sentences:  Program modules were written to allow different modules to share the same memory region and the main program itself was responsible of exchanging modules between disk and memory as necessary.In the mid-to-late 1960s, mainframe computers, such as the IBM System/360, had memory sizes from 8 KB to 512 KB.In order to conserve memory, transients were small modules that supported a specific task, and were swapped in and out of memory.