The stability of sorting method: if there are two objects r and rlil in the object series, and their sorting codes are k==klil,And before sorting, object rli is in front of object r[ji. If after the sorting, objectrlil is still in front of object rIil, then we call this sorting method stable, otherwise we call this sorting method unstable. Inner sort and outer sort: inner sort means in the sorting period, all the data objects are in the memory. Outer sort means in the sorting period, since the number of object is too large, and they cannot be put in the memory at the same time. We must move the sorting between inner and outer memory according to the demand.◼ The stability of sorting method: if there are two objects r[i] and r[j] in the object series, and their sorting codes are k[i] == k[j],And before sorting, object r[i] is in front of object r[j] .If after the sorting, object r[i] is still in front of object r[j] , then we call this sorting method stable, otherwise we call this sorting method unstable. ◼ Inner sort and outer sort: inner sort means in the sorting period, all the data objects are in the memory. Outer sort means in the sorting period, since the number of object is too large, and they cannot be put in the memory at the same time. We must move the sorting between inner and outer memory according to the demand