One Year Ago: Pentium Pro, Pentium II bug warning hits Intel

This story first published May 6, 1997

Reports of a possible new bug in Pentium II and Pentium Pro processors could rain on Intel's parade as the chip giant announces Pentium II later today.

Reported in the x86 Monthly Digest, a Web site dedicated to reporting on Intel, the bug is named "Dan-0411" after its discoverer who e-mailed site editor Robert Collins with his discovery, and the April 11 date he first reported the problem.

The bug concerns the way floating point numbers are converted into integer numbers. According to Collins, "The host software is supposed to be warned by the microprocessor when such a floating point conversion error occurs; a specific error flag is supposed to be set in a floating point status register. If the microprocessor fails to set this flag, it would not be in compliance with the IEEE Floating Point Standards which mandate such behaviour. For the Dan-0411 bug, the Pentium II and Pentium Pro processors fail to set this error flag in many cases."

Collins says he is uncertain as to the importance of the bug but claims the same problem did not occur in tests conducted with Pentium, Pentium MMX and AMD K6 chips, and that the bug isn't reported in any of Intel's errata documents.

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