This chip is Intel's second-generation 287, first introduced in 1990. Since it is based on the 80387 coprocessor core, it features full IEEE 754 compatibility and faster instruction execution. Intel claims about 50% faster operation than the 80287 for typical benchmark tests. Compared with benchmark results for the AMD 80C287, which is identical to the Intel 80287, the Intel 287XL performed 66% faster than the AMD 80C287 on a fractal benchmark and 66% faster on the Whetstone benchmark.
Since the 287XL has all the additional instructions and enhancements of a 387, most software automatically identifies it as an 80387-compatible coprocessor and therefore can make use of extra 387-only features, such as the FSIN and FCOS instructions.
The 287XL is manufactured in CMOS and therefore uses much less power than the older NMOS-based 80287. At 12.5 MHz, the power consumption is rated at max. 675 mW, about 1/4 of the 80287 power consumption. The 287XL is available in either a 40-pin CERDIP (ceramic dual inline package) or a 44 pin PLCC (plastic leaded chip carrier). (This latter version is called the 287XLT and intended mainly for laptop use.) The 287XL is rated for speeds of up to 12.5 MHz.
Comment by Paul Collins (pi314aussie[at]yahoo.com): Our shop sold these in big cardboard boxes. They were 20MHz chips, sold as covering all speed m/boards out there from 6MHz to 20MHz. See my note for D80287-10......my own personal 286-20 m/board run a fixed 10MHz clock for the FPU co-pro socket, so where were these m/boards that needed a true 20MHz chip??? My m/board was made in 1993! (After the release of the XL-20 FPU's).