Programming an 8259 in conjunction with DOS and Microsoft Windows has introduced a number of confusing issues for the sake of backwards compatibility, which extends as far back as the original PC introduced in 1981.
MS-DOSやMicrosoft Windowsで8259を使う際には、後方互換性、つまり1981年に採用された初代PCと互換性を残しつつ拡張してきたため、多くの面倒な問題が持ち込まれる。