In OS/360, IBM extended the overlay facility of IBLDR by allowing an overlay program to have independent overlay regions, each with its own overlay tree.
ɪn ˌoʊˈɛs slˈæʃ θɹˈiːhˈʌndɹɪd sˈɪksti, ˌaɪbˌiːˈɛm ɛkstˈɛndᵻd ðɪ ˌoʊvɚlˈeɪ fəsˈɪlᵻɾi ʌv ˈɪbldɚ baɪ ɐlˈaʊɪŋ ɐn ˌoʊvɚlˈeɪ pɹˈoʊɡɹæm tə hæv ˌɪndᵻpˈɛndənt ˌoʊvɚlˈeɪ ɹˈiːdʒənz, ˈiːtʃ wɪð ɪts ˈoʊn ˌoʊvɚlˈeɪ tɹˈiː.