1. In dual processor systems, the processor with the lowest feature-set, as determined by the CPUID Feature Bytes, must be the Bootstrap Processor (BSP). The BSP is the processor that starts the boot process. In the event of a tie in feature-set, the tie should be resolved by selecting the BSP as the processor with the lowest stepping as determined by the CPUID instruction. For example, when mixing b0 and c0 the b0 stepping is the lowest.
   
   
2. Be sure to use an operating system that supports dual processing. Currently, Microsoft* Windows NT*, Windows 2000, Windows XP* Professional and some versions of Linux support dual processing. Microsoft Windows 95, Windows 98, Windows Me and Windows XP Home do not. If you only have one processor installed when you install Windows NT or Windows 2000, you will need to change the HAL to a dual processing HAL when you start using more than one processor. For Linux to support multiple processors, you may have to recompile the kernel. Check with the documentation that comes with the OS.
   
   Note: for the software to make use of dual processing, the software has to be multi-threaded and it must be running on an operating system that supports dual processing.
   
   
3. If you use a dual processing motherboard and you don't use all of the processors, some motherboards require having a special terminator card in the empty processor slot(s). If the motherboard is self-terminating and you are having problems booting, you may try inserting a special terminator or a matched processor in the empty slot or socket to verify that the self-termination is actually working properly.
   
   
4. Check the BIOS Settings. Some boards may have options to retest or enable/disable processors.

This applies to:

Intel® Celeron® Processor Family Intel® Pentium® 4 Processor Extreme Edition Intel® Pentium® 4 Processors Intel® Pentium® II Processor Intel® Pentium® II Xeon® Processor Intel® Pentium® III Processor Intel® Pentium® III Xeon® Processor Intel® Pentium® M Processor Intel® Pentium® Pro Processors Intel® Pentium® Processor Intel® Pentium® Processor with MMX™ Technology Intel® Xeon® Processor Mobile Intel® Celeron® Processors Mobile Intel® Pentium® 4 Processors - M Mobile Intel® Pentium® II Processors Mobile Intel® Pentium® III Processor Mobile Intel® Pentium® Processors OverDrive® Processors