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Processor Speed Settings

Notes:

• The jumper settings in the charts below are meant to represent jumper settings on a motherboard. They do not necessarily reflect the state of the multiplier pins (high or low) on the bottom of the processor. See the link at the bottom of the page for the actual multiplier pin settings.
• A pin on the processor which is pulled 'High' is tied to the power plane. A pin which is pulled 'Low' is tied to the ground plane. Pins that are not tied to either the power or ground planes are considered 'floating'.
• BF0, BF1, and BF2 actually refer to multiplier pins on the bottom of a processor. They are not typical jumper names on a motherboard. The jumper will be called something like JP27 or J5 on the motherboard. I used the BF# convention to indicate that there is a corresponding jumper on the motherboard, the name of which will vary depending on the motherboard manufacturer.
• These charts only list theoretical speed settings. They come from the multipliers available on the various chips and the bus speeds present on motherboards.
• The reference clock on modern motherboards usually oscillates at 14.31818MHz for input to the PLL circuit. The PLL then generates a selectable range of bus speed frequencies for the motherboard.

• ¹Pentium OverDrive processors (P24T) have a set multiplier of 2.5x.
• 486 processors which require a 4.0x multiplier use the 2.0x setting.
• Neither DX nor DX2 chips have clock multiplier pins, and so ignore any multiplier setting on the motherboard. An exception is the AMD DX2 Enhanced, which has 2.0x and 3.0x multipliers.
• 33MHz bus speed actually runs at 33.3333... .
• 'Off' is an Open jumper.
  
• 'On' is a Closed jumper.
  

• The AMD K5 has multipliers of 1.5x, 1.75x, and 2.0x. Setting the motherboard to 1.5x or 2.0x will be interpreted by the processor as a 1.5x multiplier. 2.5x is interpreted as 1.75x, and 3.0x becomes 2.0x. This varies depending on the model of the chip. See below for which chips have what multipliers.
• The AMD K6 233 and the Pentium MMX 233 interpret a 1.5x multiplier as 3.5x. 233MHz is the maximum limit for the Intel chip since it does not have a multiplier higher than 3.5x.
• The Model 8 K6-2 CXT, Model 9 K6-3, and Model D K6-2+ and K6-III+ are the only Socket 7 chips with a 6.0x multiplier (it takes the place of the 2.0x multiplier).
• For 4.0x and higher multipliers on the K6, there must be a jumper on the motherboard to set pin BF2 or the chip will default to 'Pulled High', and only give a maximum of 3.5x multiplier. BTW, the AMD K6 does not have a 1.5x multiplier at all.
• The IDT (Centaur) Winchip and Winchip-2 do not have fractional multipliers. The normal 2.5x setting is defined as 'reserved', and the 1.5x setting is interpreted by the chip as 4.0x. When BF2 is added to the motherboard, the typical settings for 4.5x and 5.5x are 'reserved'. 4.0x and 5.0x are unchanged.
• The IDT (Centaur) Winchip-2A adds the unusual 2.33x and 2.66x multipliers in place of the 5.0x and 5.5x settings.
• Default multiplier settings (If the chip receives no signal on its multipliers pins (they're left 'floating'), it reverts to its default setting.):
  • AMD K5 - 1.5x
  • AMD K6/K6-2/K6-3/K6-2+/K6-III+ - 3.5x
  • Cyrix/IBM 6x86/6x86L/6x86MX/M-II - 2.0x
  • Cyrix M-II (later versions w/ CLKMUL2) - 3.0x
  • IDT (Centaur) Winchip/Winchip-2/Winchip-2B - 4.0x
  • IDT (Centaur) Winchip-2A/Winchip-3 - 3.5x
  • Intel Pentium Classic - 1.5x
  • Intel Pentium w/ MMX - 2.0x
  • Rise mP6 - 2.0x
• The 62MHz and 68MHz settings are referred to as a 'turbo frequency'.
• 62MHz actually runs at 62.5MHz.
• 66MHz actually runs at 66.66MHz.
• 68MHz actually runs at 68.66MHz.
• 83MHz actually runs at 83.33MHz.
• 133MHz actually runs at 133.33MHz.
• 'Off' is an Open jumper.
  
• 'On' is a Closed jumper.
  

The following chart lists all of the possible multipliers with each chip and what the motherboard setting is to get that multiplier. To use the chart, look at the top row and find what multiplier you want the chip to have. Then look at the leftside column for which chip. Where they meet on the chart shows what jumper setting(s) on the motherboard to use to achieve that multiplier with that specific chip.

