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[ The PC Guide | Systems and Components Reference Guide | The Processor | Processor Families | Fourth Generation Processors ]

Intel 80486DX

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).

Note: 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.

Look here for an explanation of the categories in the processor summary table below, including links to more detailed explanations.

General Information

Manufacturer

Intel, AMD, Cyrix

Family Name

80486DX

Code name

"P4"

Processor Generation

Fourth

Motherboard Generation

Fourth

Version

80486DX-25

80486DX-33

80486DX-50

Introduced

April 1989

May 1990

June 1991

Variants and Licensed Equivalents

80487SX

Speed Specifications

Memory Bus Speed (MHz)

25

33

50

Processor Clock Multiplier

1.0

Processor Speed (MHz)

25

33

50

"P" Rating

--

Benchmarks

iCOMP Rating

122

166

249

iCOMP 2.0 Rating

--

Norton SI

54

72

109

Norton SI32

!?

CPUmark32

--

Physical Characteristics

Process Technology

CMOS

Circuit Size (microns)

1.0

1.0

0.8

Die Size (mm^2)

81

81?

Transistors (millions)

1.2

Voltage, Power and Cooling

External or I/O Voltage (V)

5

Internal or Core Voltage (V)

5

Power Management

SMM in SL-enhanced versions

Cooling Requirements

Generally none, some use passive heat sink.

Packaging

Packaging Style

168-Pin PGA

Motherboard Interface

168-Pin Socket, Socket 1, Socket 2, Socket 3

External Architecture

Data Bus Width (bits)

32

Maximum Data Bus Bandwidth (Mbytes/sec)

95.4

127.2

190.7

Address Bus Width (bits)

32

Maximum Addressable Memory

4 GB

Level 2 Cache Type

Motherboard

Level 2 Cache Size

Usually 0 KB to 256 KB

Level 2 Cache Bus Speed

Same as Memory Bus

Multiprocessing

No

Internal Architecture

Instruction Set

x86

MMX Support

No

Processor Modes

Real, Protected, Virtual Real

x86 Execution Method

Native

Internal Components

Register Size (bits)

32

Pipeline Depth (stages)

5

Level 1 Cache Size

8 KB Unified

Level 1 Cache Mapping

4-Way Set Associative

Level 1 Cache Write Policy

Write-Through

Integer Units

1

Floating Point Unit / Math Coprocessor

Integrated

Instruction Decoders

1

Branch Prediction Buffer Size / Accuracy

None

Write Buffers

None

Performance Enhancing Features

None

Next: Intel 80486SX


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