Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...

's i486SX was a modified Intel

486DX The Intel 486, officially named i486 and also known as 80486, is a microprocessor. It is a higher-performance follow-up to the Intel 386. The i486 was introduced in 1989. It represents the fourth generation of binary compatible CPUs following the ...

microprocessor with its floating-point unit (FPU) disabled. It was intended as a lower-cost CPU for use in low-end systems. Computer manufacturers that used these processors include

Packard Bell Packard Bell is a Dutch-registered computer manufacturing brand and subsidiary of Acer. Originally an American radio set manufacturer, Packard Bell Corporation, it was founded by Herbert A. Bell and Leon S. Packard in 1933. In 1986, Israeli in ...

Compaq Compaq Computer Corporation (sometimes abbreviated to CQ prior to a 2007 rebranding) was an American information technology company founded in 1982 that developed, sold, and supported computers and related products and services. Compaq produced ...

ZEOS Zeos International, Ltd. (stylized as ZEŌS), was a PC manufacturer based in Minneapolis, Minnesota. Originally based in New Brighton, Minnesota, and founded by Gregory E. Herrick, the company incorporated in Minnesota in 1981. Prior to manuf ...

and IBM.

Overview

In the mid-early 1990s, common applications did not need or benefit from an FPU. Among the rare exceptions were

CAD Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve co ...

applications, which could often simulate floating point operations in software, but benefited from a hardware floating point unit immensely. AMD had begun manufacturing its 386DX clone which was faster than Intel's. 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. This was accomplished through a debug feature called Disable Floating Point (DFP), by grounding a certain bond wire in the CPU package. The i486SX was introduced in mid-1991 at 20 MHz in a PGA package. Later (1992) versions of the i486SX had the FPU entirely removed for cost-cutting reasons and comes in surface-mount packages as well. 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 prevents the chip from being installed incorrectly. The NC# pin, one of the standard 168 pins, was used to shut off the i486SX. 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-

ZIF ZIF, ZiF or Zif may refer to: * Zero insertion force Zero insertion force (ZIF) is a type of IC socket or electrical connector that requires very little (but not literally zero) force for insertion. With a ZIF socket, before the IC is inserte ...

sockets or in a plastic package that was surface mounted on the motherboard. Later OverDrive processors also plugged into the socket and offered performance enhancements as well.

Gallery

File:I486sx.jpg, Pin side of an Intel i486 SX File:KL_Intel_i486SX_PQFP.jpg, Embedded i486SX (

SQFP A quad flat package (QFP) is a surface-mounted integrated circuit package with "gull wing" leads extending from each of the four sides. Socketing such packages is rare and through-hole mounting is not possible. Versions ranging from 32 to 304 ...

version). File:Intel i486SX-25.jpg,

BQFP A quad flat package (QFP) is a surface-mounted integrated circuit package with "gull wing" leads extending from each of the four sides. Socketing such packages is rare and through-hole mounting is not possible. Versions ranging from 32 to 304 ...

version.

References

External links

Intel 80486SX images and descriptions at cpu-collection.de
Intel Datasheets
Embedded i486SX

Embedded Ultra-Low Power i486SX
{{Intel processors, discontinued

80486Sx The Intel 486, officially named i486 and also known as 80486, is a microprocessor. It is a higher-performance follow-up to the Intel 386. The i486 was introduced in 1989. It represents the fourth generation of binary compatible CPUs following the ...

de:Intel i486#i486SX