Disabled Multipliers on Intel CPUs     When CPU manufacturers make their processors, they usually do this in a similar scenario as the following:  Intel is making Pentium MMX processors.  They setup a production line and make 20 Pentium MMX processors.  They test them according to some conservative standards and only 4 run properly at 233MHz, so the other 16 are set aside and the 4 are marked as Pentium MMX-233s.  Then the remaining 16 are tested for running at 200MHz.  6 pass and the other 10 fail.  The 6 that passed are marked as Pentium MMX-200s and the other 10 are set aside. Now the remaining 10 are tested at 166MHz and 8 pass.  The 8 that passed are marked as Pentium MMX-166s and the other two are thrown away as defective.  Now because Pentium MMX-233s are meant by Intel to run at 66x3.5=233, the 3.5x multiplier is needed for these processors, even though a Pentium MMX-166 is never supposed to use the 3.5x multiplier.  Overclockers realized that since the Pentium MMX-166 had the 3.5x multiplier, they could spend less money by purchasing a Pentium MMX-166 and a really good heatsink & fan unit and then overclocking the Pentium 166 to 200MHz or even 233MHz, than if they had to buy a Pentium MMX-200 or 233 and a regular heatsink & fan.  Although overclocking voided whatever warrantee the processor had, most people could do this successfully, and it is perfectly legal since you bought the processor and can do practically anything with it you want.  You could use it as a $250 hair comb if you wanted.
 
But ever since the days of the Pentium Classic (P54C), Intel has been using a slightly different fabrication process to make versions of their processors that have certain multipliers disabled.  Supposedly Intel does this because they are trying to protect their market share from people who buy a less expensive processor and overclock it to get the performance of a more expensive processor.  However, this most likely deters low-end buyers from buying Intel's processors and overlcocking them and instead buy the already less expensive AMD or Cyrix processors and then probably overclocking them.  Thus, instead of Intel loosing some money from overclocking, they loose alot more money from competition.  As far as I know, AMD and Cyrix have never setup separate fabrication processes for this sinister purpose.  But anyway, so the would be buyer and overclocker of such processors doesn't come home from a computer show only to find that his processor doesn't do what he wanted.  I am providing a list of all processors Intel has made that have certain multipliers disabled and how to tell if yours is one of these or not so that you are able to tell exactly what you're buying should you buy and Intel processor.  (i.e. You should pay less money at a computer show for an Intel processor with the multipliers disabled than for an older one which has all of the multipliers enabled.)
  Tom's Information on the Disabled Multipliers Topic  

