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Mixing Processor Steppings



Mixing processor steppings (revisions) in a dual environment doesn't always work as well as it should. As a rule of thumb, one stepping difference between two CPUs is generally acceptable. Two steppings is pushing it. Note that some revisions of some operating systems may be more forgiving than others (like WinNT) concerning mixed steppings. The motherboard manufacturer can also give you information about which mixed steppings (if any) are compatible with the motherboard. It's always best to buy matched pairs or to find another chip with the same S-Spec number. Although in many cases, finding an identical chip is quite difficult.

Intel Pentium

Pentium Classic and Pentium w/ MMX processors are designated as '0', '2', or both. Chips with a '0' designation can be used alone or as the primary processor in a dual environment. Those with the '2' designation can only function as secondary processors in a dual environment (they also have the 'DP' designation in the charts). Those with both designations can function as either. See Intel's Pentium Quick Reference Guide for which chips have which designations. Processors listed with comment number 8 do not support DP, FRC, or APIC and cannot function in a dual environment. The information in these charts comes from the Pentium Specification Update which requires the Adobe Acrobat Reader to view it.

On the bottom of the Pentium Classic chips, there is a three letter mark such as: 'SSS'. The last letter indicates whether the chip was tested for dual-processing or not. The letter 'S' indicates the chip was tested for dual-processing, uni-processing and multi-processing. A chip with the letter 'U' means the chips was tested for uni-processing and multi-processing, but not dual-processing. The Pentium w/ MMX chips do not have this lettering system since all P55C chips (except the mobile and OverDrive versions) are capable of dual processing.

BTW, neither Pentium OverDrive processors nor mobile processors support APIC, and cannot be used as upgrades in a dual processor environment. The Pentium Pro OverDrive is the exception to this rule. This chip can run in a dual configuration.

See Mixing Pentium Steppings for Pentium and Pentium with MMX processors.



Intel Pentium Pro

Pentium Pro chips should be as closely matched as possible. Although some motherboards may be more forgiving than others, the less variance the better. Notice that some chips run at 3.5v while most run at 3.3v. If your system was designed to run both chips with one voltage regulator, you would need to match the chip voltages. Although some motherboards may require a separate VRM (voltage regulator module) for the new processor regardless. Check with the manufacturer. The original chip will have an sSpec identification number written on it (such as SL23M). Finding another chip with the same sSpec on it is the ideal situation. But this is often impossible to do. In that case, the chip's stepping should be as close as possible. You can check the stepping of your CPU by using Intel's CPUID program. It will give you the Family, Model, and Stepping. Then download Intel's Pentium Pro Specification Update to try to find a CPU that matches. Unfortunately, most of the ones floating around now are stepping 9, which isn't close enough to the other existing steppings. And any chips with earlier steppings you may find are undoubtedly used processors. Of course, you could always just buy two new chips! :-/

Taken from the Intel Pentium Pro Specification Update PDF file:
Pentium Pro
Stepping
150MHz
B0
(6-1-1)
150MHz
C0
(6-1-2)
166, 180,
200MHz sA0
(6-1-6)
166, 180,
200MHz sA1
(6-1-7)
166, 180,
200MHz sB1
(6-1-9)
OverDrive
Processor
150MHz B0
(6-1-1)
331,31,31,3X
150MHz C0
(6-1-2)
331,31,31,3X
166, 180, 200MHz sA0
(6-1-6)
1,31,3333X
166, 180, 200MHz sA1
(6-1-7)
1,31,33NINIX
166, 180, 200MHz sB1
(6-1-9)
1,31,33NINIX
OverDrive ProcessorXXXXX2


  1. The 150MHz and the 166, 180, and 200MHz parts vary in their GTL+ TCO_MIN and THOLD timings by 250ps. This may affect some system designs. Also, a customer may wish to use a higher frequency replacement for a 150MHz system; this should also be considered.
  2. OverDrive processor upgrades for the Pentium Pro processor will only be supported in one and two processor systems, and are only supported in same stepping configurations.
  3. Errata numbers 39 and 41 may be problematic for 3- or 4-way MP systems which use processor steppings previous to the sA1 stepping.

Also see the Multiprocessor Specification.



Intel Pentium II/III

For dual Pentium II processors to be used in a motherboard, the CPUs must run at the same bus and core speed, use the same voltage, and have the same L2 cache size and characteristics.

A BIOS upgrade may be necessary to get two chips to work in tandem (it supplies any needed microcode updates). It can also help with voltage detection.