Motherboard Multiplier Settings
AMD	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
AMD K5 SSA5 (Model 0)	1.5x	--	2.0x	--											The one multiplier pin (BF) only gives two options.
AMD K5 5k86 (Model 1)	1.5x 2.0x 2.5x 3.0x	--													Model 1 added another multiplier pin (BF1), but only has a 1.5x multiplier on all of the possible settings.
AMD K5 5k86 (Model 2)	1.5x 2.0x	2.5x	--												Model 2 has both multiplier pins (BF0, BF1), and adds the 1.75x multiplier. I don't know what setting it to 3.0x will yield (probably 1.5x).
AMD K5 5k86 (Model 3)	1.5x 2.0x	2.5x	3.0x	--											Model 3 is rare, but it does exist. Setting the mobo to 3.0x yields 2.0x on the chip (PR200). Has BF0 and BF1.
AMD	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
AMD K6 (Model 6)	--		2.0x	--	2.5x	--	3.0x	--	1.5x 3.5x	--					Has all three multiplier pins (BF0, BF1, BF2), but BF2 apparently is not yet active.
AMD K6 (Model 7)	--		2.0x	--	2.5x	--	3.0x	--	1.5x 3.5x	4.0x	4.5x	5.0x	5.5x	--	Has all three multiplier pins (BF0, BF1, BF2).
AMD K6-2 (Model 8)	--		2.0x	--	2.5x	--	3.0x	--	1.5x 3.5x	4.0x	4.5x	5.0x	5.5x	--	Three multiplier pins (BF0, BF1, BF2). 26050 CPU code.
AMD K6-2 (Model 8 CXT)	--				2.5x	--	3.0x	--	1.5x 3.5x	4.0x	4.5x	5.0x	5.5x	2.0x 6.0x	Three multiplier pins (BF0, BF1, BF2). Adds 6.0x in place of 2.0x. 26351 CPU code.
AMD K6-III (Model 9)	--				2.5x	--	3.0x	--	1.5x 3.5x	4.0x	4.5x	5.0x	5.5x	2.0x 6.0x	Same as K6-2 CXT. Three multiplier pins.
AMD K6-2+ (Model D)	--		2.5x	--			3.0x	--	1.5x 3.5x	4.0x	4.5x	5.0x	5.5x	2.0x 6.0x	Adds 2.0x in place of 2.5x setting. Three multiplier pins.
AMD K6-III+ (Model D)	--		2.5x	--			3.0x	--	1.5x 3.5x	4.0x	4.5x	5.0x	5.5x	2.0x 6.0x	Same as K6-2+. Three multiplier pins.
Cyrix/IBM	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
Cyrix 6x86 (M1)	--		2.0x	--			1.5x	--		3.0x	--				One documented multiplier pin (CLKMUL) and one undocumented (CLKMUL1). Only has whole number multipliers. For 1.0x mode, set to 2.5x.
Cyrix 6x86L (M1L)	--		2.0x	--			1.5x	--		3.0x	--				Same as 6x86. Two multiplier pins.
Cyrix 6x86MX (M2)	1.5x	--	2.0x	--	2.5x	--	3.0x	--							Two multiplier pins (CLKMUL0, CLKMUL1).
Cyrix MII (M2)	--		2.0x	--	2.5x	--	3.0x	--	1.5x 3.5x	--					Two multiplier pins (CLKMUL0, CLKMUL1).
Cyrix MII (later M2: 6-0-1)	--		2.0x	--	2.5x	--	3.0x	--	1.5x 3.5x	4.0x	--				Three multiplier pins (CLKMUL0, CLKMUL1, CLKMUL2).
IDT	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
IDT Winchip (C6)	--		2.0x 2.5x	--			3.0x	--		1.5x 3.5x 4.0x 4.5x	--	5.0x 5.5x	--		Three multiplier pins (BF0, BF1, BF2), but it only has whole number multipliers.
IDT Winchip-2 (C6+)	--		2.0x 2.5x	--			3.0x	--		1.5x 3.5x 4.0x 4.5x	--	5.0x 5.5x	--		Same as Winchip.
IDT Winchip-2A (C6+)	--			5.0x	2.5x	5.5x	3.0x	2.0x	1.5x 3.5x	4.0x	4.5x	--			3 multiplier pins. Adds unusual 2.33x, 2.66x, and 3.33x multipliers.
IDT Winchip-2B (C6+)	--		2.0x 2.5x	--			3.0x	--		1.5x 3.5x 4.0x 4.5x	--	5.0x 5.5x	--		Same as Winchip.
IDT Winchip-3 (C6-2L)	--			5.0x	2.5x	5.5x	3.0x	2.0x	1.5x 3.5x	4.0x	4.5x	--			Same as Winchip-2A.
Intel	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
Intel Pentium (P5 - 60/66)	--														Runs at bus speed. No multiplier pins.
Intel Pentium OverDrive (P5T - 120/133)	--														Runs at 2x bus speed. No multiplier pins.
Intel	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
Intel Pentium Classic (P54C)	1.5x	--	2.0x	--	2.5x	--	3.0x	--							Two multiplier pins (BF0, BF1).
Intel Pentium OverDrive (P54CT)	--				1.5x 2.0x 2.5x 3.0x	--									Fixed 2.5x multiplier. Two useless multiplier pins (BF0, BF1).
