CS & BCA Notes

  Operating System Unit I Process Management Introduction to Process: A program in execution is called a process. The execution of a process must progress in a sequential fashion. In order to complete its task, process needs the computer resources. A process can be defined as an entity which represents the basic unit of work to be implemented in the system. The operating system has to manage all the processes which require the same resource at the same time , in a convenient and efficient way. The Process Management Involves, Scheduling processes and threads on the CPUs. Creating and deleting both user and system processes. Suspending and resuming processes. Providing mechanisms for process synchronization. Providing mechanisms for process communication. Process Architecture A program becomes a process, when it is loaded into the memory. A process in memory can be divided in 4 sections

Operating System Architecture    1.        MONOLITHIC SYSTEMS     The core software components of an operating system are collectively known as the kernel . The kernel has unrestricted access to all of the resources on the system.  In monolithic systems , each component of the operating system was contained within the kernel, could communicate directly with any other component, and had unrestricted system access. While  this made the  operating system very efficient, it also meant that errors were more difficult to isolate, and there was a high risk of damage due to erroneous or malicious code.  2.  L ayered OS architecture   The layered structure approach breaks up the operating system into different layers and retains much more control on the system.         The bottom layer (layer 0) is the hardware, and the topmost layer (layer N) is the user interface. These layers are so designed that each layer uses the functions of the lower-level layers only.   It simplifies the debugging