The Pentium 4 is an x86 architecture microprocessor by Intel, their first all-new CPU design since the Pentium Pro of 1995. The original Pentium 4, codenamed "Willamette", ran at 1.4 and 1.5 GHz and was released in November 2000. Unlike the Pentium II, the Pentium III, and the various Celerons, it owed nothing to the Pentium Pro design, and was new from the ground up.
To the surprise of most observers, the Pentium 4 did not improve on the old P6 design in either of the normal two key performance measures: integer processing speed or floating-point performance: instead, it sacrificed orthodox performance in order to gain two things: very high clockspeeds, and SSE performance. As is traditional with Intel's flagship chips, the P4 also comes in a low-end Celeron version (often referred to as Celeron 4) and a high-end Xeon version.
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Willamette, the first Pentium 4, suffered long delays in the design process, largely because of the need for Intel to divert engineering resources to other tasks: in particular the Itanium project, but also a great many variations on the P6 core (Pentium IIs, IIIs and Celerons). Most industry experts regarded the initial 1.3, 1.4 and 1.5GHz P4 release as a stopgap product, introduced before it was truly ready because the competing AMD Athlon Thunderbird was at that time easily outperforming the elderly Pentium III, and further improvements to the Intel P-III were not yet possible.
On the test-bench, it was a major disappointment: not only was it unable to outperform the Athlon and the highest-clocked P-IIIs, it was not clearly superior even to the low-end AMD Duron. Although introduced at an astonishing US$819 (in 1000 unit wholesale quantities) it nevertheless sold at a modest but respectable rate.
In January 2001, a still slower 1.3GHz model was added to the range, but over the next twelve months, Intel gradually started pegging back AMD's lead. April 2001 brought the 1.7GHz P4, the first one to provide performance clearly superior to the old Pentium III. July saw 1.6 and 1.8GHz models, and in August 2001 Intel released 1.9 and 2.0GHz Pentium 4s.
The 2.0 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 gap was sufficiently narrow that it was a not unreasonable for partisans of either camp to claim superiority. For Intel, this was a very significant achievement. The firm had held the CPU performance crown for 16 years straight, with only two brief exceptions but (prior to the P4 2.0) had never matched the Athlons.
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 2.2GHz. Northwood combined an increase in the secondary cache size from 256k to 512k with a transiton to a new 0.13 micron process technology. By making the chip out of smaller transistors, it could run faster and yet consume less power.
With Northwood, the P4 came of age. The battle for performance leadeship 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 northern summmer of 2002, when AMD's changeover to a 0.13 micron production process was delayed and the P4s in the 2.4 to 2.8GHz range were clearly the fastest chips on the market.
A 2.4GHz P4 was released in April 2002, a 2.53GHz part in May (at which point the bus speed was increased from the original 400MHz to 533MHz), 2.6 and 2.8GHz parts in August, and a 3.06GHz Pentium 4 arrived in November. It is expected that still faster versions are possible on the current process, and that their release date will largely be determined by the availability of competing product.
The Pentium 4 performs much less work per clock tick than other CPUs (such as the Athlon or the old Pentium III), but the original design objective - sacrifice instructions per clock in order to gain raw clockspeed - has been amply fulfilled, and the P4 family of microprocessors is expected to remain a major, possibly the major player in the CPU market for some time to come.
The 3.06GHz 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.
In April 2003, Intel launched new variants, ranging from 2.4 to 3.0GHz. The key difference on these new versions was that they all supported Hyper-Threading, and ran their system buses at 800MHz. This was supposedly to compete better with AMD's Hammer line of processors. However, in the event, 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 from 333MHz to 400MHz, but it wasn't enough to hold off the new 3.0GHz P4, and was soundly beaten by the 3.2GHz variant, launched in June.
In September 2003, at the Intel Developer Forum, the Pentium 4 Extreme Edition was announced, just over a week before the launch of Athlon 64, and Athlon 64 FX. It was mostly identical to Pentium 4 (to the extent that it would run in the same motherboards), but differed by an added 2MB of Level 3 cache.
While Intel maintained that the Extreme Edition was aimed at gamers, most people viewed it as an attempt to steal the Athlon 64's launch thunder. If this was the case, then Intel's tactic failed completely, as the new chip was not only beaten by Athlon 64 and Athlon 64 FX in almost all benchmarks, but barely outperformed the Pentium 4 3.2GHz in any major tests, mostly performing as well as a 3.4GHz Pentium 4 would.
See also: List of Intel microprocessorsWillamette
Northwood
Extreme Edition
