What type of multitasking did older OSs use, which allowed a process to monopolize the CPU's time until the process had completed its own task

Acontact list is a place where you can store a specific contact with other associated information such as a phone number, email address, birthday, etc. write a program that first takes in word pairs that consist of a name and a phone number (both strings). that list is followed by a name, and your program should output that name's phone number.