The Intel Celeron processors have been permanently etched into our memories as legends of the overclocking world. When the first Celeron 266 hit the streets, it wasn't long before industrious users attempted to see just how high the core would go. Since Intel has set all Celerons to run on the 66 MHz FSB (front-side bus), this gave some leeway between the Celeron and an equivalent 100 MHz FSB Pentium II CPU. The result of overclocking the C266 was more than likely a 400 MHz chip that provided some exceptional performance gains over the standard 266 MHz core speed. Later on came the Celeron 300, yielding similar overclocking successes.
These cache-less Celeron processors were introduced at a very interesting time. The new Pentium II 350 and 400 had just moved to the new Deschutes core, and Intel determined that by simply removing the 512K of L2 cache they could immediately have an entirely new line of budget CPUs. This was fine in principal, but the low performance scores posted by the Celeron 266 and 300 created a serious black mark against the new budget chip. Business performance was also found to be severely lacking, but 3D game framerates (due to their lower emphasis on the L2 cache) were still very competitive with Pentium II processors of the same speed.
This all changed with the release of the Celeron 300A, which featured a brand new Mendocino core with 128K of fully integrated L2 cache. This design was even a step ahead of the first generation Pentium III processors, but the 66 MHz FSB of the Celeron held it back to budget performance levels. When people started figuring out that a very high percentage of the Celeron 300A, and later C333 and C366, crops would easily make the jump to the 100 MHz FSB, suddenly you could get comparable performance to the Pentium III at a much lower price. The Celeron 300A probably owns the distinction of being the most overclocked CPU ever, and led many a gamer on an elusive hunt for this prized trophy. The Celeron 333 followed, and while most units would reach the 500 MHz core speed, the Celeron 366 and its high probability of reaching 550 MHz received the lion's share of the coverage.
While the Intel Celeron was initially designed to fill the market need for the value-conscious consumer, these processors have actually starting finding their way into quite a few high performance PCs as well. This certainly wasn't Intel's plan, but the promise of a high-speed, low-cost alternative to the Intel Pentium brand processors was just too good to pass up. That is the true essence of overclocking: achieving a level of performance that is much higher than the purchase price would warrant. Overclockers aren't out to have the fastest rig on the block, but they are looking for that special chip that will give them excellent performance, but at a bargain basement price.