Affected Models
This problem occurred only on some models of the original Pentium processor. Any Pentium family processor with a clock speed of at least 120 MHz is new enough not to have this bug.
On affected models, the Intel Processor Frequency ID Utility checks for the presence of this bug.
The ten affected processors are listed below. The 39 S-spec of those processors are not listed in the Intel processor specification finder web page.
| Family | Model | Stepping | Core stepping | Clock rate | FSB speed | S-spec |
|---|---|---|---|---|---|---|
| 5 | 1 | 3 | B1 | 60 MHz | 60 MHz | Q0352, Q0412, SX753 |
| 5 | 1 | 3 | B1 | 66 MHz | 66 MHz | Q0353, Q0413, SX754 |
| 5 | 1 | 5 | C1 | 60 MHz | 60 MHz | Q0466, SX835, SZ949 |
| 5 | 1 | 5 | C1 | 66 MHz | 66 MHz | Q0467, SX837, SZ950 |
| Family | Model | Stepping | Core 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, Q0613, Q0543, SX879, SX885, SX909, SX874 |
| 5 | 2 | 1 | B1 | 100 MHz | 66 MHz | Q0563, Q0587, Q0614, SX886, SX910 |
| 5 | 2 | 2 | B3 | 75 MHz | 50 MHz | Q0606, SX951 |
| 5 | 2 | 2 | B3 | 90 MHz | 60 MHz | Q0628, Q0611, Q0612, SX923, SX922, SX921, SX942, SX943, SX944, SZ951 |
| 5 | 2 | 2 | B3 | 100 MHz | 66 MHz | Q0677, SX960 |
The presence of the bug can be checked manually by performing the following calculation in any application that uses native floating point numbers, including the Windows Calculator or Microsoft Excel in Windows 95/98.
The correct value is
However, the value returned by the flawed Pentium is incorrect beyond four digits:
Another way of detecting the bug is using the pentnt utility included with Windows NT 3.51, Windows NT 4.0, Windows 2000, or Windows XP.
Read more about this topic: Fdiv Bug
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