Intel x86 architecture has evolved over the years. From a 29, 000 transistors microprocessor 8086 that was the first introduced to a quad core Intel core 2 which contains 820 million transistors, the organization and technology has changed dramatically.

Some of the highlights of evolution of x86 architecture are:

1. 8080 –
   It was the world’s first general purpose microprocessor. It was an 8-bit machine, with an 8-bit data path to memory. It was used in the first personal computer.
2. 8086 –
   It was a 16-bit machine and was far more powerful than previous one. It had a wider data path of 16-bits and larger registers along with an instruction cache or queue that prefetches a few instructions before they are executed. It is the first appearance of 8086 architecture. It has a real mode and an addressable memory of 1 MB.
3. 80286 –
   It has an addressable memory of 16 MB instead of just 1 MB and contains two modes-real mode and first generation 16-bit protected mode. It has a data transfer width of 16-bits and programming model of 16-bits (16-bits general purpose registers and 16-bit addressing).
   
   
   
   
4. 80386 –
   It was Intel’s first 32-bit machine.Due to its 32-bit architecture it was able to compete against the complexity and power of microcomputers and mainframes introduced just a few years earlier. It was the first processor to support multitasking and contained the 32-bit protected mode. It also implemented the concept of paging (permitted 32-bit virtual memory address to be translated into 32-bit physical memory address). It has an addressable physical memory of 4 GB and data transfer width of 32-bits.
5. 80486 –
   It introduced the concept of cache technology and instruction pipelining. It contained write protect feature and offered a built in math co-processor that offloaded complex math operations from the main CPU.
6. Pentium –
   The use of superscalar techniques was introduced as multiple instructions started executing in parallel. The page size extension (PSE) feature was added as a minor enhancement in paging.
7. Pentium Pro –
   It used register renaming, branch prediction, data flow analysis, speculative execution and more pipeline stages. Advanced optimization techniques in microcode were also added along with level 2 cache. It implemented the second generation address translation in which 32-bit virtual address is translated into 36-bit physical memory address.
8. Pentium II –
   It was able to process video, audio and graphics data efficiently by incorporating Intel MMX technology (multimedia data set).
9. Pentium III –
   It contains SMD (streaming extensions) instructions (SSE) and supports 3D graphics software. It has a maximum CPU clock rate of 1.4 GHz and contained 70 new instructions.
10. Pentium 4 –
    It implements third generation address translation that translates 48-bit virtual memory address to 48-bit physical memory address. It contains other floating point enhancements for multimedia.
11. Core –
    It is the first Intel microprocessor with dual core that is the implementation of 2 processors on a single chip. There is an addition of Visualizing Technology.
12. Core 2 –
    It extends the architecture to 64-bits and core 2 Quad provides four processors on a single chip. The register set as well as addressing modes are of 64-bits.

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