are multithreading, multiprocessing, multitasking implemented at instruction set or OS?

On a computer with a single cpu core,

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  must a multithreading program be implemented based on an OS? Can it be implemented in the instruction set and run without an OS?

  
  


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  Can multiple programs run in multitasking way without an OS? Can multitasking between programs be implemented without an OS (e.g. implemented only in the instruction set)?

  
  

On a computer with multiple cpus/cores,

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  must a multithreading program be implemented based on an OS? Can it be implemented in the instruction set and run with parallel threads without an OS?

  
  


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  Can multiple processes run in multiproccessing parallel way without an OS? Can this multiproccessing parallelism be implemented without an OS (e.g. but in the instruction set)?

  
  

The motivation of my questions is:

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  Are multithreading, multiprocessing,and multitasking, respectively, intrinsic to computer architecture or to operating system? (note: an OS is implemented based and runs on a computer architecture. Concepts intrinsic to a computer architecture can be independent of OS)

  
  


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  Some parallelisms such as pipeline, superscalar, and vector computing are intrinsic to computer architecture , and independent of OS. Are thread and process level parallelisms intrinsic to computer architecture, or to OS? Is multitasking ( as a kind of concurrent computing) intrinsic to computer architecture or OS?

  
  

Thanks.