I486SX: Difference between revisions
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==Overview== | ==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}} | 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. In support of the theory are additional differences in how the two processors identify themselves with different model numbers (these processors send self-identifying information after reset; an on-demand [[cpuid]] was not invented yet).<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}} | 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}} | {{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 | 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 has no electrical connection; its purpose is to physically prevent the chip from being installed incorrectly ("keying").{{efn|This is not the same as the NC# pin used to shut down the i486SX. NC# is one of the standard 168 pins of the i486, not an extra pin.<ref name="os2museum" /> (NC stands for Not Connect, in the sense of "Do Not Connect". # indicates that it is active on pull-down.))}} The choice of keeping an inactive i486SX is because i486SX was physically hard to remove, being typically installed in non-[[Zero insertion force|ZIF]] sockets or in a plastic package that was surface mounted on the motherboard. Later [[i486 OverDrive]] processors also plugged into the 169-pin socket (since named [[Socket 1]]) 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== | ==Explanatory notes== | ||
Latest revision as of 03:29, 18 June 2025
Template:Short description Template:Multiple image
The i486SX was a microprocessor originally released by Intel in 1991. It was a modified Intel i486DX microprocessor with its floating-point unit (FPU) disabled. It was intended as a lower-cost CPU for use in low-end systems—selling for 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 i386DX, its higher-cost counterpoint), the i486SX was entirely 32-bit.[1]Template:Rp The Intel486 SX-20 CPU can perform up 20 MIPS at 25 MHz while this can also perform 70% faster than the 33 MHz Intel386 DX with external cache.[2]
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 CAD applications, which could often simulate floating point operations in software, but benefited from a hardware floating point unit immensely.[3] AMD had begun manufacturing its i386DX clone, the Am386, which was faster than Intel's.[4] 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.[1]Template:Rp[5]Template:RpTemplate:Efn The i486SX was introduced in mid-1991 at 20 MHz, one core with 8kb of cache in a pin grid array (PGA) package.[3] 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.[6] 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.[1]Template:Rp
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.[7] Initial reviews of the i486SX chip were generally poor among technology publications and the buying public, who deemed it an example of crippleware.[1]Template:Rp Template:Multiple image Many systems allowed the user to upgrade the i486SX to a CPU with the FPU enabled. The upgrade was shipped as the i487, which was a full-blown i486DX chip with an extra pin. The extra pin has no electrical connection; its purpose is to physically prevent the chip from being installed incorrectly ("keying").Template:Efn The choice of keeping an inactive i486SX is because i486SX was physically hard to remove, being typically installed in non-ZIF sockets or in a plastic package that was surface mounted on the motherboard. Later i486 OverDrive processors also plugged into the 169-pin socket (since named Socket 1) and offered performance enhancements as well.[8]
Explanatory notes
References
External links
- Intel 80486SX images and descriptions at cpu-collection.de
- Intel datasheets
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- ↑ a b c d Script error: No such module "Citation/CS1".
- ↑ Intel Corporation, "A Guide to the Intel Architecture", Microcomputer Solutions, January/February 1992, page 11
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- ↑ Intel Corporation, "New Product Focus: Components: Modified Chips Cuts Portable Power Consumption", Microcomputer Solutions, November/December 1991, page 10
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