# Pentium Flaw Essay

599 Words3 Pages
The Pentium Flaw was originally a problem with the Pentiums microprocessor’s math coprocessor, or floating-point unit (FPU). The Pentium Flaw was discovered at Lynchburg College in 1994 when a math professor, by the name of Thomas Nicely, was calculating sum of reciprocals, using his Pentium computer and noticed that the Pentium calculations were slightly off from the theoretical aspects. He tried another computer and ended up with the correct results and then based the source of the problem on the Pentium itself. He sent an inquiry to Intel about their Pentium flaw, when he received no response he politely posted a notice on the internet if others have confirmed his suspicions. Intel’s response to the flaw was "An error is only likely to occur [about] once in nine billion random floating point divides", and that "an average spreadsheet user could encounter this subtle flaw once in every 27,000 years of use." (Janeba, 1995) What was the flaw in the Pentium Flaw? The article I read on what the Pentium Flaw was said: “The mathematical basis for the bug: The built-in divider in the Pentium FPU uses a radix 4 SRT algorithm. The strength of this algorithm is that it can compute two (binary) digits of a quotient per step, rather than only one per step as in earlier Intel FPU's. The weakness is that the algorithm needs a stored table of values (a "division table", not unlike a "multiplication table"). This table was incorrectly entered into the Pentium FPU -- five entries out of about a thousand were omitted. As in normal long division, at each step in dividing m by n, the Pentium looks at the first few digits of n and of the remainder so far. It uses these as column and row entries in its table to estimate the next few digits of the quotient, then multiplies and subtracts to get the next remainder by the usual method. The table includes negative entries