The original Celeron was introduced by Intel in response to the company's loss of low-end market share to rival AMD and its K6 processor line. The first Celerons, code-named "Covington", were sold at 266 and 300 MHz speeds and were identical to the Pentium II except that they lacked any level 2 (L2) cache.
The latter characteristic caused the Covington Celerons to be failures in the marketplace. Although they made good processors for computer games because of their powerful floating-point performance, the lack of an L2 cache made them very poor performers in Windows and in business applications.
Several months later, Intel ditched the Covington and introduced the "Celeron-A" based on the "Mendocino" core. This version was identical to the Covington except for the addition of a 128K L2 cache on the processor core. But this one change made the Celeron a hit; enthusiasts soon discovered that the 300 MHz Celeron-A could easily be made to run at 450 MHz simply by increasing the front-side bus speed from the stock 66 MHz to the 100 MHz spec of the Pentium II. At this speed, the Celeron rivaled the fastest available x86 processors in the world.
Intel continued to make the Celeron based on the Deschutes design all the way to 533 MHz, at which point it introduced the "Coppermine-128" core based on the Pentium III in March 2000. This design, which was simply a Pentium III with half the L2 cache, was used well into 2002, with an increase of the bus speed to 100 MHz coming in January of 2001 starting with the 800 MHz part.
The last Celerons based on Pentium III technology, the 1300 and 1400 MHz versions, had a full 256K L2 cache, same as a Pentium III. Intel then jumped the chip up to 1700 MHz and changed the core design to the old Pentium 4 "Willamette" core, with 128K of L2 cache instead of the P4's 256K. These Celerons are considered weak performers by many in the enthusiast market, but are still popular because, like the old 300A, they can run well above their rated speeds.
see also: List of Intel microprocessors