Gecko's CPU Library

Intel Celeron (Mendocino) processors

Introduction: August 1998


The Celeron brand refered to a range of Intel's x86 CPUs for budget/value personal computers. Considered Intel's "economic" processor, the Celeron branded processors had complemented Intel's higher-performance (and more expensive) brands. Intel had given the brand the motto, "delivering great quality at an exceptional value." Celeron processors was able to run all IA-32 computer programs, but their performance was somewhat lower when compared to similar, but higher priced, Intel CPU brands. For example, the Celeron brand often had less cache memory, or had advanced features purposely disabled. These missing features had a variable impact on performance. In some cases, the effect was significant and in other cases the differences were relatively minor. Many of the Celeron designs had achieved a very high "bang to the buck," while at other times, the performance difference had been noticeable. For example, some intense application software, such as cutting edge PC games, programs for video compression, video editing, or solid modeling (CAD, engineering analysis, computer graphics and animation, rapid prototyping, medical testing, product visualization, and visualization of scientific research), etc. may not performed as well on the Celeron family. This had been the primary justification for the higher cost of other Intel CPU brands vs. the Celeron.

The Mendocino core

The Mendocino Celeron, launched 24 August 1998, was the first mass-market CPU to use on-die L2 cache. Whereas Covington had no secondary cache at all, Mendocino included 128KB of L2 cache running at full clock speed. The first Mendocino-core Celeron was clocked at a then-modest 300MHz but offered almost twice the performance of the old cacheless Covington Celeron at the same clock speed. To distinguish it from the older Covington 300MHz, Intel called the Mendocino core Celeron 300A. Although the other Mendocino Celerons (the 333MHz part, for example) did not have an "A" appended, some people call all Mendocino processors "Celeron-A" regardless of speed.

The new Mendocino core Celeron was a good performer from the outset. Indeed, most industry analysts regarded the first Mendocino-based Celerons as too successful—performance was sufficiently high to not only compete strongly with rival parts, but also to attract buyers away from Intel's high-profit flagship, the Pentium II. Overclockers soon discovered that, given a high-end motherboard, the Celeron 300A could run reliably at 450MHz. This was achieved by simply increasing the Front Side Bus (FSB) speed from the stock 66MHz to the 100MHz spec of the Pentium II. At this speed, the Mendocino Celeron rivaled the fastest x86 processors available.

At the time on-die cache was difficult to manufacture; especially L2 as more of it is needed to attain an adequate level of performance. A benefit of on-die cache is that it operates at the same clock frequency as the CPU. All other Intel CPUs at that time used motherboard mounted or slot mounted secondary L2 cache, which was very easy to manufacture, cheap, and simple to enlarge to any desired size (typical cache sizes were 512KB or 1MB), but they carried the performance penalty of slower cache speed, typically running at FSB speed (60 to 100MHz) for motherboard mounted L2 cache. The implementation of the Pentium II's 512KB of L2 cache was unique at the time (and later copied by AMD's Athlon), comprising moderately high-speed L2 cache chips mounted on a special-purpose board alongside the processor itself, running at half processor speed and communicating with the CPU through a special backside bus. This method of cache placement was expensive and imposed practical cache-size limits, but allowed the Pentium II to be clocked faster and avoided front side bus RAM/L2 cache contention typical with motherboard-placed L2 cache configurations.

Over time, newer Mendocino processors were released at 333, 366, 400, 433, 466, 500, and 533MHz. The Mendocino Celeron CPU came only designed for a 66MHz frontside bus, but this would not be a serious performance bottleneck until clock speeds reached higher levels.

The Mendocino Celerons also introduced new packaging. When the Mendocinos debuted they came in both a Slot 1 SEPP and Socket 370 PPGA package. The Slot 1 form had been designed to accommodate the off-chip cache of the Pentium II and had mounting problems with motherboards. Because all Celerons are a single-chip design, however, there was no reason to retain the slot packaging for L2 cache storage, and Intel discontinued the Slot 1 variant: beginning with the 466MHz part, only the PPGA Socket 370 form was offered. (Third-party manufacturers made motherboard slot-to-socket adapters (nicknamed Slotkets) available for a few dollars, which allowed, for example, a Celeron 500 to be fitted to a Slot 1 motherboard.) One interesting note about the PPGA Socket 370 Mendocinos is that SMP (symmetric multiprocessing) mode was available, and there was at least one motherboard released (the ABIT BP6) which took advantage of this fact.

The Mendocino also came in a mobile variant, with speeds from 266, 300, 333, 366, 400, 433, and 466, 500, 533, 566, 600MHz.

In Intel's "Family/Model/Stepping" scheme, Mendocino CPUs were family 6, model 6 and their Intel product code is 80524. These identifiers were shared with the related Dixon Mobile Pentium II variant.

Source: Wikipedia, the free encyclopedia.