Without virtual memory, what were programmers typically required to use?

Prior to the introduction of virtual memory, programmers often had to use overlays to manage memory effectively. Overlays allowed the loading of only essential parts of a program into memory at any given time, which was crucial because the limited memory on older systems could only accommodate a portion of larger applications. This technique involved dividing a program into smaller segments, where portions could be loaded and unloaded as needed to execute the program without exceeding the available physical memory.

Using overlays enabled programmers to work around the constraints of limited RAM while still allowing for the execution of complex applications. Each overlay would contain a part of the application's functionality, and the system would switch between them as required, ensuring that the active code and data were always in memory while the rest remained on disk until needed. This approach was essential for efficient memory management before virtual memory systems became commonplace, allowing for more seamless multitasking and larger program capabilities.