After loosing its Lawsuits against AMD, to prevent them from making 486
cpus, Intel decided to abandon number naming of their cpus, because numbers
could not be copyrighted. So the Intel 586 was named Pentium, from 'Penta'
which means 5 in greek and '-ium', used for rare metals names or just like silicium.
It was released in March 1993, in 60 and 66 MHz versions (codename P5), with
a new Socket format, the Socket 4 (273 pins), after several delaying of
release date. Intel told that it was due to process adjusting problems, but
in fact they were not hurried to release it : 486 was widely sold, and they
have no competitors for performances.
Anyway, these versions were completely failed. There was no performance
gain between them and 486DX4-100, they was very expensive and were running
too much hot, making compulsory the use of big heatsink and fans. In a
nutshell, it was not the excellent cpu promised by Intel, and the Socket 4
didn't go further.
One year after, Intel released the second version of the Pentium (codename P54) for a new socket, the socket 5. It was electrically and mechanically completeley different of Socket 4, so upgrade for Pentium 60 (or 66) was impossible. The first model was Pentium 90 which was a really big success. It was exactly the opposite of 60 Mhz models : powerful and not running hot. It was a little expensive but it was better than Pentium 60.
Then came Pentium 100, much more expensive, and Pentium 75, less powerful
but far more cheaper. This last was a big succes in low-end PCs.
However, Intel had a scandal with these versions.
A professor of maths, Dr. Thomas Nicely, discovered that
the round-offs on certain divisions were done incorrectly on Pentium.
60, 66, 75, 90 and 100 MHz versions had the problem.
At first time, Intel denied this, but after they acknowledged and minimized the bug. Then, they were constrained to propose all customers the change of their defect cpus. But they did it too much late, and Pentium got a bad reliability reputation : none would ever completely rely on his calculations on these processors...
We even learned than Intel knew this bug before and had discovered it by developing arithmetic coprocessor of Pentium Pro...
Intel carried on releasing of Pentium in a short time, always or almost two models in the same time : 120 & 133 MHz (March & June 1995), 150 & 166 MHz (January 1996) and then 200 MHz (June 1996).
They were the most powerful cpus ever produced for PCs, and had no rival (AMD and Cyrix were only producing 486 cpus) and were massively sold (except maybe for 150 Mhz version, which was less fast than 166 MHz model, for a quite equivalent price).
Like for 486, Intel released Overdrives, to upgrade 486, old P5, or firsts P54. In the same time, Intel released mobile cpus, very interesting because really very energy efficient and very small (easier to integrate into laptops). Every desktops cpus had a laptop equivalent cpu.
At the beginning of 1997, Intel introduced its new Pentium, which had a set of new x86 instructions, multimedia dedicated, called MMX ((MultiMedia eX tensions), an increase of L1 cache size (from 16 to 32kB), a improved manufacturing process of 0,35µm which made them run cooler. These MMX instructions were principaly used for marketing goals, to have something new against the challengers AMD K5 and Cyrix 6x86. Indeed, applications optimized for MMX came very very late. Though, these 57 new instructions were really interesting, making easier to do vectorial or matricial calculation, often used for video or image processing. Today, every cpus has MMX instructions.
Intel released Pentium MMX at 166, 200 and 233 for desktops computers.
Then, overdrive models for all P54 based computers at 150, 166 and 200MHz.
In the middle of 1997 year, Intel announced Pentium II, and so the end of life of the Pentium.
But mobile versions went further, pushing the P5 architecture to its limit, at 300 MHz, at the beginning of 1999 !!!