367 WordsApr 22, 20142 Pages

Courtney Bladsacker 1/22/14
Unit 5 Analysis 1: Pentium Flaw
* The problem for Intel is that all Pentiums manufactured until sometime this fall had errors in the on-chip FPU instructions for division.
* The most famous example and the worst well-known case is 4195835/3145727, discovered by Tim Coe of Vitesse Semiconductors
* Intel's policy, when it first publicly admitted the problem around November 28 of 1994, was to replace Pentium chips only for those who could explain their need of high accuracy in complex calculations.
The Pentium microprocessor is the central processing unit for what are now possibly the widest-selling personal computers. Unlike previous CPUs that Intel made, the 486DX and Pentium chips included a floating-point unit FPU. Previous Intel CPUs did all their arithmetic using integers; programs that used floating-point numbers (non-integers like 2.5 or 3.14) needed to tell the chip how to divide them using integer arithmetic. The 486DX and Pentium chips have these instructions built into the chip, in their FPUs. This makes them much faster for intense numerical calculations, more complex, and more expensive. The problem for Intel is that all Pentiums manufactured until sometime this fall had errors in the on-chip FPU instructions for division. This caused the Pentium's FPU to incorrectly divide certain floating-point numbers.
Many software packages, including many that do use floating-point numbers, don't actually use a computer's FPU. These packages don't show the error. Also, only certain numbers whose binary representation shows specific bit patterns divide incorrectly. Consequently many users may never encounter the division error. The most famous example and the worst well-known case is

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