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Am386

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Template:Short description Template:Infobox CPU

The Am386 CPU is a 100%-compatible clone of the Intel 80386 design released by AMD in March 1991. It sold millions of units, positioning AMD as a legitimate competitor to Intel, rather than being merely a second source for x86 CPUs (then termed 8086-family).<ref name="cpu-collection">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

History and designEdit

File:Amd 386 processor.jpg
Wafer of an Am386 processor with Intel copyright notice
File:AMD 80386DX die.JPG
Die of AMD Am386DX

While the AM386 CPU was essentially ready to be released prior to 1991, Intel kept it tied up in court.<ref name="CPU-World">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Intel learned of the Am386 when both companies hired employees with the same name who coincidentally stayed at the same hotel, which accidentally forwarded a package for AMD to Intel's employee.<ref name="LA Times">Template:Cite news</ref> AMD had previously been a second-source manufacturer of Intel's Intel 8086, Intel 80186 and Intel 80286 designs, and AMD's interpretation of the contract, made up in 1982, was that it covered all derivatives of them. Intel, however, claimed that the contract only covered the 80286 and prior processors and forbade AMD the right to manufacture 80386 CPUs in 1987. After a few years in the courtrooms, AMD finally won the case and the right to sell their Am386 in March 1991.<ref>Template:Cite news</ref> This also paved the way for competition in the 80386-compatible 32-bit CPU market and so lowered the cost of owning a PC.<ref name="cpu-collection" />

While Intel's 386 CPUs had topped out at 33 MHz in 1989, AMD introduced 40 MHz versions of both its 386DX and 386SX out of the gate, extending the lifespan of the architecture. In the following two years the AMD 386DX-40 saw popularity with small manufacturers of PC clones and with budget-minded computer enthusiasts because it offered near-80486 performance at a much lower price than an actual 486.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Generally the 386DX-40 performs nearly on par with a 25 MHz 486 due to the 486 needing fewer clock cycles per instruction, thanks to its tighter pipelining (more overlapping of internal processing) in combination with an on-chip CPU cache. However, its 32-bit 40 MHz data bus gave the 386DX-40 comparatively good memory and I/O performance.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

  • KL AMD 386DX.jpg

    An Am386DX-25

  • KL AMD Am386DE.jpg

    The Am386DE-33 is an embedded version of the Am386DX-33.

  • AMD Am386DX DXL.jpg

    A PGA Am386DX-40

  • AMD Am386 DX-40 2007 03 27.jpg

    A PQFP Am386DX-40 on a 132-pin PGA adapter

  • AMD Am386DE Block Diagram.tif

    AMD Am386DE block diagram. There is not a Paging Unit like a DX CPU.

  • Early Nineties 386DX-40.png

    A scan of an AMD Am386™DX-40 mounted on a PGA adapter

Am386DX dataEdit

The various models of the Am386DX, data from<ref name="cpu-collection" /><ref name="CPU-World" />
Model number Frequency FSB Voltage Power Socket
AMD Am386DX/DXL-20 20 MHz 5 V 1.05 Watt 132-pin CPGA
AMD Am386DX/DXL-25 25 MHz 1.31 Watt
AMD Am386DX/DXL-33 33 MHz 1.73 Watt
AMD Am386DX/DXL-40 40 MHz 2.10 Watt
AMD Am386DX-40 3.03 Watt 132-pin PQFP
AMD Am386DXLV-25 25 MHz 3-5 V 445 mW (at 3.3V) 132-pin PQFP,<ref name="amd1992_386book">AMD, Personal Computer Microprocessors Data Book, 1992 - see pages 436-444 for information on Am386DXLV and pages 459-467 for information on Am386SXLV.</ref>
132-pin PGA<ref name="wharton1994"/>
AMD Am386DXLV-33 33 MHz 5 V 1.65 Watt

Am386DE dataEdit

  • 32-bit data bus, can select between either a 32-bit bus or a 16-bit bus by use of the BS16 input
  • 32-bit physical address space, 4 Gbyte physical memory address space
  • fetches code in four-byte units
  • no paging unit<ref name="mpr_386de">Microprocessor Report, Vol.8, No.3, March 7, 1994, "Most Significant Bits", pages 1-2</ref>
The various models of the Am386DE, data from<ref name="cpu-collection" /><ref name="CPU-World" />
Model number Frequency FSB Voltage Power Socket Release date
AMD Am386DE-25KC 25 MHz 3-5 V 0.32-1.05 Watt 132-pin PQFP 1994<ref name="mpr_386de"/>
AMD Am386DE-33KC 33 MHz 5 V 1.05-1.35 Watt
AMD Am386DE-33GC 132-pin CPGA

AM386 SXEdit

In 1991 AMD also introduced advanced versions of the 386SX processor – again not as a second source production of the Intel chip, but as a reverse engineered pin compatible version. In fact, it was AMD's first entry in the x86 market other than as a second source for Intel.<ref name="cpu-collection-SX">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> AMD 386SX processors were available at higher clock speeds at the time they were introduced and still cheaper than the Intel 386SX. Produced in 0.8 μm technology and using a static core, their clock speed could be dropped down to 0 MHz, consuming just some mWatts. Power consumption was up to 35% lower than with Intel's design and even lower than the 386SL's, making the AMD 386SX the ideal chip for both desktop and mobile computers. The SXL versions featured advanced power management functions and used even less power.<ref name="cpu-collection-SX" />