Older Pentium II processors (code-named Klamath at 233, 266, and 300MHz) run on a 2.8v core voltage while newer chips (Deschutes running at 266 up through 450MHz) function at 2.0v. These CPUs may not be compatible in the same board unless you install a separate VRM (voltage regulator module) for the secondary processor. Contact the motherboard manufacturer for details.

Even though it is based on the Pentium II core, the Intel Celeron processor does not officially support dual-processing.

The 370-pin FC-PGA Pentium-III Coppermine chips with a 6-8-1 stepping are not dual capable.

The 6-8-3 step (cB0) Slot 1 1GHz Pentium-III Coppermine chips are not dual capable. Neither is the 1.13GHz Slot 1 Pentium III chip, which was recalled.

Taken from the Intel Pentium II Specification Update PDF File:
66MHz
Pentium II
Stepping
233
C0
(6-3-3)
266
C0
(6-3-3)
300
C0
(6-3-3)
233
C1
(6-3-4)
266
C1
(6-3-4)
300
C1
(6-3-4)
266
dA0
(6-5-0)
333
dA0
(6-5-0)
300
dA1
(6-5-1)
333
dA1
(6-5-1)
266
dB0
(6-5-2)
300
dB0
(6-5-2)
333
dB0
(6-5-2)
233 C0 (6-3-3)1XX1XXXXXXXXX
266 C0 (6-3-3)X1XX1X1XXX1XX
300 C0 (6-3-3)XX1XX1XX1XX1X
233 C1 (6-3-4)1XXNIXXXXXXXXX
266 C1 (6-3-4)X1XXNIXNIXXXNIXX
300 C1 (6-3-4)XX1XXNIXXNIXXNIX
266 dA0 (6-5-0)X1XXNIXNIXXXNIXX
333 dA0 (6-5-0)XXXXXXXNIXNIXXNI
300 dA1 (6-5-1)XX1XXNIXXNIXXNIX
333 dA1 (6-5-1)XXXXXXXNIXNIXXNI
266 dB0 (6-5-2)X1XXNIXNIXXXNIXX
300 dB0 (6-5-2)XX1XXNIXXNIXXNIX
333 dB0 (6-5-2)XXXXXXXNIXNIXXNI

  1. Errata numbers 16 and 17 may be problematic for DP systems which use Pentium II processor, model 3 C0 stepping.

100MHz
Pentium II
Stepping
350
dA0
(6-5-0)
350
dA1
(6-5-1)
400
dA1
(6-5-1)
350
dB0
(6-5-2)
400
dB0
(6-5-2)
450
dB0
(6-5-2)
350
dB1
(6-5-3)
400
dB1
(6-5-3)
350 dA0 (6-5-0)NINIXNIXXNIX
350 dA1 (6-5-1)NINIXNIXXNIX
400 dA1 (6-5-1)XXNIXNIXXNI
350 dB0 (6-5-2)NINIXNIXXNIX
400 dB0 (6-5-2)XXNIXNIXXNI
450 dB0 (6-5-2)XXXXXNIXX
350 dB1 (6-5-3)NINIXNIXXNIX
400 dB1 (6-5-3)XXNIXNIXXNI

Also see: Pentium II Integration Notes.


Taken from the Intel Pentium III Specification Update PDF File:
100MHz Slot 1
Pentium III
Stepping
450
kB0
(6-7-2)
450
kC0
(6-7-3)
500
kB0
(6-7-2)
500
kC0
(6-7-3)
550
kC0
(6-7-3)
600
kC0
(6-7-3)
450 kB0 (6-7-2)NINIXXXX
450 kC0 (6-7-3)NINIXXXX
500 kB0 (6-7-2)XXNINIXX
500 kC0 (6-7-3)XXNINIXX
550 kC0 (6-7-3)XXXXNIX
600 kC0 (6-7-3)XXXXXNI
100MHz Slot 1
Pentium III
Stepping
550E
cB0
(6-8-3)
600E
cA2
(6-8-1)
600E
cB0
(6-8-3)
600E
cC0
(6-8-6)
650
cA2
(6-8-1)
650
cB0
(6-8-3)
650
cC0
(6-8-6)
700
cA2
(6-8-1)
700
cB0
(6-8-3)
700
cC0
(6-8-6)
750
cA2
(6-8-1)
750
cB0
(6-8-3)
750
cC0
(6-8-6)
550E cB0 (6-8-3)NIXXXXXXXXXXXX
600E cA2 (6-8-1)XNININIXXXXXXXXX
600E cB0 (6-8-3)XNININIXXXXXXXXX
600E cC0 (6-8-6)XNININIXXXXXXXXX
650 cA2 (6-8-1)XXXXNININIXXXXXX
650 cB0 (6-8-3)XXXXNININIXXXXXX
650 cC0 (6-8-6)XXXXNININIXXXXXX
700 cA2 (6-8-1)XXXXXXXNININIXXX
700 cB0 (6-8-3)XXXXXXXNININIXXX
700 cC0 (6-8-6)XXXXXXXNININIXXX
750 cA2 (6-8-1)XXXXXXXXXXNININI
750 cB0 (6-8-3)XXXXXXXXXXNININI
750 cC0 (6-8-6)XXXXXXXXXXNININI
100MHz Slot 1
Pentium III
Stepping
800
cA2
(6-8-1)
800
cB0
(6-8-3)
800
cC0
(6-8-6)
850
cB0
(6-8-3)
850
cC0
(6-8-6)
1.0
cC0
(6-8-6)
800 cA2 (6-8-1)NININIXXX
800 cB0 (6-8-3)NININIXXX
800 cC0 (6-8-6)NININIXXX
850 cB0 (6-8-3)XXXNINIX
850 cC0 (6-8-6)XXXNINIX
1.0 cC0 (6-8-6)XXXXXNI

