The longevity is partially due to full backwards compatibility and the architecture has also recently been extended to 64-bits, without breaking compatibility. This is now called Intel 64 by Intel (generically called x86-64) and is basically unrelated to the 64-bit IA-64 architecture implemented in Intel's Itanium series.
The IA-32 instruction set is usually described as a CISC (Complex Instruction Set Computer) architecture, though such classifications have become less meaningful with advances in microprocessor design. Modern x86 architectures such as K7, NetBurst, and newer, are often referred to as post-RISC processors.
The IA-32 instruction set was introduced in the Intel 80386 microprocessor in 1985 and remains the basis of most PC microprocessors over twenty years later. Even though the instruction set has remained intact, the successive generations of microprocessors that run it have become much faster. Within various programming language directives, IA-32 is still sometimes referred to as the "i386" architecture.
Intel was the inventor and is the biggest supplier of IA-32 processors, but it is not the only supplier. The second biggest supplier is AMD. There are other suppliers, but their volumes are small. As of 2007, Intel is moving to x86-64, but still produces IA-32 processors such as Celeron M for laptops. VIA Technologies continues to produce the VIA C3/C7 family of "pure" IA-32 devices, and AMD still produces the Geode line and mobile IA-32 processors. For a time Transmeta produced IA-32 processors.
The IA-32 architecture was expanded by AMD in 2003 to natively support 64 bits, creating a new derivative x86-64 architecture. The first family of processors to support this architecture, which AMD calls AMD64, was the AMD K8 family of processors. This was the first time any company other than Intel made significant additions to the IA-32 architecture. Intel was forced to follow suit, introducing modified NetBurst family processors, initially referred to as "IA-32e" or "EM64T" (Enhanced Memory 64 bit Technology) and now called Intel 64 and almost identical to AMD64. x86-64 is backwards compatible with 32-bit code without any performance loss. For example, The Developers Manuals available from Intel on the IA-32 architecture refer to IA-32 and IA-32e in tandem.
The AMD Opteron is the first eighth-generation x86 processor (K8 core), and the first of AMD's AMD64 (x86-64) processors, released April 22, 2003. It is intended to compete in the server market, particularly in the same segment as the Intel Xeon processor.
The Opteron's main advantage is the ability to run existing 32-bit applications without speed penalties, as well as the 64-bit applications that can directly access more than 4 GB of RAM (the physical limit of a 32-bit system).