Enter Prescott What's different about Intel's latest Pentium 4 variant?
Enter Prescott
What's different about Intel's latest Pentium 4 variant?
Introduction
Intel introduced its latest Pentium 4 variation, code-named Prescott, in February 2004. As Ive discussed at length in Chapter 3 of Upgrading and Repairing PCs, the different codenames used for different versions of both Intel and AMD processors indicate significant differences in design, performance, and process technology. In this article, you will learn how Prescott differs from the existing Northwood variations and what this means for the Pentium 4s performance and future.
The First Prescotts
The first Prescott-core models of the Pentium 4 include:
- 3.40E (3.4GHz, 800MHz FSB)
- 3.20E (3.2GHz, 800MHz FSB)
- 3E (3.0GHz, 800MHz FSB)
- 2.80E (2.8GHz, 800MHz FSB)
- 2.80A (2.8GHz, 533MHz FSB)
- 2.40A (2.4GHz, 533MHz FSB)
As you can see from this list, Prescott-core processors cover a broad range of clock speeds. Although the first Prescott models are available at clock speeds already available in the Northwood core design, there are significant design differences between any given Prescott and Northwood processor at the same clock speed.
The most obvious difference between Prescott and previous Pentium 4 processors is the process technology being employed: Prescott represents the first high-volume processor to use Intels new 90 nanometer (.09 micron) process. Prescott is also the third process technology used by Pentium 4 processors. The first Pentium 4 processors used the Willamette design, which was the last gasp of Intels .18 micron process. The Socket 478 Pentium 4 Northwood processors (which replaced the Socket 423 Willamette) use a .13 micron process. Thus, Intels Pentium 4 family of processors are now based on a process which can place twice as many circuit lines in the same space as on the original Pentium 4 processors.
Reductions in process size alone are significant because the space freed up in the processor core can be used for larger cache sizes or other features, but the differences between Prescott and Northwood processors go far beyond the process size used.
New Processor Construction Technologies
A second significant difference between Prescott and Northwood is in how the processors are constructed. Prescott benefits from combining several new and recent processor construction methods for the first time:
- Copper interconnects for faster in-chip performance and less heat buildup
- Low-power transistors for lower voltage requirements and faster clock speeds
- Strained silicon (silicon whose atoms are more widely spaced than normal) to reduce resistance and improve performance
- Low-k dielectric insulation to reduce signal leakage and crosstalk
Although these improvements in Prescotts construction and design also represent significant improvements over the current Northwood core, the differences between Northwood and Prescott run even deeper.
Larger L2 Cache and Other Architectural Changes
Ever since the Pentium Pro and Pentium II processors were introduced some years ago, weve seen that processor performance is greatly influenced by the size and speed of L2 cache. Prescotts on-die L2 cache is 1MB in size. A 1MB L2 cache is twice the size of the 512KB L2 cache built into recent Northwood Pentium 4 processors and four times the size of the 256KB L2 cache found in the earliest Northwood and all Willamette Pentium 4 processors.
Even without the doubling of L2 cache size, Prescotts internal design is significantly different than Northwoods:
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Thirteen new SSE instructions (SSE3) improve the conversion of floating-point math from the integrated math co-processor to integers, reduce latency when performing complex arithmetic such as in signal processing or voice recognition, accelerate video encoding and 3D rendering.
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The processor pipeline has been extended from twenty to thirty-one steps
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To help ease slowdowns caused by the longer processor pipeline, the branch predictor, scheduler, and execution core have been redesigned
The now-standard HT Technology (hyper-threading) feature introduced on late-model Northwood processors is also available on Prescott models, and most models feature an 800MHz FSB (one model runs its FSB at just 533MHz).
The Bottom Line: Faster Performance Later, but Not Now
With the major changes in Prescotts design, how much faster is it than a Northwood-core Pentium 4 at the same clock speed? Thats almost a trick question. As analyses from various review sources show, most of the changes in Prescott (except for the new SSE3 instructions) arent intended to boost performance at current clock speeds, but rather to provide the headroom needed to increase the processors clock speed into the 4GHz and faster ranges. Except for software which uses the new SSE3 instructions, most benchmarks comparing same-speed Prescott with Northwood processors show the Northwood processor providing the same or slightly faster performance than the new Prescott design. Just as Intel did when it replaced the Pentium III with the original Pentium 4, Intel is using a processor design which trades raw performance at the low end of the clock speed scale for scalability to very fast clock speeds in the future.
At 3.6GHz or Faster, Socket 775 Required
To take full advantage of the faster clock speeds supported by Prescott, Intel is introducing a new processor form factor, Socket 775, by mid-2004. Socket 775 will be used by Prescott-core processors running at speeds above the current 3.4GHz, and will be supported by new Grantsdale and Alderwood chipsets as well as by current 865 and 875 chipsets. Consequently, to take full advantage of the clock speed improvements offered by Prescott, youll be shopping for a new motherboard.
For Further Research
Intel Websites
Intels official press release on the new Prescott-core processors is available at http://www.intel.com/pressroom/archive/releases/20040202comp.htm?iid=ipp_dlc_procp4p+info_pr2&
Learn more about the 90 nanometer process used by Prescott at http://www.intel.com/research/silicon/nanometer.htm?iid=ipp_dlc_procp4p+body_90nm&
Third-Party Websites
Anandtech benchmarks three 3.2GHz Pentium 4 processors (Northwood, Prescott, and Extreme Edition) at http://www.anandtech.com/cpu/showdoc.html?i=1965&p=1
Toms Hardware digs deep into the Prescotts design and benchmarks it to other recent Intel and AMD processors at http://www20.tomshardware.com/cpu/20040201/index.html
Motherboard maker Soltek has announced a motherboard which combines a current 865-series chipset with the new Socket 775 interface. See it at http://www.soltek.com.tw/soltek/product/products_all.php?isbn_st=SL-865Pro-775
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