The Pentium Pro was only a partial success for Intel. While it excelled in the server market, it failed as a desktop platform. This was for two reasons:
(1) At the time of its introduction, most users ran 16-bit code and the P-Pro couldn't even keep up with the previous generation (Pentium) chips in this area.
And (2) the Pentium Pro was excessively expensive. This was partially due to the fact that the L2 Cache had to be wired into the CPU package before either the CPU or the Cache could be tested. If one failed, they both had to be thrown away regardless of whether the other was good or not. Fortunately for Intel, the P-Pro core went on to success in the original Celerons, the Pentium II and the Pentium III.

While the MMC-1 module used a PCI interface to connect to the notebook motherboard the MMC-2 (Mobile Module Connector 2) uses an AGP/PCI interface.
The MMC-2 has 10 rows and 400 pins.
On the 266MHz version the L2 cache is not included on the processor die. You see 2 cache RAMs and a controller chip on the backside of the module. The 333MHz version CPU includes the L2 cache.

With the later versions of the 300 MHz Mobile Pentium II Intel moved the L2 cache from the module onto the processor die. The transistor count therefore increased by almost 20 million and the die size doubled.

To reduce costs and provide a more easy way for processor upgrades, the mobile modules were superseded by just the processors packed in small packages. The BGA (Ball Grid Array) was introduced for mobile CPUs and in low-cost notebooks these BGA processors were soldered directly on the mainboard. To make a notebook upgradeable, the BGA processors had to be mounted on adaptors to fit into standardized micro-sockets on notebook mainboards. This CPUs use a BGA package and is soldered on a small PCB with pins to fit into a standard notebook socket. The complete package is called Micro-PGA1 and has 615 pins (243 of them are not connected).

This is an engineering sample of the first Celeron version. It was made in February 1998, some weeks before the official introduction of the Celeron on April 15th, 1998.

» other pre-production sample chips

The first Celeron (codenamed Covington) is essentially a 266MHz Pentium II manufactured without any secondary cache at all. Although clocked at 266 or 300MHz (substantially higher than the old Pentium MMX), the cacheless Celerons are a good deal slower than the parts they were designed to replace. Substantial numbers were sold on first release, largely on the strength of the Intel name, but the Celeron quickly achieved a poor reputation both in the trade press and among computer professionals. Many people referred to it unkindly but accurately enough as the Slugeron, Celery or Deceleron. The initial market interest faded rapidly in the face of its poor performance and with sales at a very low level, Intel felt obliged to develop a substantially faster replacement as soon as possible.

Intel was well aware of the poor reputation of the original Celeron and determined not to make the same mistake twice, with the result that 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.
 
The key to the new Celeron's performance is cache. Where the old model had no secondary cache at all, the new part includes 128KB of L2 cache as part of the chip itself. Otherwise, it is identical. With a total of 19.2 million transistors (including cache) on a single chip, the Mendocino Celeron was difficult and expensive to manufacture, but Intel managed a flawless execution of an ambitious project.
 
The first Mendocino-core Celeron was clocked at a then-modest 300MHz but was almost twice as fast as the old cacheless Celeron at the same clockspeed. To distinguish it from the old model, Intel called it the 300A. Although the other Mendocino Celerons (this 333MHz part, for example) did not have an A appended, some people call all Mendocino processors Celeron-A regardless of speed.

The Mendocino Celerons also introduced new packaging. When the Mendocinos debuted they came in both a Slot 1 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 466 MHz part, only the PPGA Socket 370 form was offered. (Third-party manufacturers made motherboard slot-to-socket adaptors (nicknamed Slockets) available for a few dollars, which allowed, for example, a Celeron 500 to be fitted to a Slot 1 motherboard.)

To reduce costs and provide a more easy way for processor upgrades, the mobile modules were superseded by just the processors packed in small packages. The BGA (Ball Grid Array) was introduced for mobile CPUs and in low-cost notebooks these BGA processors were soldered directly on the mainboard. To make a notebook upgradeable, the BGA processors had to be mounted on adaptors to fit into standardized micro-sockets on notebook mainboards. This CPUs use a BGA package and is soldered on a small PCB with pins to fit into a standard notebook socket. The complete package is called Micro-PGA1 and has 615 pins (243 of them are not connected).

The first Xeon processor was released on June 29, 1998 as the Pentium II Xeon as the replacement of the Pentium Pro. The Pentium II Xeon used either a 440GX (a dual-processor workstation chipset) or 450NX (quad-processor, or oct with additional logic) chipset, and differed from its forerunner in that it had a full-speed, off-die L2 cache. Cache sizes are 512 KB, 1 MB and 2 MB, and it uses a 100 MHz bus.

This processor is still shrink-wrapped in its original box.

Pentium II Xeon (Drake): A Pentium II with full-speed L2 cache.
 
This processor is still shrink-wrapped in its original box.