The 80386 processor may operate in conjunction with, and utilize the features of either the Intel 80287 or 80387 numeric coprocessors. When the system is initialized, the presence of a numeric coprocessor, and its type if present, is checked by the 80386. If an 80287 coprocessor is detected, the 80386 automatically converts all memory transfers to 16-bit format. If an 80387 is detected, it is used in 32-bit mode, thereby utilizing the full potential of both the 80386 and 80387.
Note: IBM does not support or recommend the use of 80287 numeric coprocessors in 80386-based systems. For a list of supported numeric coprocessors for each system unit, readers should refer to the appropriate IBM Product Announcement for that system unit.