Editing I486SX

{{Short description|Type of microprocessor}}
{{multiple image|direction=horizontal|total_width=330px|image1=Intel i486 sx 25mhz 2007 03 27b.jpg|caption1=The Intel i486SX, 25-MHz version|image2=I486sx.jpg|caption2=Pin side of an i486SX}}

The '''i486SX''' was a [[microprocessor]] originally released by [[Intel]] in 1991. It was a modified Intel [[i486|i486DX]] microprocessor with its [[Floating-point unit|floating-point unit (FPU)]] disabled. It was intended as a lower-cost CPU for use in low-end systems—selling for [[United States dollar|US$]]258—adapting the ''SX'' suffix of the earlier [[i386SX]] in order to connote a lower-cost option. However, unlike the i386SX, which had a 16-bit external data bus and a 24-bit external address bus (compared to the fully 32-bit [[i386]]DX, its higher-cost counterpoint), the i486SX was entirely 32-bit.<ref name=Ross />{{rp|117}} The Intel486 SX-20 CPU can perform up 20 MIPS at 25 M[[Hertz|Hz]] while this can also perform 70% faster than the 33 MHz Intel386 DX with external cache.<ref>Intel Corporation, "A Guide to the Intel Architecture", Microcomputer Solutions, January/February 1992, page 11</ref>

==Overview==
In the early 1990s, common applications, such as word processors and database applications, did not need or benefit from a floating-point unit, such as that included in the [[i486]], introduced in 1989. Among the rare exceptions were [[Computer-aided design|CAD]] applications, which could often simulate floating point operations in software, but benefited from a hardware floating point unit immensely.<ref name=Slater>{{cite journal | last=Slater | first=Michael | date=July 1991 | url=https://link.gale.com/apps/doc/A10838604/GPS?sid=wikipedia | title=The new entry-level platform: Intel aims 486SX to gradually replace 386DX | journal=Computer Shopper | publisher=SX2 Media Labs | volume=11 | issue=7 | page=113 | via=Gale}}</ref> [[AMD]] had begun manufacturing its [[i386|i386DX]] clone, the [[Am386]], which was faster than Intel's.<ref>{{cite journal | last=Caron | first=Jeremiah | date=May 20, 1991 | url=https://books.google.com/books?id=18WeIm6AXYoC&pg=PA104 | title=More punch per dollar spent | journal=Computerworld | publisher=IDG Publications | volume=XXV | issue=20 | page=104 | via=Google Books}}</ref> To respond to this new situation, Intel wanted to provide a lower cost [[i486]] CPU for system integrators, but without sacrificing the better profit margins of a full i486. Intel were able to accomplish this with the i486SX, the first revisions of which were practically identical to the i486 but with its floating-point unit internally wired to be disabled.<ref name=Ross>{{cite journal | last=Ross | first=Matthew J. | date=October 13, 1992 | url=https://books.google.com/books?id=F1DQ5qoGN5IC&pg=PA117 | title=486SX: The New Entry-Level PC | journal=PC Magazine | publisher=Ziff-Davis | volume=11 | issue=17 | pages=114–257 | via=}}</ref>{{rp|116–117}}<ref>{{cite journal | last=Seymour | first=Jim | date=December 31, 1991 | url=https://books.google.com/books?id=fb-NRK57wIAC&pg=PT170 | title=486SX: Great for Intel, but What About You? | journal=PC Magazine | publisher=Ziff-Davis | volume=10 | issue=22 | pages=170–238 | via=Google Books}}</ref>{{rp|162–164}}{{efn|A long-standing rumor was that the first batches of the i486SX were i486 chips with defective floating-point units on their dies. However, Alex Witkowski, Intel alumnus and an engineer behind the i486SX, rejected this on the ''OS/2 Museum'' blog, writing that the floating-point units of the original i486 chip die to be converted to i486SX were never tested, and that only by grounding a certain bond wire in the CPU [[Semiconductor package|package]] was this conversion accomplished.<ref name="os2museum">{{cite web|url=http://www.os2museum.com/wp/lies-damn-lies-and-wikipedia/|title=Lies, Damn Lies, and Wikipedia|first=Michal|last=Necasek|work=OS/2 Museum|date=December 26, 2015|access-date=December 27, 2015}}</ref>}} The i486SX was introduced in mid-1991 at 20 MHz, one core with 8kb of cache in a [[Pin grid array|pin grid array (PGA)]] package.<ref name=Slater />  There were low-power version of 16, 20, and 25 MHz Intel486 SX microprocessors.  They were available USD $235, USD $266, and USD $366 for these frequency range respectfully.  All pricing were in quantities of 1,000 pieces.<ref>Intel Corporation, "New Product Focus: Components: Modified Chips Cuts Portable Power Consumption", Microcomputer Solutions, November/December 1991, page 10</ref>  Later versions of the i486SX, from 1992 onward, had the FPU entirely removed for cost-cutting reasons and comes in surface-mount packages as well.<ref name=Ross />{{rp|117}}