Intel	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
Intel Pentium w/ MMX (P55C: 5-4-4)	1.5x	--	2.0x	--	2.5x	--	3.0x	--							Earlier chips with the 5-4-4 stepping. Two multiplier pins (BF0, BF1).
Intel Pentium w/ MMX (P55C: 5-4-3)	--		2.0x	--	2.5x	--	3.0x	--	1.5x 3.5x	--					Later chips with the 5-4-3 stepping. Two multiplier pins (BF0, BF1). Substitutes 3.5x multiplier for 1.5x.
Intel Pentium OverDrive w/ MMX (P54CTB: 5-4-4)	--				1.5x 2.0x 2.5x 3.0x	--									125, 150, 166MHz CPUs. Fixed 2.5x multiplier. Two useless multiplier pins (BF0, BF1).
Intel Pentium OverDrive w/ MMX (P54CTB: 5-4-3)	--						1.5x 2.0x 2.5x 3.0x	--							180 and 200MHz CPUs. Fixed 3.0x multiplier. Two useless multiplier pins (BF0, BF1).
Rise	1.5x	1.75x	2.0x	2.33x	2.5x	2.66x	3.0x	3.33x	3.5x	4.0x	4.5x	5.0x	5.5x	6.0x	Comments
Rise mP6 (step 3.0)	--		2.0x	--	2.5x	--									Two multiplier pins (BF0, BF1).
Rise mP6 (step 4.1b)	--		2.0x	--	2.5x	--	3.0x	--	1.5x 3.5x	--					Two multiplier pins (BF0, BF1).
Notes: 1.) CLKMUL and BF are the same thing. CLKMUL is the Clock Multiplier on Cyrix/IBM chips. BF is the Bus Fraction (or Bus Frequency) on Intel chips. AMD, IDT, and Rise follow Intel's naming convention. 2.) In many cases, the motherboard manual will simply list all of the possible jumper settings with each chip to avoid having to decipher all this nonsense. 3.) Some versions of the Pentium Classic and Pentium w/ MMX chips have had their higher multipliers disabled. See Windwalker's site for more details. 4.) You can use ctcm16r to check the family, model, and stepping of the processor. 5.) If your Intel Pentium w/ MMX chip doesn't seem to be responding to the 3.0x and 3.5x multipliers (and you're sure it isn't a remarked chip), your motherboard may not be sending the correct signal to pin BF0 on the chip. Intel has a page describing the phenomenon. It occurs because Intel redefined the BF0 pin so that it has a pulldown resistor rather than the pullup that the Pentium Classic had. Some motherboard manufacturers may have assumed that the settings were the same, and decided to save a couple of pennies by not having the motherboard properly set the pin. 6.) The step 3.0 Rise mP6 chips have an errata that makes the 3.0x and 3.5x multipliers unusable. This is fixed in stepping 4.1b and later.

• The Pentium Pro and Pentium II processors don't actually have 'BF' pins. Instead, they temporarily use four pins that have other signal descriptions to set the internal bus frequency (BF) at RESET and then hold that value until another active RESET is asserted. The pins used are LINT0 (INTR), IGNNE#, A20M#, and LINT1 (NMI).
• More and more Pentium II systems are coming in jumperless configurations. The bus speeds and multipliers are set through the BIOS rather than with jumpers on the motherboard.
• The newest Pentium III Coppermine and Celeron chips have multipliers beyond those specified using the four pin settings originally defined on the Pentium Pro. Intel either redefined some (all?) of the pin settings or uses the 'Reserved' setting for the needed multipliers on each separate speed rating. Though this point is rather moot considering that Intel locks the multiplier on all their current CPUs; only engineering samples can have their multiplier selected by the motherboard.
• Socket 8 motherboards generally do not have bus speeds higher than 75MHz.
• 66MHz actually runs at 66.66MHz.
• 68MHz actually runs at 68.66MHz.
• 83MHz actually runs at 83.33MHz.
• 133MHz actually runs at 133.33MHz.
• 'Off' is an Open jumper.
  
• 'On' is a Closed jumper.
  

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