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Intel 486SX Microprocessor

While the 80486 (DX version) is basically an enhanced 386 with an internal cache and math coprocessor, the Intel 486SX is the "economy model" lacking the math processor and internal cache. Originally issued as discounted DX chips that failed the cache and/or coprocessor tests, these defective silicon chips were soon released as their own design in a fashion similar to Intel's release of the 386SX following the higher-power 80386 processor (386DX).

View a second image of the Intel 486SX.

Intel squeezed 1.185 million transistors onto a 67-square-millimeter die applying 1.0-micron complementary metal oxide semiconductor (CMOS) fabrication techniques. The Intel 486SX central processing unit (CPU) was released in September 1991 in three models with different clock speeds: 16 MHz, 20 MHz, and 25 MHz versions. All had 32-bit internal registers and external bus widths, could address up to four gigabytes of memory, and maintained backward compatibility with previous CPUs and operating systems. By the following year, Intel released a 33 MHz-clock-speed version with a reduced number of transistors (900,000) using the more advanced 0.8-micron photolithography processes. The newer 486SX-33 MHz was capable of performing 27 million instructions per second (MIPS).

The 486SX microprocessor is referred to by some users as "cripple ware": hardware that is deliberately disabled by the manufacturer and which can supposedly be upgraded to the more expensive model (the 486DX in this case) by some trivial change such as removing a jumper. In fact, many SX owners were the victims of a terrible April Fool's Day prank by a German computer magazine, which reported that by carefully drilling a hole of a specified diameter through the right point on the chip, the disabling circuit would break, reactivating the floating-point unit (FPU). Some people actually attempted this extreme "adjustment" and were then forced to replace their processors. In the case of the initially defective 80486s, Intel used a laser to destroy the FPU connections before shipping them.

Contributing Authors

Omar Alvarado, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.



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