The Intel Pentium processors have a wide variety of built-in facilities for supporting multiprocessing, including hardware cache coherency, built in interprocessor interrupt handling and a set of atomic test and set, exchange and similar operations. The cache coherency in particular makes the operating systems job far easier.
The specification defines a detailed configuration structure in ROM that the boot up processor can read to find the full configuration of the processors and busses. It also defines a procedure for starting up the other processors.