple cores, increasing FSB speeds, increasing the cache size, and using a longer instruction pipeline along with higher clock speeds.
The code cache was replaced by a trace cache which contained decoded microoperations rather than instructions with advantage of eliminating instruction decoding bottleneck so that the design can use RISC technology. This came with a disadvantage of less compact cache taking up more chip space and consuming power.
These solutions failed, and from 2003 to 2005, Intel shifted development away from NetBurst to focus on the cooler-running Pentium M microarchitecture. On January 5, 2006, Intel launched the Core processors, which put greater emphasis on energy efficiency and performance per clock cycle. The final NetBurst-derived products were released in 2007, with all subsequent product families switching exclusively to the Core microarchitecture.
Testing and validation
According to Bob Bentley, presenting on behalf of Intel at the 38th annual Design Automation Conference, "The microarchitecture of the Pentium 4 processor is significantly more complex than any previous IA-32 microprocessor, so the challenge of validating the logical correctness of the design in a timely fashion was indeed a daunting one." He hired a team of 60 recent graduates to help with testing and validation.Processor cores
Pentium 4 processors have an integrated heat spreader that prevents the die from accidentally being damaged when mounting and unmounting cooling solutions. Prior to the IHS, a CPU shim was some times used by people worried about damaging the core. Overclockers sometimes removed the IHS from Socket 423 and Socket 478 chips to allow for more direct heat transfer. On Socket 478 Prescott processors and processors using the Socket LGA 775 interface, the IHS is directly soldered to the die or dies, making it difficult to remove.Willamette
Willamette, the project codename for the first NetBurst microarchitecture implementation, experienced long delays in the completion of its design process. The project was started in 1998, when Intel saw the Pentium II as their permanent line. At that time, the Willamette core was expected to operate at frequencies up to about 1 GHz. However, the Pentium III was released while Willamette was still being finished. Due to the radical differences between the P6 and NetBurst microarchitectures, Intel could not market Willamette as a Pentium III, so it was marketed as the Pentium 4.On November 20, 2000, Intel released the Willamette-based Pentium 4 clocked at 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 Pentium 4 was released because the competing Thunderbird-based AMD Athlon was outperforming the aging Pentium III, and further improvements to the Pentium III were not yet possible. This Pentium 4 was produced using a 180 nm process and initially used Socket 423, with later revisions moving to Socket 478. These variants were identified by the Intel product codes 80528 and 80531 respectively.
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, but it was not superior to the budget segment's AMD Duron. Although introduced at prices of $644 and $819 for 1000 quantities to OEM PC manufacturers, it sold at a modest but respectable rate, handicapped somewhat by the requirement for relatively fast yet expensive Rambus Dynamic RAM. The Pentium III remained Intel's top selling processor line, with the Athlon also selling slightly better than the Pentium 4. While Intel bundled two RDRAM modules with each boxed Pentium 4, it did not facilitate Pentium 4 sales and was not considered a true solution by many.
In January 2001, a still slower 1.3 GHz model was added to the range, but over the next twelve months, Intel gradually started reducing AMD's leadership in performance. In April 2001 a 1.7 GHz Pentium 4 was launched, the first model 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 GHz Pentium 4s. In the same month, they released the 845 chipset that supported much cheaper PC133 SDRAM instead of RDRAM. The fact that SDRAM was so much cheaper caused the Pentium 4's sales to grow considerably. The new chipset allowed the Pentium 4 to quickly replace the Pentium III, becoming the top-selling mainstream processor on the market.
The Willamette code name is derived from the Willamette Valley region of Oregon, where a large number of Intel's manufacturing facilities are located.
Northwood
In January 2002, Intel released Pentium 4s with a new core codenamed Northwood at speeds of 1.6 GHz, 1.8 GHz, 2 GHz and 2.2 GHz. Northwood combined an increase in the L2 cache size from 256 KB to 512 KB with a transition to a new 130 nm fabrication process. Making the processor out of smaller transistors means that it can run at higher clock speeds and produce less heat. In the same month boards utilizing the 845 chipset were released with enabled support for DDR SDRAM which provided double the bandwidth of PC133 SDRAM, and alleviated the associated high costs of using Rambus RDRAM for maximal performance with Pentium 4.A 2.4 GHz Pentium 4 was released on April 2, 2002, and the bus speed increased from 400 MT/s to 533 MT/s for the 2.26 GHz, 2.4 GHz, and 2.53 GHz models in May, 2.66 GHz and 2.8 GHz models in August, and 3.06 GHz model in November. With Northwood, the Pentium 4 came of age. The battle for performance leadership remained competitive but most observers agreed that the fastest-clocked Northwood-based Pentium 4 was usually ahead of its rival. This was particularly so in mid-2002, when AMD's changeover to its 130 nm production process did not help the initial "Thoroughbred A" revision Athlon XP CPUs to clock high enough to overcome the advantages of Northwood in the 2.4 to 2.8 GHz range.
The 3.06 GHz Pentium 4 enabled Hyper-Threading Technology that was first supported in Foster-based Xeons. This began the convention of virtual processors under x86 by enabling multiple threads to be run at the same time on the same physical processor. By shuffling two program instructions to simultaneously execute through a single physical processor core, the goal is to best utilize processor resources that would have otherwise been unused from the traditional approach of having these single instructions wait for each other to execute singularly through the core. This initial 3.06 GHz 533FSB Pentium 4 Hyper-Threading enabled processor was known as Pentium 4 HT and was introduced to mass market by Gateway in November 2002.
On April 14, 2003, Intel officially launched the new Pentium 4 HT processor. This processor used an 800 MT/s FSB, was clocked at 3 GHz, and had Hyper-Threading technology. This was meant to help the Pentium 4 better compete with AMD's Opteron line of processors. Meanwhile, with the launch of the Athlon XP 3200+ in AMD's desktop line, AMD increased the Athlon XP's FSB speed from 333 MT/s to 400 MT/s, but it was not enough to hold off the new 3 GHz Pentium 4 HT.
The Pentium 4 HT's increase to a 200 MHz quad-pumped bus greatly helped to satisfy the bandwidth requirements the NetBurst architecture desired for reaching optimal performance. While the Athlon XP architecture was less dependent on bandwidth, the bandwidth numbers reached by Intel were well out of range for the Athlon's EV6 bus. Hypothetically, EV6 could have achieved the same bandwidth numbers, but only at speeds unreachable at the time. Intel's higher bandwidth proved useful in benchmarks for streaming operations, and Intel marketing wisely capitalized on this as a tangible improvement over AMD's desktop processors. Northwood 2.4 GHz, 2.6 GHz and 2.8 GHz variants were released on May 21, 2003. A 3.2 GHz variant was launched on June 23, 2003 and the final 3.4 GHz version arrived on February 2, 2004.
Overclocking early stepping Northwood cores yielded a startling phenomenon. While core voltage approaching 1.7 V and above would often allow substantial additional gains in overclocking headroom, the processor would slowly become more unstable over time with a degradation in maximum stable clock speed before dying and becoming totally unusable. This became known as Sudden Northwood Death Syndrome, which was caused by electromigration. This phenomenon would later occur on Raptor Lake CPUs.