Processor	Multipliers Disabled	Distinguishing Features
Intel Pentium Classic 133 (P54C)	2.5x & 3.0x	"I have a P54C-133 which has an S-Spec of S106J, which has the 2.5 & 3.0x multiplier disabled."  "I'm sure that lots of you still remember the Pentium 133 SY022 CPUs, which wouldn't recognize any multiplier setting higher than x2."  (UNDER CONSTRUCTION)
Intel Pentium MMX 166 (P55C)	3x & 3.5x	Pentium MMX-166  Identification Markings.  intel  pentium®  w/ MMXTM tech  A80503166 SZzzz  L722ffff-dddd  INTEL M © '92'95 This identification table was crated  by Chris Hare for the CPU ID page. A80503166 SZzzz                   a.A - Package type                        i. A - Ceramic Pin Grid Array                        ii. BP - Boxed Pentium                        iii. FV - Plastic Pin Grid Array                        iv. TT - Tape Carrier Package                   b. 8050 - Intel Pentium                   c. 3 - Model 3 (Pentium with MMX technology)                   d. 166 - Processor speed                   e. SZzzz - s-Spec identification number   L722ffff-dddd                   a. L - Plant code                   b. 7 - Year of manufacture (1997)                   c. 22 - Week of manufacture (22nd week)                   d. ffff - FPO# (test lot traceability number)                   e. dddd - Serialization code   INTEL (M) © '92'95                   a.'92'95 - Copyright year (not date of manufacture)  The BMD (By Manufacturing Date) method:  Intel started manufacturing Pentium MMX-166s with the 3x and 3.5x multipliers disabled in Mid-July 1997 (27th week of the year). One sure way to get a Pentium MMX-166 that has the 3x and 3.5x multipliers enabled is to buy a boxed version and look at the date on the box sticker (not the price tag).  The date is the day the CPU was packaged.  If the date is before the 27th week of  1997, the 3x and 3.5x multipliers are enabled.  Another way is to check the date stamped on the chip (see above).  If the date is before the 27th week of 1997 (i.e. L726ffff-dddd), then the chip most likely has the 3x and 3.5x multipliers enabled, although I've heard of ones manufactured up to the 30th week and still having them enabled.  The PGA Educated Guess method:  Generally, the ones with the plastic PGA have the 3x and 3.5x multipliers enabled, where as the ones with the ceramic PGA don't, but this isn't always true.  The Manufacturing Info. method:  If the plant code is L, that chip was made in Malaysia, which are supposed to be more overclockable and more likely to have the 3x and 3.5x multipliers enabled than those made in the Philippines, which has the plant code E.  If the s-Spec is SL27H, the serial number begins with L, and the serial number is L7263371-0219 or older, then the chip has the 3x and 3.5x multipliers enabled.  If the s-Spec is SL27H, the serial number begins with L, and the serial number is L7270651-1052 or newer, then it was manufactued using a different fab. process, and the 3x and 3.5x multipliers are disabled.  If the s-Spec is SL27H and the serial number begins with C, then it's from the original fab. process, and the 3x and 3.5x multipliers are enabled.  If the s-Spec is SL27H and the serial number begins with any other letter, your guess is as good as mine.  If you have one of these, I would appreciate you testing for the 3x and 3.5x multipliers and emailing me the results.  If the s-Spec is SL27K, chips manufactured before the 27th week of 1997 (i.e. 87260031-1437) had the 3x and 3.5x multipliers enabled, but later versions (27th week and afterwards) have the 3x and 3.5x multipliers disabled.  If the s-Spec is SY059, as far as I know they all support the 3x multiplier, but only some support the 3.5x multiplier. This is appearantly the result of being manufactured on a line before the 233 was developed. See P200MMX info for details.  Any other s-Specs, your guess is as good as mine.  Please email me if you have a different s-Spec and have tested it.
Intel Pentium MMX 200 (P55C)	3.5x	Pentium MMX- 200  Identification Markings.  intel  pentium®  w/ MMXTM tech  A80503200 SZzzz  L722ffff-dddd  INTEL M © '92'95 This identification table was crated  by Chris Hare for the CPU ID page. A80503166 SZzzz                   a.A - Package type                        i. A - Ceramic Pin Grid Array                        ii. BP - Boxed Pentium                        iii. FV - Plastic Pin Grid Array                        iv. TT - Tape Carrier Package                   b. 8050 - Intel Pentium                   c. 3 - Model 3 (Pentium with MMX technology)                   d. 200 - Processor speed                   e. SZzzz - s-Spec identification number   L722ffff-dddd                   a. L - Plant code                   b. 7 - Year of manufacture (1997)                   c. 22 - Week of manufacture (22nd week)                   d. ffff - FPO# (test lot traceability number)                   e. dddd - Serialization code   INTEL (M) © '92'95                   a.'92'95 - Copyright year (not date of manufacture)  Old Pentium MMX 200s that were manufactured before 233s were (when 200 was top-of-the-line), don't support the 3.5x multiplier since that was designed for the Pentium MMX 233.  One way to tell the old ones from the new is by the manufacturing stepping.  The old ones had a mfg. stepping of xA3 (SL23S/stepping of 4), and the new ones have a mfg. stepping of xB1 (SL27K/stepping of 3).
Intel Pentium II	General	It seems that starting in mid-October 1997, due to extremely high yields (meaning that practically every Pentium MMX produced now is capable of running at 233MHz and every Pentium II produced now is capable of running at 300MHz perfectly fine), Intel is making these processors with their multipliers disabled by not bonding them.  In other words, because all of the CPUs Intel is making now can run at top-of-the-line speed, they are disabling multipliers higher than intended to prevent people from spending less money and overclocking.  Check out Tom's info. for more details.

  How to Identify Intel (and other) Processors Thanks to everybody who's information has made this page possible!