133MHz Slot 1
Pentium III
Stepping
533B
kB0
(6-7-2)
533B
kC0
(6-7-3)
533EB
cA2
(6-8-1)
600B
kC0
(6-7-3)
600EB
cA2
(6-8-1)
600EB
cB0
(6-8-3)
600EB
cC0
(6-8-6)
667
cA2
(6-8-1)
667
cB0
(6-8-3)
667
cC0
(6-8-6)
733
cA2
(6-8-1)
733
cB0
(6-8-3)
733
cC0
(6-8-6)
533B kB0 (6-7-2)NINIXXXXXXXXXXX
533B kC0 (6-7-3)NINIXXXXXXXXXXX
533EB cA2 (6-8-1)XXNIXXXXXXXXXX
600B kC0 (6-7-3)XXXNIXXXXXXXXX
600EB cA2 (6-8-1)XXXXNININIXXXXXX
600EB cB0 (6-8-3)XXXXNININIXXXXXX
600EB cC0 (6-8-6)XXXXNININIXXXXXX
667 cA2 (6-8-1)XXXXXXXNININIXXX
667 cB0 (6-8-3)XXXXXXXNININIXXX
667 cC0 (6-8-6)XXXXXXXNININIXXX
733 cA2 (6-8-1)XXXXXXXXXXNININI
733 cB0 (6-8-3)XXXXXXXXXXNININI
733 cC0 (6-8-6)XXXXXXXXXXNININI
133MHz Slot 1
Pentium III
Stepping
800EB
cA2
(6-8-1)
800EB
cA2
(6-8-1)
800EB
cA2
(6-8-1)
866
cB0
(6-8-3)
866
cC0
(6-8-6)
933
cB0
(6-8-3)
933
cC0
(6-8-6)
1.0B
cB0
(6-8-3)
1.0B
cC0
(6-8-6)
1.13
cC0
(6-8-6)
800EB cA2 (6-8-1)NININIXXXXXXX
800EB cB0 (6-8-3)NININIXXXXXXX
800EB cC0 (6-8-6)NININIXXXXXXX
866 cB0 (6-8-3)XXXNINIXXXXX
866 cC0 (6-8-6)XXXNINIXXXXX
933 cB0 (6-8-3)XXXXXNINIXXX
933 cC0 (6-8-6)XXXXXNINIXXX
1.0B cB0 (6-8-3)XXXXXXXXXX
1.0B cC0 (6-8-6)XXXXXXXXNIX
1.13 cC0 (6-8-6)XXXXXXXXXX

