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The Pentium brand refers to Intel's single-core x86 microprocessor based on the P5 fifth-generation micro architecture. The name Pentium was derived from the Greek pente meaning 'five', and the Latin ending -ium.

Introduced on March 22, 1993, the Pentium succeeded the Intel486, in which the number "4" signified the fourth-generation micro architecture. Intel selected the Pentium name after courts had disallowed trade marking of names containing numbers - like "286", "i386", "i486" - though, sometimes, the Pentium is unofficially referred to as i586. In 1996, the original Pentium was succeeded by the Pentium MMX branded CPUs still based on the P5 fifth-generation micro architecture.

Starting in 1995, Intel used the "Pentium" registered trademark in the names of families of post-fifth-generations of x86 processors branded as the Pentium Pro, Pentium II, Pentium III, Pentium 4 and Pentium D. Although they shared the x86 instruction set with the original Pentium (and its predecessors), their micro architectures were radically different from the P5 micro architecture of CPUs branded as Pentium or Pentium MMX. In 2006, the Pentium briefly disappeared from Intel's roadmaps to reemerge in 2007 and solidify in 2008.
Vinod Dham is often referred to as the father of the Intel Pentium processor, although many people, including John H. Crawford (of i386 and i486 alumni), was involved in the design and development of the processor.


Improvements over i486

Pentium Overdrive for i486 systems

Superscalar architecture - The Pentium has two datapaths (pipelines) that allow it to complete more than one instruction per clock cycle. One pipe (called U) can handle any instruction, while the other (called V) can handle the simplest, most common instructions. Some RISC-proponents argued that the "complicated" x86 instruction set would probably never be implemented by a tightly pipelined micro architecture, much less by a dual pipeline design. The 486 and the Pentium demonstrated that this was indeed possible and feasible.

64-bit external data bus width - This doubles the amount of information read or written on each memory access. This doesn't mean that the Pentium can execute 64-bit applications; its main registers are still 32 bits wide.

Faster floating point unit.

MMX instructions (later models only) - A basic SIMD instruction set extension designed for use in multimedia applications.

Pentium architecture chips offered just under twice the performance of a 486 processor per clock cycle. The fastest Intel 486 parts were almost as powerful as a first-generation Pentium, and the AMD Am5x86 was roughly equal to the Pentium 75.

The Pentium ("Classic") series were designed to run at over 100 million instructions per second (MIPS), with the 75 MHz model running at 126.5 MIPS.

reference:
http://en.wikipedia.org/wiki/Pentium