PDF of 119 KB named 27C256B, filed as a schematic yet clearly a part number from the 27C CMOS EPROM line, here with a B revision letter.

Datasheet in a 106 KB PDF for the 27c256, a part number in the common 27C CMOS EPROM family, although the catalogue lists it as a schematic.

Very short 20.1 KB PDF for the part 27C256-12A, catalogued as a schematic. The number belongs to the 27C EPROM family, and the -12 suffix normally reflects the…