Pentium Flaw Essay
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Pentium Flaw Essay


by Alisha Roberts

Pentium Floating-Point Unit Flaw

4-23-2012

Pentium Flaw

The Pentium floating-point unit flaw only occurred on some models of the original Pentium microprocessor chip. Any of the Pentium family processors with a clock speed of at least 120 MHz is new enough not to have the bug. On the affected microprocessor models, the Intel Processor Frequency ID Utility checks for the floating-point unit flaw. The affected processors are listed below.

Pentium P5 800 nm 5V

Family

Model

Stepping

Manufacturing Stepping

Clock rate

FSB speed

S-spec

5

1

3

B1

60 MHz

60MHz

Q0352

5

1

3

B1

60 MHz

60 MHz

Q0412

5

1

3

B1

60 MHz

60 MHz

SX753

5

1

3

B1

66 MHz

66 MHz

Q0353

5

1

3

B1

66 MHz

66 MHz

Q0413

5

1

3

B1

66 MHz

66 MHz

SX754

5

1

5

C1

60 MHz

60 MHz

Q0466

5

1

5

C1

60 MHz

60 MHz

SX835

5

1

5

C1

60 MHz

60 MHz

SZ949

5

1

5

C1

66 MHz

66 MHz

Q0467

5

1

5

C1

66 MHz

66 MHz

SX837

5

1

5

C1

66 MHz

66 MHz

SZ950

Pentium P54C 600 nm 3.3V

Family

Model

Stepping

Manufacturing Stepping

Clock rate

FSB speed

S-spec

5

2

1

B1

75 MHz

50 MHz

Q0601

5

2

1

B1

90 MHz

60 MHz

Q0542

5

2

1

B1

90 MHz

60 MHz

Q0613

5

2

1

B1

90 MHz

60 MHz

Q0543

5

2

1

B1

90 MHz

60 MHz

SX879

5

2

1

B1

90 MHz

60 MHz

SX885

5

2

1

B1

90 MHz

60 MHz

SX909

5

2

1

B1

90 MHz

60 MHz

SX874

5

2

1

B1

100 MHz

66 MHz

Q0563

5

2

1

B1

100 MHz

66 MHz

Q0587

5

2

1

B1

100 MHz

66 MHz

Q0614

5

2

1

B1

100 MHz

66 MHz

SX886

5

2

1

B1

100 MHz

66 MHz

SX910

5

2

2

B3

75 MHz

50 MHz

Q0606

5

2

2

B3

75 MHz

50 MHz

SX951

5

2

2

B3

90 MHz

60 MHz

Q0628

5

2

2

B3

90 MHz

60 MHz

Q0611

5

2

2

B3

90 MHz

60 MHz

Q0612

5

2

2

B3

90 MHz

60 MHz

SX923

5

2

2

B3

90 MHz

60 MHz

SX922

5

2

2

B3

90 MHz

60 MHz

SX921

5

2

2

B3

90 MHz

60 MHz

SX942

5

2

2

B3

90 MHz

60 MHz

SX943

5

2

2

B3

90 MHz

60 MHz

SX944

5

2

2

B3

90 MHz

60 MHz

SZ951

5

2

2

B3

100 MHz

66 MHz

Q0677

5

2

2

B3

100 MHz

66 MHz

SX960


The presence of the floating-point flaw can be checked manually by performing the following calculation in any application that uses native floating point numbers, including Windows Calculator or Microsoft Excel in Windows 95/98.

The correct value is 419583÷3145727= 1.333820449136241002

The value returned by the flawed Pentium is in correct beyond four significant digits. 419583÷3145727=1.3337390689010357589

There is another way to detect the flaw by using the pentnt utility included with Windows NT 3.51, Windows NT 4.0, Windows 2000, or Windows XP.

In June 1994, Intel discovered the floating-point unit flaw in the Pentium microprocessor. Professor Thomas Nicely, a professor of mathematics at the Lynchburg College, had written code to enumerate primes, twin primes, prime triplets, and prime quadruplets. Professor Thomas Nicely noticed some inconsistencies in the calculations on June 13th , 1994 shortly after adding a Pentium system to his group of computers, but was unable to eliminate other possible factors (such as programming errors, motherboard chipsets, etc.) until October 19, 1994. On October 24th, 1994 he reported the flaw he encountered to Intel. According to Professor Thomas Nicely, the person that he contacted at Intel later admitted to Intel being aware of the flaw since May 1994. The flaw was discovered by Intel during testing of the FPU for its new P6 core, which was first used in the Pentium Pro.

Professor Thomas Nicely sent an email describing the flaw that he had discovered in the Pentium floating point unit (FPU) to various contacts, requesting reports of testing for the flaw on the 486-DX4s, Pentium and the Pentium clones. The flaw in the Pentium FPU (floating-point unit) was quickly verified by other people around the Internet, and became known as the Pentium FDIV bug (FDIV is the x86 assembly language instruction for floating point division). An example of the flaw was found where the division result returned by the Pentium microprocessor was off by about 61 parts per million.

On November 7, 1994 the story first broke in an article published in Electronic Engineering Times, "In the story, Intel says it has corrected the glitch in subsequent runs of the chip, and Steve Smith of Intel dismisses the importance of the flaw, saying, "This doesn't even qualify as an errata (sic)." On November 21, 1994, chief financial correspondent, Steve Young for CNN was the first mainstream media journalist to air the story about the Pentium FDIV flaw and its implications for Intel. The story was later picked up by other national and international media..

On November 30, 1994, Intel released an in-house study of the flaw, "Statistical Analysis of Floating Point Flaw in the Pentium Processor" H.P. Sharangpani and M.L. Barton, Intel Corporation. The study on the Pentium processor minimized the potential impact of the flaw on the majority of the users. On December 12, 1994, IBM decides to do their own study on the Pentium microprocessor chip challenging Intel's analysis and concluding that the FPU flaw will seriously impact the work of a vast majority of users both within and outside the scientific community.

On December 20, 1994, in response to the public's mounting pressure, Intel announces plans for a total recall, replacement and destruction of all the flawed Pentium microprocessors. On January 17, 1995, Intel announces a pre-tax charge of 475 million dollars against their earnings, ostensibly the total cost associated with replacement of flawed microprocessors.

If the same Pentium floating-point unit flaw happened today in today's economy I believe Intel would go under. The government may bail them out of the bankruptcy and that would be only because the majority of the governments computers have a chip made by Intel, but I highly doubt that a bail out would happen because of the upset when the government bailed out the big banks such as Freddie Mack.

Works Cited

Pentium Flaw FAQ. (n.d.). Retrieved April 23, 2012, from trincely: http://www.trnicely.net/pentbug/pentbug.html

Wikipedia, the free encyclopedia. (2012, April 5). Pentium FDIV bug. Retrieved April 20, 2012, from Wikipedia: http://en.wikipedia.org/wiki/Pentium_FDIV_bug

Wolfe, A. (1994, November 7). Intel Fixes A Pentium FPU Glitch. Electronic Engineering Times , 1.


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