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

Intel 80486DX2 and 80486DX2 OverDrive

The 80486DX2 was the first chip to use "clock doubling" technology, where the processor runs at a faster speed than the memory bus it talks to. This was done to allow the processor speed to be increased without having to deal with the much more difficult task of increasing motherboard speed. Chips that run at faster than memory bus speed improve performance but at a diminishing rate as the multiplier increases, due to the processor waiting for data from memory. This is discussed in detail here.

Intel produced 50 and 66 MHz DX2 chips, intended for use in 25 and 33 MHz system bus systems. These chips have been sold as regular chips intended for use in new systems, which generally come in 168 pin packages to go in the original 168 pin socket used in 486 systems. They have also been made in 169 pin OverDrive versions to go in Socket 1 (the original OverDrive socket). These can be used to upgrade older 486DX or 486SX systems.

AMD and Cyrix not only cloned the 66 MHz DX2 processor, they took Intel one step further with the 80486DX2-80, running at 80 MHz. This uses a 40 MHz system bus, which isn't a speed that is normally used by Intel systems but that became more popular late in the 486 life cycle due to the performance increase it gives over 33 MHz bus systems. In addition, the AMD (enhanced version) and Cyrix chips have several advantages over the Intel chips (they had the benefit of developing them well after Intel):

  • Power Management: They have SMM (power management) built in.
  • Write-Back Cache: They have write-back capability for the primary cache which provides a small boost in performance.
  • Lower Power: They use less power because they run at 3 volts, but will still work in standard 5 volt motherboard sockets without a converter or regulator (they are said to be "5 volt tolerant").

Other than clock speed, the 80486DX2 is virtually identical to the 80486DX. They are obsolete due to the availability of faster, very inexpensive processors such as the 5x86-133 that go in the same sockets, but 486DX2 systems are perfectly viable for many uses, including routine office word processing and spreadsheet work under DOS and Windows 3.x. The 80486DX2-66 is by far the most common version of this chip; a great number of these systems were produced and many are still in use today, especially in small businesses.

Note: The 486DX2 was the first processor to really require a heat sink in order to operate reliably. The increased speed of this chip means that it runs very hot (at least the Intel 5 volt versions).

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

General Information

Manufacturer

Intel

Intel, AMD, Cyrix

AMD, Cyrix

Family Name

80486DX2

Code name

"P24"

 

Processor Generation

Fourth

Motherboard Generation

Fourth

Version

80486DX2-50

80486DX2-66

80486DX2-80

Introduced

March 1992

Aug. 1992

!?

Variants and Licensed Equivalents

--

Speed Specifications

Memory Bus Speed (MHz)

25

33

40

Processor Clock Multiplier

2.0

Processor Speed (MHz)

50

66

80

"P" Rating

--

Benchmarks

iCOMP Rating

231

297

~340

iCOMP 2.0 Rating

--

Norton SI

109

144

173

Norton SI32

~7

~8

~10

CPUmark32

~45

~65

~105

Physical Characteristics

Process Technology

CMOS

Circuit Size (microns)

0.8 (Intel), 0.5 (AMD), 0.65? (Cyrix)

Die Size (mm^2)

76 (Intel)

Transistors (millions)

1.2 (Intel)

Voltage, Power and Cooling

External or I/O Voltage (V)

5 (Intel) 3.3 (AMD, Cyrix, 5V tolerant)

Internal or Core Voltage (V)

5 (Intel), 3.3 (AMD, Cyrix)

Power Management

SMM in AMD, Cyrix, and SL-enhanced Intel versions

Cooling Requirements

Passive or active heat sink

Packaging

Packaging Style

168-Pin PGA (Regular), 169-Pin PGA (OverDrive)

Motherboard Interface

168-Pin Socket (Regular only), Socket 1, Socket 2, Socket 3 (Regular or OverDrive)

External Architecture

Data Bus Width (bits)

32

Maximum Data Bus Bandwidth (Mbytes/sec)

95.4

127.2

152.6

Address Bus Width (bits)

32

Maximum Addressable Memory

4 GB

Level 2 Cache Type

Motherboard

Level 2 Cache Size

Usually 64 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, Write-Back (AMD, Cyrix)

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 80486DX4 and 80486DX4 OverDrive


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