100MHz FC-PGA
Pentium III
Stepping
500
cB0
(6-8-3)
550
cB0
(6-8-3)
600E
cB0
(6-8-3)
600E
cC0
(6-8-6)
600E
cD0
(6-8-A)
650
cB0
(6-8-3)
650
cC0
(6-8-6)
700
cB0
(6-8-3)
700
cC0
(6-8-6)
700
cD0
(6-8-A)
750
cB0
(6-8-3)
750
cC0
(6-8-6)
750
cD0
(6-8-A)
500 cB0 (6-8-3)NIXXXXXXXXXXXX
550 cB0 (6-8-3)XNIXXXXXXXXXXX
600E cB0 (6-8-3)XXNININIXXXXXXXX
600E cC0 (6-8-6)XXNININIXXXXXXXX
600E cD0 (6-8-A)XXNININIXXXXXXXX
650 cB0 (6-8-3)XXXXXNINIXXXXXX
650 cC0 (6-8-6)XXXXXNINIXXXXXX
700 cB0 (6-8-3)XXXXXXXNININIXXX
700 cC0 (6-8-6)XXXXXXXNININIXXX
700 cD0 (6-8-A)XXXXXXXNININIXXX
750 cB0 (6-8-3)XXXXXXXXXXNININI
750 cC0 (6-8-6)XXXXXXXXXXNININI
750 cD0 (6-8-A)XXXXXXXXXXNININI
100MHz FC-PGA
Pentium III
Stepping
800
cB0
(6-8-3)
800
cC0
(6-8-6)
800
cD0
(6-8-A)
850
cB0
(6-8-3)
850
cC0
(6-8-6)
850
cD0
(6-8-A)
900
cC0
(6-8-6)
900
cD0
(6-8-A)
1000
cD0
(6-8-A)
1100
cD0
(6-8-A)
800 cB0 (6-8-3)NININIXXXXXXX
800 cC0 (6-8-6)NININIXXXXXXX
800 cD0 (6-8-A)NININIXXXXXXX
850 cB0 (6-8-3)XXXNININIXXXX
850 cC0 (6-8-6)XXXNININIXXXX
850 cD0 (6-8-A)XXXNININIXXXX
900 cC0 (6-8-6)XXXXXXNINIXX
900 cD0 (6-8-A)XXXXXXNINIXX
1000 cD0 (6-8-A)XXXXXXXXNIX
1100 cD0 (6-8-A)XXXXXXXXXNI

133MHz FC-PGA
Pentium III
Stepping
533EB
cB0
(6-8-3)
600EB
cB0
(6-8-3)
600EB
cC0
(6-8-6)
667
cB0
(6-8-3)
667
cC0
(6-8-6)
733
cB0
(6-8-3)
733
cC0
(6-8-6)
733
cD0
(6-8-A)
800EB
cB0
(6-8-3)
800EB
cC0
(6-8-6)
800EB
cD0
(6-8-A)
533EB cB0 (6-8-3)NIXXXXXXXXXX
600EB cB0 (6-8-3)XNINIXXXXXXXX
600EB cC0 (6-8-6)XNINIXXXXXXXX
667 cB0 (6-8-3)XXXNINIXXXXXX
667 cC0 (6-8-6)XXXNINIXXXXXX
733 cB0 (6-8-3)XXXXXNININIXXX
733 cC0 (6-8-6)XXXXXNININIXXX
733 cD0 (6-8-A)XXXXXNININIXXX
800 cB0 (6-8-3)XXXXXXXXNININI
800 cC0 (6-8-6)XXXXXXXXNININI
800 cD0 (6-8-A)XXXXXXXXNININI
133MHz FC-PGA
Pentium III
Stepping
866
cB0
(6-8-3)
866
cC0
(6-8-6)
866
cD0
(6-8-A)
933
cB0
(6-8-3)
933
cC0
(6-8-6)
933
cD0
(6-8-A)
1.0B
cB0
(6-8-3)
1.0B
cC0
(6-8-6)
1.0B
cD0
(6-8-A)
866 cB0 (6-8-3)NININIXXXXXX
866 cC0 (6-8-6)NININIXXXXXX
866 cD0 (6-8-A)NININIXXXXXX
933 cB0 (6-8-3)XXXNININIXXX
933 cC0 (6-8-6)XXXNININIXXX
933 cD0 (6-8-A)XXXNININIXXX
1.0B cB0 (6-8-3)XXXXXXNININI
1.0B cC0 (6-8-6)XXXXXXNININI
1.0B cD0 (6-8-A)XXXXXXNININI

133MHz
1.25v AGTL
Pentium III
Stepping
866
cD0
(6-8-A)
933
cD0
(6-8-A)
1.0B
cD0
(6-8-A)
1.13
cD0
(6-8-A)
800
tA1
(6-B-1)
1.0B
tA1
(6-B-1)
1.13
tA1
(6-B-1)
1.26
tA1
(6-B-1)
1.4
tA1
(6-B-1)
866 cD0 (6-8-A)NIXXXXXXXX
933 cD0 (6-8-A)XNIXXXXXXX
1.0B cD0 (6-8-A)XXNIXXXXXX
1.13 cD0 (6-8-A)XXXNIXXXXX
800 tA1 (6-B-1)XXXXNIXXXX
1.0B tA1 (6-B-1)XXXXXNIXXX
1.13 tA1 (6-B-1)XXXXXXNIXX
1.26 tA1 (6-B-1)XXXXXXXNIX
1.4 tA1 (6-B-1)XXXXXXXXNI

