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Intel Pentium: A Bothersome Bug

Intel's 15 Most Unforgettable x86 CPUs
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The Pentium, introduced in 1993, was interesting for more than one reason. It was the first x86 to drop the traditional model number for a more attractive name, since Intel wasn’t allowed to trademark a name made up of numbers only. It’s also famous because of a bug it contained. On the first generations of Pentiums, certain division operations produced an incorrect result. Intel replaced the processors, but the damage was done. A very rare error gave rise to the first big IT media buzz.

The Pentium was sold in three different versions, the first without a CPU multiplier, the second with a multiplier (including the very familiar Pentium 166), and the last with the SIMD instruction set for x86s, MMX. The Pentium MMX also increased the size of the Level 1 cache and brought in a few minor improvements. This was the first Intel x86 capable of executing two instructions in parallel. The L2 cache was on the motherboard with these processors (running at the frequency of the FSB).

Intel Pentium (MMX)
Code name P5, P54 P55 (Pentium MMX)
Date released 1993 1997
Architecture 32 bits 32 bits
Data bus 64 bits 64 bits
Address bus 32 bits 32 bits
Maximum memory 4096 MB 4096 MB
L1 cache 8 KB + 8 KB 16 KB + 16 KB
L2 cache Motherboard (FSB frequency) Motherboard (FSB frequency)
Clock frequency 60-200 MHz 133-300 MHz
FSB 50-66 MHz 60-66 MHz
FPU on chip on chip
SIMD no MMX
Fabrication process 800-600-350 nm 350 nm
Number of transistors 3.1-3.3 million 4.5 million
Power consumption 8-16 W 4-17 W
Voltage 5 V-3.3 V 2.8 V
Die surface area 294-163-90 mm² 141 mm²
Connector Socket 4, 5 or 7 Socket 7

Here’s a little explanation of the Pentium bug: certain calculations using the FPU resulted in erroneous results. This was fairly rare—though sources disagree about exactly how rare—and Intel replaced the defective processors free of charge. Here’s an example of a Pentium error:

4195835.0/3145727.0 = 1.333 820 449 136 241 002 (correct result) 4195835.0/3145727.0 = 1.333 739 068 902 037 589 (incorrect result on a defective Pentium)

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  • -5 Hide
    Arkz , August 4, 2008 7:19 AM
    great article with only a few slight errors (like saying the core2duo has 1-4 cores... i don't think there's a 1 cored version lol)

    Looking forward to the AMD article.
  • 6 Hide
    aleluja , August 4, 2008 7:36 AM
    To correct you. Core 2 Duo has ONLY 2 cores, not more, not less.
    Core 2 Quad, has 4 cores and Core Solo has 1 core.
  • 3 Hide
    Anonymous , August 4, 2008 7:42 AM
    @Arkz

    Yes there is a singal core,

    http://en.wikipedia.org/wiki/List_of_Intel_Core_2_microprocessors#Single-Core_Mobile_processors

    Ok it is not under the same branding but it is part of the same microarchitecture
  • 1 Hide
    Yuka , August 4, 2008 7:45 AM
    I might be wrong, but i resemble that the Pentium 166 (32bits adress bus and all) had support for 4Gb of memory. I remember IBM sold it's top line (at that time) with 64Mb support (even with SDR PC100/66 support). Correct me if i'm wrong please.
  • -1 Hide
    neiroatopelcc , August 4, 2008 8:39 AM
    The core 2 does supply 1-4 cores - 2 cores per die, where one might be disabled, and one or two dies on a socket. It's no less right to call a core2duo a cpu with 1-4 cores, than it is to put the pentium d on the same page as a single core prescot, as it's the very same principle.
  • -1 Hide
    cangelini , August 4, 2008 9:18 AM
    Arkzgreat article with only a few slight errors (like saying the core2duo has 1-4 cores http://en.wikipedia.org/wiki/Coree ... i don't think there's a 1 cored version lol)Looking forward to the AMD article.


    Thanks for the heads-up! I tweaked that passage to better represent the Core 2 architecture's available configurations!
  • 1 Hide
    randomizer , August 4, 2008 11:03 AM
    vosesterOk it is not under the same branding but it is part of the same microarchitecture

    Exactly. The article says:

    ArticleThere are many versions of the architecture, resulting in configurations with a different number of cores


    There is no mention of the branding, so there is no actual error there, just misinterpretation.
  • 0 Hide
    ImSpartacus , August 4, 2008 11:11 AM
    Arkzgreat article with only a few slight errors (like saying the core2duo has 1-4 cores... i don't think there's a 1 cored version lol)Looking forward to the AMD article.


    http://www.newegg.com/Product/Product.aspx?Item=N82E16819116039

    Yes, it isn't called a "Core 2 Duo," but it uses the Core architecture and only has a single core enabled.

