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INTEL INTRODUCES THE 8086 MICROPROCESSOR (APRIL 1978)   



In April 1978, Intel introduced its first 16 bit microprocessor. Production started in May, eventually, the 8086 was officially released on June 8.

The chip had a 28.6 mm² size, was manufactured in NMOS process with 3µm linewidths and contained 29,000 transistors. This was nearly 5x the number of transistors in the earlier 8080, but 200x less than the 5.5 million transistors in a Pentium Pro!

In fact, since the first Intel 4004 processor, the number of transistors in a single chip has been doubling every eighteen months. This exponential rate predicted by Gordon Moore, Intel’s co-founder, is known as the Moore’s law

The 8086 implemented a Complex Instruction Set Computer (CISC) design methodology, and, to improve performance, included a six-byte prefetch queue that was considered a primitive form of pipelining.
It featured twenty address lines giving a total address space of one megabyte. Actually, development team led by Bill Pohlman never suspected anyone would ever need more than one megabyte of RAM. However, the 8086 defines the base architecture of Intel's x86 family which is still in use in actual Intel processors.

The chip also featured a 16 bit data bus allowing a 16 bit value to be read or write in one clock pulse. However, this first version was too expensive to implement in small business computers of the time, so Intel developed an 8 bit data bus compatible version, the 8088. This version was chosen by IBM for the first IBM PC and made Intel the leader of a multi-million dollar industry.
In designing the 8086/8088, Intel chosen to keep an ascending compatibility with its previous 8080 processor, so the memory was not seen as a linear address space, but through 16 segments of 64 KB. This bank-switched architecture will have many negative impacts on PC hardware and software design.
When IBM designed their PC, they assigned ten segments for RAM and the remaining six to other system functions. IBM only started using the true 16 bit 8086 version in the PS/2 model 25 and model 30, in 1987.

First clones of the 8088 and 8086 were respectively the NEC V20 and V30. They had a more efficient design and were slightly faster and efficient, including instructions Intel will later use in its 80186 version.

Intel also released an expensive 8087 math coprocessor which really improved calculation speed for the few programs that supported it.





  
  
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