Abstract: A method and apparatus for subdividing a thread's processing cycles among a set of threadlets or regions within a thread or process. This is achieved through instructions in the application code which are interpreted by the operating system. The beginning and ending of a threadlet is through the "Begin Threadlet" and "End Threadlet" instructions. A segmented stack is utilized to separately hold that part of the stack belonging to each threadlet. The programmer must know within the application code places where the data contents of the registers do not merit saving or is saved in memory. This provides the user with an opportunity to switch to a different activity without saving registers. The user identifies this to the operating system by a special instruction called "SWITCHIR". The SWITCHIR instruction tells the operating system not to save registers. Therefore, within the same thread, the operating system will keep on executing a threadlet until it encounters this instruction.