|
Pentium 4 was a line of single-core desktop, laptop and entry level server central processing units (CPUs) introduced by Intel on November 20, 2000 and shipped through August 8, 2008.〔(【引用サイトリンク】url=http://www.tgdaily.com/content/view/33351/135/ )〕 They had a seventh-generation x86 microarchitecture, called NetBurst, which was the company's first all-new design since the introduction of the P6 microarchitecture of the Pentium Pro CPUs in 1995. NetBurst differed from P6 (Pentium III, II, etc.) by featuring a very deep instruction pipeline to achieve very high clock speeds. Intel claimed that NetBurst would allow clock speeds of up to 10 GHz in future chips; however, severe problems with heat dissipation (especially with the Prescott Pentium 4) limited CPU clock speeds to a much lower 3.8 GHz.〔http://www.pcauthority.com.au/News/163122,the-greatest-tech-u-turns-of-all-time-intel-and-netburst.aspx〕 In 2004, the initial 32-bit x86 instruction set of the ''Pentium 4'' microprocessors was extended by the 64-bit x86-64 set. The first Pentium 4 cores, codenamed ''Willamette'', were clocked from 1.3 GHz to 2 GHz. They were released on November 20, 2000, using the Socket 423 system. Notable with the introduction of the Pentium 4 was the 400 MT/s FSB. It actually operated at 100 MHz but the FSB was quad-pumped, meaning that the maximum transfer rate was four times the base clock of the bus, so it was marketed to run at 400 MHz. The AMD Athlon's double-pumped FSB was running at 100 or 133 MHz (200 or 266 MT/s) at that time. Pentium 4 CPUs introduced the SSE2 and, in the Prescott-based Pentium 4s, SSE3 instruction sets to accelerate calculations, transactions, media processing, 3D graphics, and games. Later versions featured Hyper-Threading Technology (HTT), a feature to make one physical CPU work as two logical CPUs. Intel also marketed a version of their low-end Celeron processors based on the NetBurst microarchitecture (often referred to as ''Celeron 4''), and a high-end derivative, Xeon, intended for multiprocessor servers and workstations. In 2005, the Pentium 4 was complemented by the Pentium D and Pentium Extreme Edition dual-core CPUs. ==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 (clocked at 1.13 GHz at the time), as expected. But in legacy applications with many branching or x87 floating-point instructions, the Pentium 4 would merely match or run more slowly than its predecessor. Its main handicap was a shared unidirectional bus. Furthermore, 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 (the fastest-clocked model was clocked at 1.2 GHz at the time) 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 CPU - for 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 RAM. In terms of product marketing, the Pentium 4's singular emphasis on clock frequency (above all else) 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 IPC (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 ("Prescott" most notably) 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. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pentium 4」の詳細全文を読む スポンサード リンク
|