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Enthusiasts have been pushing the limits of silicon for as long as microprocessors have existed. Early overclocking endeavors involved soldering and replacing crystal clock oscillators, but that practice quickly evolved into adjusting system bus speeds using motherboard DIP switches and jumpers.

Internal clock multipliers were eventually introduced, but it didn't take long for those to be locked down, as unscrupulous sellers began removing official frequency ratings and rebranding chips with their own faster markings. System buses and dividers became the primary tuning tools for most users, while ultra-enthusiasts went further – physically altering electrical specifications through hard modding.

Eventually, unlocked multipliers made a comeback, ushering in an era defined by BIOS-level overclocking and increasingly sophisticated software tuning tools. Over the past decade, however, traditional overclocking has become more constrained. Improved factory binning, aggressive turbo boost algorithms, and thermal ceilings mean that modern CPUs often operate near their peak potential right out of the box.

With system bus speeds now tightly controlled to maintain platform stability, most modern overclocking is done through BIOS menus or manufacturer-provided utilities. The challenge has shifted from hardware hacking to managing thermals, navigating firmware quirks, and winning the silicon lottery – but the spirit of overclocking remains alive, driven by those still chasing free performance at the edge of what's possible.

Here's a representative sample of landmark processors revered for their overclocking prowess. Read on!

Note: This TechSpot feature was originally published in December 2014. We continue to update and resurface it periodically because CPU overclocking remains almost as cool today as it was back in the 486DX days

ntel Pentium MMX 166

Release date: January 1997

Stock clock speed: 166MHz

Overclocked: 207 - 266MHz (~54%)

The Pentium MMX arrived amid the height of retailer shadiness and x86 processor vendors responded by locking upper limits for multipliers. As such, many MMXs relied on bus frequency increases for overclocking. Unlocked MMX processors offered more options for overclockers and the unlocked MXX 233 reigned supreme, though its $594 price was prohibitive for many.

At $407, the MMX 166 was a better value, and when paired with a solid 430TX-based motherboard that had a bus speed of 75MHz out of the box, 225 or 266MHz (3 or 3.5 multi) was within reach. To crack 200MHz, MMX 166s with a locked multiplier would need to use the 83MHz jumper setting if available (2.5 * 83 for 207MHz), although stability and heat build-up at this bus speed were far more problematic, as was the sourcing of quality EDO/SDRAM RAM required to run at this frequency.

Intel 486DX2-40

Release date: March 1992

Stock clock speed: 40MHz and 50MHz

Overclocked: 66MHz (~65%)

The P24 DX2 486 processors introduced the CPU clock multiplier, doubling the system bus speed, while the system bus frequency itself was configurable via motherboard jumpers or DIP switches. Initially including 20, 25 and 33MHz options (later augmented by 40 and 50MHz models), users had a path to overclocking that didn't require soldering and replacing the clock crystal oscillator.

Alternatively, you could get the performance of a $799 DX2-66 by purchasing the more modestly priced 486DX2-40 for $400 and raising its default bus speed from 20MHz to 33MHz.

Stability and VLB slot issues at bus speeds over 33MHz meant that overclocking headroom decreased as the base clock rose – to the extent that many Intel DX2-66s wouldn't overclock at all and the few that did were often limited to 80MHz (2 x 40MHz).

AMD K6-2 300 / 350

Release date: May 1998 (300) / August 1998 (350)

Stock clock speed: 300MHz / 350MHz

Overclocked: 400 - 450MHz (~15 – 30%)

Though the K6-2 struggled against Intel's Pentium II and III in raw performance, it was extremely popular among enthusiasts looking to build affordable PCs. The addition of 3DNow! instructions gave it a slight edge in multimedia and gaming workloads that could leverage SIMD.

Enthusiasts with Super Socket 7 motherboards often pushed the 300 and 350MHz models to 400MHz and beyond. While not revolutionary in terms of clock headroom, the K6-2's wide availability, low cost, and tweakability made it a memorable part of the overclocking culture of the late 1990s.

Intel Celeron 300A

Release date: August 1998

Stock clock speed: 300MHz

Overclocked: 375 - 504MHz (~55%)

Think legendary. The Celeron 300A was largely responsible for reigniting mainstream processor overclocking in the late 90's through the ease that it could be accomplished. A 50% overclock to 450MHz was as simple as changing the bus speed from its nominal 66MHz to 100MHz. Although some boards topped out at 83.3MHz limiting the OC to 375MHz, motherboards that supported 103MHz FSB could yield 464MHz.

A better chip with a voltage bump could run at the 112MHz FSB setting to produce 504MHz. Remarkably, the 300A could generally reach 450MHz without any additional voltage requirement over the nominal 2.0 volts. The chip's performance was also aided by having an on-die L2 cache and with a price of $149 it was particularly accessible to system builders.

Also worth mentioning, Intel's Celeron 366 (Mendocino) famously hit 550MHz with a good cooler and a 100MHz FSB. Right after the 300A, it was part of the golden age of overclocking on the cheap

The Most Memorable Overclocking-Friendly CPUs