The Pentium processor was designed by Intel
as the successor to their 486
line, which was itself an extension of the 386
silicon first released in 1985. Due to a loss of a lawsuit against processor manufacturer AMD
, in which it was decided that a number (like 486) could not be considered a copyrighted product name, the processor was named Pentium instead of 586
. This didn't stop AMD
and other chip manufacturers from calling their chips 586's, but combined with the Intel Inside
ad campaign created a stable brand name for Intel, one that they still use today. Market scheduling for the processor was decided by Motorola
's release (and Apple
's use) of the RISC
architecture, which even at lower clock speeds blew the doors off the entire 486 line.
In 1993, the first-generation Pentium processors were released with clock speeds of 60 and 66 MHz. Instead of using the 486's 33 MHz ISA bus to communicate with peripheral devices, the Pentium-supporting chipsets introduced at least the possibility of 66 MHz over Intel's PCI bus, which has become a standard lasting to today. Other improvements included two 8 kilobyte on-die instruction and data caches, additional instructions, superscalar pipelining to execute two instructions simultaneously, and branch prediction to improve pipelining efficiency. Even for a chip that still held compatibility with design features from the 8086 processor released in 1978, it was on the cutting edge. Unfortunately for Intel, the first manufacturing runs of the chip had a bug that made floating point division inaccurate -- this, combined with the chip's (then) unconventional name, made it something of a laughing stock among nerds posting to Usenet and BBS's. The error was quickly corrected and replacement processors shipped, and those who could afford a new system's hefty $3000+ price tag were soon impressed enough to stop giggling.
Those first two speeds (60 and 66 MHz) used the Socket 4 format, which provided the chip 5 volts of power. Notably, the first Pentiums especially were ungodly hot, and it took OEM's some trial-and-error to figure out that they needed attached heat sinks and fans to function without overheating. Socket 5, at 3.3 volts, was released at the beginning of 1995, and by the end of the year one could find processors in 75, 90, 100, 120, and 133 MHz that fit it. This doubling of clock speed (over the course of a couple years, c.f. Moore's Law) was needed for Microsoft's then brand-new Windows 95, which ran hideously slowly on any 486. Finally, Intel began manufacture of Socket 7 motherboards in 1996, which could output between 2.5 and 3.5 volts and supported Pentium processors at 150, 166, and 200 MHz.
1997 saw the last hurrah of the original Pentium line, when Intel released Pentium MMX chips with their new instruction set and dancing technician advertising campaign. MMX instructions gave made the chip able to do single operations simultaneously on multiple sets of data, a method of increasing batch processing speeds that had been pioneered by Cray decades earlier. More information on this is available under MMX, of course. These chips were the last to use any true x86 architecture, which had technically already been superseded by the P6 architecture of 1995's Pentium Pro. Older Socket 7 motherboards couldn't handle the chip's split 2.8/3.3 volt power requirements, which lead to a lot of bitching among upgraders. Pentium MMX chips were released in 166, 200, 233, 266, and 300 MHz models.