The pentium Pro successor
The pentium II, released in 1998, was directly based on Pentium Pro, a cpu
dedicated to workstations and servers market.
So, for this new cpu generation, Intel had to release a "Pro" product
But unlike the Pentium Pro, Intel didn't make a new cpu, but just adapted their Pentium II to the targetted market, by increasing size and speed of L2 cache and by making them able to handle more than 4 GB of RAM, and making them able to work in 4 or 8-way cpu configurations.
Intel chosen the name of Xeon for this new cpu line.
Pentium II Xeon
The first Xeon, released on June, 29th of 1998, was named Pentium II Xeon, and was running at 400 MHz. It had 512KB L2 Cache, which was running at same speed than the cpu itself, and whose package was a new one, the SECC-330, similar too the SECC-242 of Pentium II, but really bigger. It was particulary dedicated to workstations market. A 1MB L2 Cache version followed, which was more dedicated to servers.
All Pentium II Xeon had a 400 MHz FSB, like latest released Pentium II.Their core was named Drake, and was directly derivated from Deschutes core.
Few models have been released, only 5 actually, with frequencies between 400 and 450 MHz, and with L2 cache between 512KB and 2MB.
They have been quickly replaced by Pentium III Xeons.
Pentium III Xeon
The firsts Pentium III Xeons, with Tanner core (based on Katmai), had a 0,25µm process, where running at 500 and 550 MHz, and were very very similar to Pentium II Xeons, of which they differs almost only from the name.
It wasn't the case of the next ones, the Pentium III Xeons based on Cascades core, which got some of the Pentium III Coppermine improvements (Advanced Transfer Cache, Advanced System Buffering, 133 MHz FSB, SSE), but also lost some of the most important features of Pentium II Xeon and Pentium III Xeon Tanner : big L2 cache of 512KB, 1 ou 2 MB and most of all, the ability of working in 4 and 8-ways configurations (which is mandatory for servers !).
Indeed, their L2 cache was only 256KB (like any Pentium III), and this lack was not compensated at all by the FSB speed increase to 133MHz. And the impossibility to have it in more than 2 cpu configurations, was actually due to the 133MHz FSB.
Intel finally proposed some versions to correct this big lacks, and released 3 models with big L2 cache, 100 MHz FSB and working in 4 and 8-ways configurations. Two of them were running at 700 MHz and had 1 and 2 MB L2 cache, and the third one was running at 900Mhz and had 2MB cache.
Like Pentium II and III, the Pentium II Xeon and Pentium III Xeon, had a
big success, despite the big limitations of most of the models.
With them, Intel managed to really increase their shares in the servers and workstations market, unlike IBM and Sun.
And because of the big popularity they gained from this time, the "Xeon" name is still used nowadays for Intel's professional cpu lines...