The first Pentium Pro was released on November 1st of 1995, and was running at 150MHz.
However, a 133MHz version was officially announced and showed on February, 16th of 1995,
but was never released to market, maybe because Intel wanted to release a Pentium Pro with
greater speed than the biggest one available on Pentium (133MHz at this time).
This cpu was using a full new socket, the Socket 8, not compatible with Socket 7, and with no more than 387 pins count , which was really huge at this time. It used a 0.5µm manufacturing process (later versions have used a 0.35µm process) and had 5500000 transistors,without L2 cache (this one had 15500000 transistors by 256KB cache blocks). The cache was not included in the cpu'core itself, but one another silicium die, intergrated in the ceramic package and directly wire connected with the cpu core (see illustration below).
A Pentium for the "Pro"
When the Pentium Pro was released, some believed that it would replace the Pentium,
and that it would be usable for everyone. Actually it was not, because Intel clearly designed this cpu
for the professional and server market, thing he never did before for any of its cpus (except maybe for the 860).
It was due to 2 things : its price and its performances. The Pentium Pro architecture, which is known as the P6 Architecture (also used for Pentium II and III) was clearly optimised for 32 bits OS, like Windows NT, Linux or OS/2, and less for 16 bits OS or even 16/32 bits OS like Windows 95. Performances of the Pentium Pro on it was below (or in some cases, equals) to those of Pentium of same frequency. On the other hand, on Windows NT, it was really outperforming Pentiums.
Then, cpus' price was very high, because of the big L2 cache amount directly integrated in cpu's package and running at same frequency. Which was never seen before, because previously, L2 cache was integrated in motherboard, and was only 64 or sometimes 128KB, running at bus frequency (66MHz in best case). With pentium Pro, you had a 256 KB - 1MB L2 cache, running between 150 and 200 MHz !
And like some Pentiums, it could work on dual-cpu motherboards. But not only : it was able to run in quad or octo-cpus configurations !
Last point, this cpu didn't have the MMX instructions, which were becoming more and more important for multimedia applications and for games.
In short so, despite the fact it was not a good deal at all for customers (too expensive, no extraordinary performances on Customer's OS), Pentium Pro was an excellent processor for the professionals, and was a first good attempt for Intel to grow on workstations and server market, which was leaded by IBM and Sun until that time.