The Early Intel Microprocessors
The first microprocessor to appear in the market was the Intel 4004, a 4-bit data bus device.
This device was followed by the 8008, which had an 8-bit data bus.
Two more 8-bit microprocessors (reference to the number of bits usually refers to the data bus
unless stated otherwise), the 8080 and 8085 were introduced in the mid-1970s. These two devices
could address only 216 memory locations.
The 80X86 Family of Microprocessors
Since its introduction in 1978, the so-called X86 architecture has undergo five major
evolutionary stages. The term architecture in relation to microprocessors refers to the internal design
and organization of the device.
The first generation of the 80X86 family includes the 8086, the 8088, and the 80186. Next,
came the 80286, followed by the 80386, and then the 80486. The Pentium is the fifth generation Intel
microprocessor. Each generation built upon the basic concept of the first additional features and
Intel 8086/8088 and 80186
Introduced in 1978, the 8086 was the first 80X86 family and is the basis for all Intel microprocessors that followed.
The 8086 was a 16-bit microprocessor (16-bit data bus) and represented a significant departure from the earlier 8-bit devices.
Owned 20 address lines (allowing 220 memory locations to be accessed).
The various versions of the 8086 operated at clock frequencies of %, 8, or 10MHz.
The 8088 is essentially an 8086 with the 16-bit internal data bus multiplexed down to an 8-bit external bus. It was intended to meet the demand for applications in simpler 8-bit systems and was used in the original IBM personal computer (PC).
The 80186 is an 8086 with several support functions such as clock generator, system controller, interrupt controller, and direct memory access (DMA) controller integrated on the chip. An increased clock frequency of 12.5MHz was added and the 5MHz available in the 8086/8088 was dropped, resulting in a selection of 8, 10, or 12.5MHz.
Introduced in 1982, the memory addressing capability was increased to 24 address lines.
First Intel processor to include an advanced mode of operation (used in the next generations of microprocessors):protected mode. This mode allows access to additional memory locations and advanced programming features.
It operates at the same clock frequencies as the 80186.