Intel 80x Processors

Following are short descriptions of Intel CPUs from the 8086 through the 80486:

• Intel 8086
  

  A microprocessor introduced by Intel in 1978. The 8086 chip had a full 16-bit data bus structure.

  While introduced at the same time as the Intel 8088 and was a better processor, the 8086 was not picked for the first IBM personal computers because of the difficulty of building 16-bit accessories versus 8-bit accessories which the 8088 supported.

• Intel 8088
  

  A microprocessor introduced by Intel in 1978. The 8088 chip had a 16-bit internal data bus structure but 8-bit external data bus structure.

  Because of the ease of making 8-bit accessories as opposed to 16-bit accessories, the 8088 was picked to be the microprocessor for the first IBM personal computer as opposed to the 8086.

  The original 8088 operated at 4.77 MHz but was pushed to 10 MHz or more in "turbo" models before the chip was replaced with the next generation of Intel microprocessors. The address space in the chip was a full megabyte, considered a large amount of memory at the time.

• Intel 80286
  

  A microprocessor introduced by Intel in 1984. The 80286 chip had a full 16-bit data bus structure and the address space was increased to 16MB of RAM as the original 8088 1MB address space quickly became crowded.

  The 80286 was introduced to power the IBM Personal Computer AT (Advanced Technology).

  The 80286 microprocessor had a dual personality in that it could run in protected mode where the entire 16MB of memory space was available to the operating system (not MS-DOS) or in real mode where only the 1MB of memory space was available but MS-DOS could be used as the operating system.

• Intel 80386
  

  A microprocessor introduced by Intel in 1986. The 80386 chip had a fill 32-bit data bus structure and the address space was again increased to 4GB.

  One of the revolutions that the 80386 introduces was the ability to divide the memory space into multiple 640KB segments so multiple copies of MS-DOS programs could be run at the same time so long as you had the proper software to manage these memory segments (e.g., DESQview/386 or Windows/386).

• Intel 80386SX
  

  A microprocessor introduced by Intel in 1988. The 80386SX chip was designed to fill a market gap between the 80286 and 80386 which took off slowly. The SX version of the 80386 had all the original chip's capabilities but had a 16-bit external data bus and so could use all of the existing 80286 peripherals.

• Intel 80486
  

  A microprocessor introduced by Intel in 1989. The 80486 was an incremental improvement over the 80386 in that it still had the 32-bit data bus structure but the memory handling increased to 64GB. The 80486 was also the first microprocessor Intel produced which had a numeric coprocessor built into the main chip. With prior CPUs numeric coprocessing chips had to be added to systems that were purchased for mostly number crunching tasks.

  The 80486 was also the first microprocessor that exceeded one million transistors on a single chip.

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