base address 基址：
the part of a two-part memory address that remains constant and provides a reference point from which the location of a byte of data can be calculated. a base address is accompanied by an offset value that is added to the base to determine the exact location(the absolute address)of the information. the concept is similar to a street address system . for example, "2010 main street " plus an offset(10from the beginning of the block ).base address are known as segment address in IBM pcs and compatibles; data in these computers is identified by its position as a relative offset the start of the segment.