    But I will have to say, there aren't any 3 core models...
  • 4 Hide
    magicandy , August 4, 2008 11:32 AM
    Good to hear you're not only doing an AMD article, but an ATI one as well (in response to the Nvidia article you did earlier, assuming). A sign of class from the new Tom's is a welcome one.
  • 6 Hide
    harrycat88 , August 4, 2008 12:15 PM
    I wish they would get rid of those stupid SNAP Linkbubless and Inteltex misguiding links. Who ever invented those stupid annoying double lined text popups should have been burned at the stake
  • 0 Hide
    JonathanDeane , August 4, 2008 12:39 PM
    What Intelitext do you speak of ? lol (I use a good Hosts file from MVP) blocks most of that crud.

    Anyway great article was like a trip down memory lane for me, first Intel CPU I got to use was a 8086 and wow it was slow (I was a kid with ADD give me a break lol) well maybe it was not slow and it was the floppy drive that killed me... Either way best game on it was Qbasic uugghh I think I remember it having CGA with a mighty 4 colors !! I had some paint program for it too.
  • 0 Hide
    johnlove , August 4, 2008 1:13 PM
    Compared to Athlon, Pentium 4 is a big loser.
    So why is the Pentium 4 "unforgettable"?
  • 0 Hide
    Anonymous , August 4, 2008 1:38 PM
    My AMD machine (K6 233MHz) smoked all my college buddies Pentium 233s. MatLab, Visio, Quattro Pro, PSPICE, Duke Nukem - everything ran faster on my machine. And it cost me $400 less than the comparable Intel setup.
  • 0 Hide
    warezme , August 4, 2008 1:39 PM
    Just 15? I figure its anything with SX after it, anything Celeron and most of anything HT (hyperthreading heat trap)
  • 0 Hide
    warezme , August 4, 2008 1:41 PM
    oops, my dyslexia read the thing as Most Forgettable.., ignore post above. Maybe thats the next article
  • -1 Hide
    jimmysmitty , August 4, 2008 2:02 PM
    johnloveCompared to Athlon, Pentium 4 is a big loser. So why is the Pentium 4 "unforgettable"?


    Because it was a huge part of CPU history? IDK. Considering that it was not that bad until Prescott, which I am sad they didn't mention.

    But the Pentium 4 will always be remembered in my eyes thanks to the Blue Man Group. Them and their crazy stuff.

    theDagdaMy AMD machine (K6 233MHz) smoked all my college buddies Pentium 233s. MatLab, Visio, Quattro Pro, PSPICE, Duke Nukem - everything ran faster on my machine. And it cost me $400 less than the comparable Intel setup.


    Thats nice. Because this is obviously a competition.

    No wait its not. Its just a nice walk down memory lane and they are going to do AMD next so no need for that.

    I for one am suprised that they didn't include the Pentium 805. I remember reading how well that one OCed and when OCed it smoked the highest end available and it only cost $150 bucks.

    Seriously why bring AMD into this? Its just nice memories not a comparison.
  • 0 Hide
    ovaltineplease , August 4, 2008 2:41 PM
    Enjoyed the article, it was a nice walk down memory lane to my teenage nerdhood.
  • 0 Hide
    snarfies1 , August 4, 2008 2:47 PM
    jimmysmittyConsidering that it was not that bad until Prescott, which I am sad they didn't mention.


    If the best you can say about it is "that it was not that bad," that would seem to indicate it wasn't particularly worth remembering.
  • 0 Hide
    Anonymous , August 4, 2008 2:51 PM
    You forgot the 486DX5 133. Allowed me to up a 486/50 to Pentium 75 performance with just a chip. Worked well till programs started to check for a true Pentium chip before running/installing.
  • 0 Hide
    theLaminator , August 4, 2008 3:20 PM
    I've got a working luch box with a 386 in it complete with network cards, Working pentium box, a PIII box, the laptop I still use is a P4 3.0Ghz (an hour and half battery life lol), and my new rig has A core 2 duo E8400 OC'd to 4.0Ghz. Good times for me with Intel
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