The Pentium Pro is around now for several years and still it never made it to a best seller as its siblings Pentium, Pentium w/MMX and Pentium II. The main reason for that is and was its weakness with 16 bit code, such as Windows 3.x or Windows 95. The Pentium Pro used to be a clear winner under Windows NT though and there are still a few advantages over the Pentium II in case you want to use it in a high end environment.
The Pentium II's advantages over the Pentium Pro are the additional L1 cache, segment cache registers and MMX extensions. Except of the larger L1 cache the other two features are not improving the Pentium II in high end server environments, but make it more attractive when used under 2nd class operating systems such as Windows 95. The advantage of the Pentium Pro however is the 8 fold larger cacheable area of 4 GB instead of the mediocre 512 MB of the Pentium II, the ability to run in up to quad CPU configurations (PII only dual) as well as its faster L2 cache. You can also get Pentium Pro CPUs with a larger L2 cache than Pentium II CPUs, as long as you pay big bucks for the 1 MB version of the PPro.
Intel's road map has a good reason why it's still placing the Pentium Pro in the high end sector for servers until the Deschutes for Slot 2 is available, because the high end servers want quad CPUs and are not afraid of 4 GB of memory. However it'll be quite a while until Deschutes/Slot2 will be out, before that we'll get Deschutes/Slot1. I'd actually like to take the opportunity and stress again that Slot 2 WILL NOT be the successor of Slot 1, although 99.9% of the second to fourth rate computer websites and magazines seem to tell you that. This includes some big websites as well as some big magazines. The Slot 2 Deschutes will COEXIST to Slot 1, 'Deschutes' stands for nothing else than a Pentium II core that is shrunk to quarter micron size and that runs faster than 300 MHz. The upcoming Pentium II 333/66 will be a 'Deschutes' just as well as the later next year evolving Slot 2 CPU at 400/100 MHz (Intel hasn't picked a name yet). I hope that all the wonnabe computer journalists have got the message now.
Until the Slot 2 CPU will come out, high end servers are either based on really cool CPUs without the Intel logo or a Pentium Pro is working in them. Slot 2 will later next year offer up to 8 CPU configurations, cacheable area up to 4 GB, the L2 cache will be running at CPU core speed and the CPU will run at 100 MHz 'front bus'.
Today you can't equip a Pentium II server with more than 512 MB RAM without a horrible performance loss, since its cacheable area is only 512 MB and if you run it with more you got to disable both caches, L1 as well as L2!!! This results in a perfomance at Pentium 75 niveau. For any high end system requiring over 512 MB of main memory, you still have to chose a Pentium Pro system or wait till next summer. But please be aware of problems with new system architectures. The Pentium II only now has the 440LX chipset to show its performance reserves in combination with SDRAMs, Ultra DMA and AGP, and the first Pentium generation (socket 4, 60/66 MHz, 5 Volts) had to wait for the Neptune Chipset and socket 7 and later for the 430HX to visibly show its much higher performance compared with 486 DX4 CPUs (up to 133 MHz). Furthermore the first generation of new hardware has often been afflicted by bugs or poor performance especially when coming from Intel. Finally the higher price of brand new products quenches many users from buying in the first best moment. So if you need to choose a fast server CPU, don't just negate the Pentium Pro without considering its advantages; today the versions up to 180 MHz can sometimes be obtained quite cheap.