3.5. Mixing Processors

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The Intel processor line includes several families of processors with varying core frequencies, L2 cache sizes, and steppings. Customer desire for investment protection and their growing need to scale processing power and to redeploy server components make the ability to mix processors in dual-processor and multiprocessor systems a significant customer benefit.

To ensure full protection and support under manufacturer warranties, users must configure computer hardware and software according to manufacturer guidelines. In the case of processors for use in servers, guidelines of multiple vendors must be reconciled: those of the processor manufacturer, the server manufacturer, and the operating system vendor. The question of vendor support for Intel processor mixing is clouded by differences in vendor testing programs and vague wording of vendor support policies.

! Important

Four-way platforms, starting with the Intel Xeon processors, no longer support processor mixing.


With the rapid introduction of new processors and the race to bring new products to market, no vendor has sufficient time and resources to test every possible combination of mixed processors for all potential problems. Intel conducts its own testing program for the processors it markets and publishes identified errata and workarounds on the Intel website.

For compatibility testing through its Windows Hardware Quality Labs and certification through the Microsoft Windows Logo Program for hardware, Microsoft Corporation requires that systems meet defined processor configuration restrictions.

Other operating system vendors might have their own qualification procedures for multiprocessor servers. HP, other manufacturers, and users are free to do additional validation of mixed processor configurations if they choose.

3.5.1 Processor Steppings

Processor steppings are versions of the same processor model (for example, the Intel Pentium III Xeon processor) that vary only slightly, usually to improve performance or manufacturing yield. Each stepping requires changes to the system ROM. For each processor stepping that it produces, Intel provides a microcode patch for inclusion in the system ROM.

Each Intel processor stepping has a unique processor ID, and its microcode patch contains the same processor ID. The microcode patches are stored in a table within the system ROM. HP and other server vendors must continually add newly released Intel patches to keep their ROMs current.

After a processor has been installed, stepping identification can be problematic because a heat sink typically covers the top of the processor chip. Utilities provided with operating systems might help. For example, under Windows NT, a system administrator can use the Windows NT Diagnostics utility to identify the stepping level of each installed processor. Alternatively, a system administrator can use the Survey utility to view the steppings of installed processors.

3.5.2 Intel Support for Processor Mixing

Based on the information available on the Intel Web site at the time of this writing, Intel supports mixed steppings of processors only if all processors in a system meet the following criteria:

  • Have identical family and model numbers as indicated by the CPU ID instruction.

  • Operate at the same frequency that is, at the highest frequency rating commonly supported by all the processors.

  • Have the same cache size.

  • The processor with the lowest feature set must be the bootstrap processor.

Note

The bootstrap processor is the primary processor in a multiprocessor system. It is the main processor that starts the system and from which it loads the operating system and performs most functions. The remaining processors in a multiprocessor system are application processors.


3.5.3 Operating System Support for Processor Mixing

Like Intel, operating system vendors support the mixing of processors only if all processors in a system meet the following criteria:

  • Have identical family and model numbers.

  • Operate at the same frequency.

  • Have the same cache size.

  • The processor with the lowest feature set must be the bootstrap processor.

Statements from operating system vendors tend to be vague about support for mixed processor steppings. The most common operating systems typically do not inhibit the operation of servers containing multiple processors with different steppings.

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    HP ProLiant Servers AIS. Official Study Guide and Desk Reference
    HP ProLiant Servers AIS: Official Study Guide and Desk Reference
    ISBN: 0131467174
    EAN: 2147483647
    Year: 2004
    Pages: 278

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