Intel made some major changes to the processor scene with the release of the Pentium II. They had the PentiumMMX and Pentium Pro's out into the market in a strong way, and they wanted to bring the best of both into one chip. As a result, the Pentium II is kind of like the child of a Pentium MMX mother and the Pentium Pro Father. But like real life, it doesnít necessarily combine the best of itís parents. Pentium II is optimized for 32-bit applications. It also contains the MMX instruction set, which is almost a standard by this time. The chip uses the dynamic execution technology of the Pentium Pro, allowing the processor to predict coming instructions, accelerating work flow. It actually analyzes program instruction and re-orders the schedule of instructions into an order that can be run the quickest. Pentium II has 32KB of L1 cache (16KB each for data and instructions) and has a 512KB of L2 cache on package. The L2 cache runs at Ĺ the speed of the processor, not at full speed. Nonetheless, the fact that the L2 cache is not on the motherboard, but instead in the chip itself, boosts performance.
One of the most noticeable changes in this processor is the change in the package style. Almost all of the Pentium class processors use the Socket 7 interface to the motherboard. Pentium Pro's use Socket 8. Pentium II, however, makes use of "Slot 1". The package-type of the P2 is called Single-Edge contact (SEC). The chip and L2 cache actually reside on a card which attaches to the motherboard via a slot, much like an expansion card. The entire P2 package is surrounded by a plastic cartridge. In addition to Intel's departure into Slot 1, they also patented the new Slot 1 interface, effectively barring the competition from making competitor chips to use the new Slot 1 motherboards. This move, no doubt, demonstrates why Intel moved away from Socket 7 to begin with - they couldn't patent it.
The original Pentium II was code-named "Klamath". It ran at a paltry 66 MHz bus speed and ranged from 233MHz to 300MHz. In 1998, Intel did some slight re-working of the processor and released "Deschutes". They used a 0.25 micron design technology for this one, and allowed a 100MHz system bus. The L2 cache was still separate from the actual processor core and still ran at only half speed. They would not rectify this issue until the release of the Celeron A and Pentium III. Deschutes ran from 333MHz to up to 450 MHz.
About the time Intel was releasing the improved P2's (Deschutes), they decided to tackle the entry level market with a stripped down version of the Pentium II, the Celeron. In order to decrease costs, Intel removed the L2 cache from the Pentium II. They also removed the support for dual processors, an ability that the Pentium II had. Additionally, they ditched the plastic cover which the P2 had, leaving simply the processor on the Slot 1 style card. This, no doubt, reduced the cost of the processor quite a bit, but performance suffered noticeably. Removing the L2 cache from a chip seriously hampers its performance. On top of that, the chip was still limited to the 66MHz system bus. As a result, competitor chips at the same clock speeds could still outperform the Celeron. What was the point?
Intel had realized their mistake with the next edition of the Celeron, the Celeron 300A. The 300A came with 128KB of L2 cache on board. The L2 cache was on-die with the 300A, meaning it ran at full processor speed, not half speed like the Pentium II. This fact was great for Intel users, because the Celerons with full speed cache operated much better than the Pentium II's with 512 KB of cache running at half speed. With this fact, and the fact that Intel unleashed the bus speed of the Celeron, the 300A became well-known in overclocking enthusiast circles. It quickly became known for the cheap chip you could buy and crank up to compete with the more expensive stuff.
The Celeron is available in two formats. The original Celerons used the patented Slot 1 interface. But, Intel later switched over to a PPGA format, or Plastic Pin Grid Array, also known as Socket 370. This new interface allowed reduced costs in manufacturing. It also allowed cheaper conversion from Socket 7 boards to Socket 370. Motherboard manufacturers found it easier to swap out a Socket 7 socket for a Socket 370 socket, more or less leaving the rest of the board the same. It was more involved to change designs over to a slotted board. Slot 1 Celerons ranged from the original 233MHz up to 433 MHz, while Celerons 300MHz and up were available in Socket 370.