  • Am386SXL-25cropped.jpg

    An Am386SX-25

  • KL AMD 386SX.jpg

    An Am386SX-33

  • Ic-photo-AMD--Am386SX-40--(NG80386SX-40)--(386-CPU).png

    An Am386SX-40

Am386SX dataEdit

  • 16-bit data bus, no bus sizing option
  • 24-bit physical address space, 16 Mbyte physical memory address space
  • prefetch unit reads two bytes as one unit (like the 80286).
The various models of the Am386SX, data from<ref name="CPU-World" /><ref name="cpu-collection-SX" /><ref name="AMD Am386 Microprocessors for Personal Computers Datasheet">[1] Template:Webarchive, AMD Datasheet no 15022.</ref>
Model number Frequency FSB Voltage Power Socket Release date
AMD Am386SX/SXL-20 20 MHz 5 V 1.68/0.85 Watt 100-pin PQFP 1991
AMD Am386SX/SXL-25 25 MHz 1.84/1.05 Watt 29 April 1991
AMD Am386SX/SXL-33 33 MHz 1.35 Watt 1992
AMD Am386SX-40 40 MHz 1.55 Watt 1991
AMD Am386SXLV-20 20 MHz 3-5V 100-pin PQFP<ref name="amd1992_386book"/> October 1991<ref name="wharton1994"/>
AMD Am386SXLV-25 25 MHz 412 mW (at 3.3V)<ref name="wharton1994"/>

Am386SE dataEdit

  • 16-bit data bus, no bus sizing option
  • 24-bit physical address space, 16 Mbyte physical memory address space
  • prefetch unit reads two bytes as one unit (like the 80286).
  • no paging unit<ref name="mpr_386de"/>
The various models of the Am386SE, data from<ref name="am386se_datasheet">AMD, Am386SE High Performance, Low-Power, 32-bit Embedded Microprocessor, pub.no. 18420, rev B, June 1994, see page 7 for product list and pages 60-61 for DC characteristics. Archived on 25 Jan 2025.</ref>
Model number Frequency FSB Voltage Socket Release date
AMD Am386SE-25KC 25 MHz 3-5 V 100-pin PQFP 1994<ref name="mpr_386de" />
AMD Am386SE-25KI
AMD Am386SE-25VC 100-pin TQFP
AMD Am386SE-25VI
AMD Am386SE-33KC 33 MHz 5 V 100-pin PQFP

Embedded Am386 processorsEdit

Template:See also The Am386 processor core has been used in some embedded processors. In October 1993, AMD introduced the Am386SC processor, which integrated an Am386SXLV CPU core with a collection of PC/AT-compatible peripherals.<ref>Microprocessor Report, AMD’s Elan Puts 386 PC in Pocket (vol 7, no. 14, October 25, 1993). Archived on 22 Apr 2024.</ref> This processor, marketed as "Élan SC300" and "Élan SC310", was the first in AMD's Élan series of SoCs. In 1994, AMD announced the Am386EM microcontroller, which integrated an Am386 CPU core with a collection of 80186-compatible peripherals rather than PC/AT peripherials.<ref>Microprocessor Report, Most Significant bits (vol 8, No. 13, October 3, 1994), page 3. Archived on 22 Apr 2024.</ref><ref>Tech Monitor, Advanced Micro Creates iAPX-86 Microcontrollers, 26 Sep 1994. Archived on 26 Jan 2025.</ref> This chip does not, however, appear to have been released,<ref>R. Oestergaard, What comes after 80186?, 14 dec 1995, comp.arch.embedded newsgroup post. Archived on 26 Jan 2025.</ref> although a datasheet exists.<ref>AMD, Am386EM 386-Based 80C186/8-Compatible 32-bit Embedded Microcontroller, pub.no. 19167, rev A, august 1994. Archived on 25 Jan 2025.</ref>

80387 coprocessorEdit

Floating point performance of the Am386 could be boosted with the addition of a 80387DX or 80387SX coprocessor, although performance would still not approach that of the on-chip FPU of the 486DX. This made the Am386DX a suboptimal choice for scientific applications and CAD using floating point intensive calculations. However, both were niche markets in the early 1990s and the chip sold well, first as a mid-range contender, and then as a budget chip. Although motherboards using the older 386 CPUs often had limited memory expansion possibilities and therefore struggled under Windows 95's memory requirements, boards using the Am386 were sold well into the mid-1990s; at the end as budget motherboards for those who were only interested in running MS-DOS or Windows 3.1x applications. The Am386 and its low-power successors were also popular choices for embedded systems, for a much longer period than their life span as PC processors.

  • KL IIT 3C87SX.jpg

    An IIT 387SX-25 Coprocessor

  • FasMath.jpg

    A Cyrix FasMath 387DX-33 Coprocessor

  • KL ULSI US83S87SX SLC.jpg

    An ULSI 387SX-40 Coprocessor

ReferencesEdit

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External linksEdit

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