The cD0 chips listed in the '1.25v AGTL' table immediately above can operate at either 1.5v or 1.25v AGTL+/AGTL in single-chip operation (they are Coppermine-T chips). For DP mode, 1.25v must be used. The tA1 chips are the Tualatin chips (0.13µm, 512KB L2) and can only run at 1.25v AGTL in either single or dual mode operation. All of the other P-III chips listed in the other tables are legacy chips and utilize 1.5v AGTL+ only. Some Coppermine-T and all Tualatin chips come with the large FC-PGA2 heatsink cap. The SL5QE, SL5QF, SL5QJ, and SL5QK chips are Coppermine-T processors, but only QJ and QK come with the new heat spreader. Also note that some regular Coppermine chips also come with the new heat spreader. The new heatsink cap does not automatically mean the chip is Coppermine-T or Tualatin.

Also see: Pentium III Integration Notes.



Intel Xeon

The SL3FK and SL3FR Xeon chips can only be used in a dual configuration; quad isn't possible with these chips. The 133MHz-based Xeon chips can only be used in dual configurations. Chips that run on a 100MHz bus can run in quad and higher configurations.

Taken from the Intel Pentium II Xeon Specification Update PDF File:
100MHz
Pentium II Xeon
Stepping
400
B0
(6-5-2)
400
B1
(6-5-3)
450
B1
(6-5-3)
400 B0 (6-5-2)1,21,2X
400 B1 (6-5-3)1,21X
450 B1 (6-5-3)XX1


Taken from the Intel Pentium III Xeon Specification Update PDF File:
100MHz
Pentium III Xeon
Stepping
500
B0
(6-7-2)
500
C0
(6-7-3)
550
C0
(6-7-3)
700
A0
(6-A-0)
1MB
700
A0
(6-A-0)
2MB
700
A0
(6-A-0')
1MB
700
A0
(6-A-0')
2MB
700
A1
(6-A-1)
1MB
700
A1
(6-A-1)
2MB
700
B0
(6-A-4)
1MB
700
B0
(6-A-4)
2MB
900
B0
(6-A-4)
2MB
500 B0 (6-7-2)NI1,2XXXXXXXXXX
500 C0 (6-7-3)1,2NIXXXXXXXXXX
550 C0 (6-7-3)XXNIXXXXXXXXX
700 A0 (6-A-0) 1MBXXX3XXX1X1,4XX
700 A0 (6-A-0) 2MBXXXX3XXX1X1,4X
700 A0 (6-A-0') 1MBXXXXX3XXXXXX
700 A0 (6-A-0') 2MBXXXXXX3XXXXX
700 A1 (6-A-1) 1MBXXX1XXXNIX1,4XX
700 A1 (6-A-1) 2MBXXXX1XXXNIX1,4X
700 B0 (6-A-4) 1MBXXX1,4XXX1,4X4XX
700 B0 (6-A-4) 2MBXXXX1,4XXX1,4X4X
900 B0 (6-A-4) 2MBXXXXXXXXXXX4

133MHz
Pentium III Xeon
Stepping
600
cA2
(6-8-1)
667
cA2
(6-8-1)
733
cA2
(6-8-1)
800
cA2
(6-8-1)
600
cB0
(6-8-3)
667
cB0
(6-8-3)
733
cB0
(6-8-3)
733
cC0
(6-8-6)
800
cB0
(6-8-3)
800
cC0
(6-8-6)
866
cB0
(6-8-3)
866
cC0
(6-8-6)
933
cC0
(6-8-6)
1000
cC0
(6-8-6)
600 cA2 (6-8-1)NIXXX1XXXXXXXXX
667 cA2 (6-8-1)XNIXXX1XXXXXXXX
733 cA2 (6-8-1)XXNIXXX11XXXXXX
800 cA2 (6-8-1)XXXNIXXXX11XXXX
600 cB0 (6-8-3)1XXXNIXXXXXXXXX
667 cB0 (6-8-3)X1XXXNIXXXXXXXX
733 cB0 (6-8-3)XX1XXXNI1XXXXXX
733 cC0 (6-8-6)XX1XXX1NIXXXXXX
800 cB0 (6-8-3)XXX1XXXXNI1XXXX
800 cC0 (6-8-6)XXX1XXXX1NIXXXX
866 cB0 (6-8-3)XXXXXXXXXXNI1XX
866 cC0 (6-8-6)XXXXXXXXXX1NIXX
933 cC0 (6-8-6)XXXXXXXXXXXXNIX
1000 cC0 (6-8-6)XXXXXXXXXXXXXNI


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