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Although chips including Intel's Pentium 4 series could be overclocked beyond 4GHz before the arrival of AMD's Bulldozer series, it was an AMD's FX chip that marked the debut of the first factory-clocked processor above 4 GHz years later.
The first CPU to reach a clock speed of 4 GHz was the Pentium 4 570 released in November 2004 as part of Intel's NetBurst microarchitecture, but this milestone wasn't achieved out of the box. The Pentium 4 570 had a base clock speed of 3.8 GHz and could be overclocked to exceed 4 GHz, which garnered significant attention at the time. However, the official 4 GHz model, which was initially planned for the same architecture, was canceled due to heat and power consumption issues.
The AMD FX-4170 was the first consumer desktop CPU to reach 4 GHz out of the box without any need for overclocking. This chip released in early 2012 clocked at 4.2 GHz from factory, featuring 4 cores and 4 threads, it used the AM3+ socket and had a Thermal Design Power (TDP) rating of 125W. Prior to the FX-4170, AMD had shipped the FX-6200 in December 2011, which came with a standard 3.8 GHz clock that could boost to 4.0 - 4.1 GHz, but it didn't reach the 4 GHz mark at its base frequency.
In 2013, AMD followed up with the Piledriver architecture, which included several chips clocked above 4 GHz. The most prominent of these was the AMD FX-9590, which boasted a base frequency of 4.7 GHz and a turbo frequency of 5.0 GHz, making it the first factory-shipped processor to reach a 5 GHz clock speed. This move was largely seen as an effort to stay competitive against Intel's Core series during that period.
Intel's first consumer processor to be sold with a clock speed of 4 GHz or higher was the Core i7-4790K, launched in 2014 as part of the Haswell Refresh, also known as the "Devil's Canyon" series. This processor was particularly notable for its improved thermal interface material, which allowed for better overclocking headroom – while the company's 2017 Kaby Lake series also had a handful of parts shipped with a stock frequency at or above 4GHz.
A year later, in 2018, Intel celebrated the 40th anniversary of its iconic 8086 processor by launching the limited edition Core i7-8086K. This 6-core/12-thread CPU was Intel's first to reach a 5.0 GHz turbo frequency without overclocking, further solidifying its legacy in the high-performance desktop market.