The first computer system to ship with an i486SX on its motherboard from the factory was [[Advanced Logic Research]]'s Business VEISA 486/20SX in April 1991.<ref>{{cite journal | last=Lavin | first=Paul | date=April 24, 1991 | url=https://link.gale.com/apps/doc/A10748493/GPS?sid=wikipedia | title=World's first 486SX | journal=PC User | publisher=EMAP Media | issue=157 | page=33 | via=Gale}}</ref> Initial reviews of the i486SX chip were generally poor among technology publications and the buying public, who deemed it an example of [[crippleware]].<ref name=Ross />{{rp|117}}
{{multiple image|direction=horizontal|total_width=330px|image1=KL_Intel_i486SX_PQFP.jpg|caption1=Embedded [[Quad Flat Package|SQFP]] version of the i486SX|image2=Intel i486SX-25.jpg|caption2=[[Quad Flat Package|BQFP]] version of the i486sx}}
Many systems allowed the user to upgrade the i486SX to a CPU with the FPU enabled. The upgrade was shipped as the [[Intel 80487|i487]], which was a full-blown i486DX chip with an extra pin. The extra pin prevents the chip from being installed incorrectly.{{efn|The NC# pin (one of the standard 168 pins of the i486) was used to shut off the i486SX.<ref name="os2museum" />}} Although i486SX devices were not used at all when the i487 was installed, they were hard to remove because the i486SX was typically installed in non-[[Zero insertion force|ZIF]] sockets or in a plastic package that was surface mounted on the motherboard. Later [[Intel OverDrive|OverDrive]] processors also plugged into the socket and offered performance enhancements as well.<ref name=informit>{{cite web | last= | first= | date=June 8, 2001 | url=https://www.informit.com/articles/article.aspx?p=130978&seqNum=28 | title=Microprocessor Types and Specifications | work=InformIT | publisher=Pearson | archiveurl=https://web.archive.org/web/20211207005251/https://www.informit.com/articles/article.aspx?p=130978&seqNum=28 | archivedate=December 7, 2021}}</ref>

==Explanatory notes==
{{Notelist}}

==References==
{{Reflist}}

== External links ==
* [http://www.cpu-collection.de/?l0=co&l1=Intel&l2=i486%20SX Intel 80486SX images and descriptions] at cpu-collection.de
; Intel datasheets
* [http://datasheets.chipdb.org/Intel/x86/486/datashts/27276902.PDF Embedded i486SX]
* [http://datasheets.chipdb.org/Intel/x86/486/datashts/27273101.pdf Embedded Ultra-Low Power i486SX]

{{Intel processors|discontinued}}
{{Lowercase title}}

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[[Category:Intel x86 microprocessors|80486SX]]<!--For the sake of sorting within category-->
[[Category:32-bit microprocessors]]
[[Category:Computer-related introductions in 1991]]

[[de:Intel i486#i486SX]]