Intel Pentium 4 processor families

Intel Pentium 4 is a family of high-performance microprocessors that succeeded Pentium III family. Pentium 4 CPUs are based on new NetBurst micro-architecture, which differed significantly from P6 micro-architecture used in Pentium II/Pentium III microprocessors. As an overall CPU performance is proportional to its frequency and its efficiency, to achieve better performance levels many micro-architectures, including P6, strike a delicate balance between faster CPU frequencies and improved efficiency. The NetBurst microarchitecture used different approach - it attempted to improve performance primarily by increasing CPU frequency, often at at the expense of efficiency. One of key elements in this approach was "Hyper-Pipelined Technology" - 20-stage pipeline (not counting decoder stages), that was significantly longer than in previous generation of Pentium processors. While longer pipelines are less efficient than shorter ones, they allow CPU core to reach higher frequencies, and thus increase CPU performance. To improve efficiency of very deep pipeline the Pentium 4 processors included new features: Trace Execution Cache, Enhanced Branch prediction, and Quad Data Rate bus. Intel Pentium 4 CPUs also included 144 new SIMD instructions called SSE2. Because the first generation of Pentium 4 processors, based on Willamette core, proved to be performing not significantly faster, and sometimes slower than the fastest Pentium III microprocessors, Intel added more efficiency improvements to subsequent Pentium 4 core generations - larger size of level 2 cache, faster FSB frequency, SSE3 instruction set, and Hyper-Threading technology. Other features, that were eventually added to the family, are 64-bit instruction set, and Virtualization technology.

First Pentium 4 microprocessors, based on Willamette and Northwood cores, as well as some Prescott processors, were referenced by their speed. To differentiate between Pentium 4 CPUs running at the same frequency, but having different features, Intel used one letter suffix, appended to CPU frequency:

• A - Northwood microprocessors with 512 KB L2 cache (for frequencies 2 GHz and lower), or Prescott CPUs with 1 MB L2 cache (for frequencies higher than 2 GHz).
• B - processors with 533 MHz FSB frequency.
• C - processors featuring Hyper-Threading technology and 800 MHz FSB.
• E - Prescott CPUs with 1 MB L2 cache.

Later generations of Pentium 4 CPUs, starting from Prescott core, were assigned processor numbers that uniquely identified processor frequency and features. Please see Intel desktop processor numbers page for more information.

"Pentium 4" brand was used only for high-performance single-core desktop and mobile microprocessors. Server-class CPUs, that were built on NetBurst microarchitecture, were branded Xeon and Xeon MP. Low-cost NeBurst microprocessors were manufactured under "Celeron" brand. Dual-core NetBurst-based microprocessors were branded Pentium D.

All Pentium 4s were manufactured in three types of packages - 423-pin PGA package for socket 423 motherboards, 478-pin micro-PGA package that worked in socket 478 motherboards, and pin-less 775-land LGA package that required socket 775 motherboards. Socket 478 package was used by both desktop and mobile microprocessors, while two other packages were designed for desktop systems only.