in Layered Approach Each layer uses the functions of only the lower-level layers.

means that if a process terminates, all of its children must be terminated as well

Reasons to support process cooperation

A RPC on the client-side hides the communication details

Threads can run in parallel on a multiprocessor machine.

traditional process has a multiple thread of control.

Identifying tasks is divide program into tasks that can run in series

a ....... system has well defined, fixed time constraints

Task Parallelism refers to the distribution of data across multiple cores

User threads are managed with OS support

Kernel threads are supported and managed directly by the OS.

in One-to-One Model Only one user thread can access the kernel at a time.

in Many-to-One Model Threads can run in parallel on multi-core systems.

in One-to-One Model Multiple threads can access the kernel at a given time

OS creates a kernel thread per user thread (can burden performance)

OS creates a set of kernel threads (less than or equal to user threads)

When a thread makes a blocking system call, another thread can run.

Most operating systems use

Fork-join. works well for tasks that are asynchronous (cooperating)