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Central processing units are the brains behind any computer system.This page provides an overview of the 80486DX Central Processing Unit CPU.
 
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Quick Specifications:
Processor Label: 80486DX2 # Of Transistors: 1,180,235
Generation: 4th Generation Cache Memory: 8 KB
Release Year: April 1989 Memory Bus Speed: 25mhz - 50mhz
Data Bus Width: 32 bits Clock Speed Range: 25mhz - 50mhz
Address Bus Width: 32 bits    
More Information:
Picture of this processor.

The Intel 80486DX was the first member of the 486 family (which has many more members than the 386 family did). It provided a very significant increase in power over the 80386DX processor, in fact, far more proportionately than the 386 did over the 286. A 486DX processor provides approximately 100 to 150% more performance than a 386DX of the same clock speed. The 80486 brought GUIs to the mainstream on PCs; it is the minimum processor that most people consider "usable" for running an operating system like Microsoft Windows.

Interestingly, the 486 does not provide its performance improvements by widening any of the buses, as had been the case in the previous two generations: it is still a 32-bit processor with 32-bit data and address buses, just like the 386DX. However, internally, the 486 incorporates several significant improvements over the 386:

  • Faster Overall Instruction Execution time: The core of the chip can execute instructions in less time than earlier processors.
  • Deeper Pipeline: The execution pipeline was increased by one step.
  • Primary Cache: The 486 processor was the first to incorporate level 1 cache on the chip, to reduce the number of required accesses to memory.
  • Integrated Floating Point Unit: The chip includes an integrated math coprocessor (not on the SX version however). In addition, the coprocessor provides much more performance than the optional 80387 used with 386 chips, in part because it is integrated into the chip.
  • Burst Mode: The 486 introduced the use of burst mode to reduce wait time on memory accesses.
  • Power Management: SL power management enhancements as an option (instead of a specialized SL chip as was the case for the 386SL).
  • Improved Support Architecture: In general, 486 motherboards were more efficient than 386 ones, and began to use secondary cache as well. This improves processor performance significantly.

Interestingly, the 80487SX coprocessor that is intended for use with the SX version of the 80486, is in fact a full-blown 80486DX processor. This is part of how Intel structured its fourth generation family's upgrade path. See the description of the 80486SX for more details on this.

AMD and Cyrix did produce clones of the original Intel 80486 processors, but they were not a big player in the 486 clone market until the higher-speed DX2 and DX4 processors.

The 486DX is considered obsolete, although the chip still has fairly good power for performing a wide variety of light tasks, such as word processing and some older games, and light Internet access. The 486DX-50, which runs on a 50 MHz system bus, provides performance comparable to the 486DX2-66 in many ways, because the latter uses only a 33 MHz system bus. The 486DX-50 was not used in nearly as many systems as the other processor speeds were. It should not be confused with the 486DX2-50, which runs at the same processor clock speed but is clock-doubled relative to the system bus (which runs at 25 MHz).

The 486DX processor normally was purchased as part of a new system only, not as part of an upgrade. Most early 486 systems used a 168-pin socket for the chip, which predates the numbered standardized socket system that Intel created. The 486DX will fit into a Socket 1, Socket 2 or Socket 3 however.

 
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