Prescott clock speeds will initially range from 2.8GHz to 3.4GHz. To keep Prescott-based P4s distinct from older "Northwood" cores, Intel is tacking an "E" on to the product names, so they'll be called the Pentium 4 2.8E or 3.2E. The product mix gets most confusing at 2.8GHz, where one could buy four different Pentium 4s: the 2.8GHz (a Northwood core with a 533MHz front-side bus), the 2.8C (Northwood again, but with an 800MHz bus), the 2.8A (Prescott with a 533MHz bus), or the 2.8E (Prescott with 800MHz bus). Clear as mud?
Anatomy of a die shrink
One of the most notable changes is the use of a strained silicon substrate. When stretched slightly, the lattice structure of silicon atoms spreads out and opens up, allowing for freer flow of electrons. This lower resistance, in turn, allows for smaller gate lengths and faster transistors. Intel claims here that its new process only adds two percent to manufacturing costs, which is remarkable given the use of strained silicon.
Intel's 90nm process replaces the fluorine-doped silicon oxide dielectric film used previously with an even lower capacitance carbon-doped oxide film. This process also employs a layer of nickel silicide, essentially as caps on the transistors, to lower resistance versus the cobalt silicide used in Intel's 130nm process. The result of these changes is gate lengths as small as 50nm. SRAM cells are down from 2 square microns to 1.15.
Not only is the 90nm process smaller, but Intel is also manufacturing Prescott using seven layers of copper interconnects, instead of the six used at 130nm. All told, the changes shrink the Pentium 4's die size to 122 mm2, from 145 mm2 for Northwoodthis despite the fact Prescott's transistor count is 125 million, over twice Northwood's 55 million transistors.
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