When verifying if processors will work in your dual processing system, you must first determine if the processors will support dual processing, and if the processors will work with each other. Therefore, you must check the following:

1. The processors must be dual processing capable. Dual processing capable processors include:
   • Pentium® III processors
   • Pentium® II processors
   • Pentium® III Xeon® processors
   • Pentium® II Xeon® processors
   • Intel® Xeon® processor
   • Dual-Core Intel® Xeon® processors 5000 sequence 

   Note: Pentium III processors based with 256 KB cache and using .13µ process technology do not support dual processor. Pentium III processors with 512 KB cache and using .13µ process technology do support dual processing.
   
   Determining if the processor supports dual processing can also be done by referencing the processor's Specification Update Guide. Find your sSpec number in the Specification Update Guide under the Processor Identification and Package Information tables, and read the notes for your particular processor to determine if it is dual processing capable. An sSpec is the five digit number that starts with an 'S' and is followed by 4 characters (for example, 'SL3CC').

   By looking up the sSpec number in the Specification Update Guide, you can find the core stepping, speed, bus speed, cache size, package type and notes for the processor. See Figure 1 below.

2. The processors must have identical frequency, bus speed and cache size. In addition, when viewing the Specification Update Guide, notice that each sSpec has a CPUID string, which is four characters in length. The first character is typically a 0, the second character represents the family number, and third character represents the model number. The fourth character represents the processor's core stepping. A stepping is a minor change in the processor. Processors used in a dual processing system must share the same family and model number. This will ensure that processors used in a dual processing system will have the same speed, same cache size and same bus speed. For example, if you find one processor with a CPUID of 0672 and a second processor with a CPUID of 0673, both processors have the same family and model number of 67. In many cases, you may mix processor steppings in a dual processor system.

3. The processors must have compatible steppings. By using the Specification Update Guide, you can find the processor's stepping by referring to the Processor Identification and Package Information tables. Then you need to cross-reference both steppings, processor speeds and bus speeds with the DP Platform Population Matrix table(See Figure 2) to see if there are any issues with the match. NI indicates no issues.

   Note: Identical silicon steppings may sometimes be shipped with different sSpec numbers, depending on whether they are for OEMs (tray processors) or for system integrators (boxed processors).

The DP Platform Matrix used in the Specification Update Guides can determine if steppings are compatible. In the example above, Pentium III processors running at 600 MHz with a 133 MHz bus and 256 KB cache have no issues between processors using the cB0 stepping and the cC0 stepping. Even though Intel recommends using identical processor steppings in dual processor systems whenever possible (as this is the only configuration which receives Intel's full testing), Intel does support mixing processor steppings, and does not actively prevent various steppings of the Pentium III processor from working together in dual-processor systems. However, since Intel cannot test every possible combination of devices, each new stepping of a device is fully tested only against the latest steppings of other processors and chipset components. In addition, when partially populated systems are shipped, a customer returning for additional processors may have difficulty locating a processor with a compatible stepping. If this occurs, the customer may have to replace the original processor to obtain a system with two processors of the same stepping.

This applies to:

Intel® Pentium® II Processor Intel® Pentium® II Xeon® Processor Intel® Pentium® III Processor Intel® Pentium® III Xeon® Processor Intel® Xeon® Processor Multi-Core Intel® Xeon® Processor 5000 Sequence