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Week 06 top 10 list of interesting OS things

1. Role of Interrupts
   As the name suggests, interrupt signals provide a way to divert the processor to code outside the normal flow of control. When an interrupt signal arrives, the CPU must stop what it’s currently doing and switch to a new activity; it does this by saving the current value of the program counter (i.e., the content of the eip and cs registers) in the Kernel Mode stack and by placing an address related to the interrupt type into the program counter.

2. I/O scheduling
   Operating System has a certain portion of code that is dedicated to managing Input/Output in order to improve the reliability and the performance of the system. A computer system contains CPUs and more than one device controllers connected to a common bus channel, generally referred to as the device driver. These device drivers provide an interface to I/O devices for communicating with the system hardware promoting ease of communication providing access to shared memory.

3. Context Switching
   Context Switching involves storing the context or state of a process so that it can be reloaded when required and execution can be resumed from the same point as earlier. This is a feature of a multitasking operating system and allows a single CPU to be shared by multiple processes.

4. Kernel vs User Thread
   A thread is a lightweight process that can be managed independently by a scheduler. It improves the application performance using parallelism. A thread shares information like data segment, code segment files etc. with its peer threads while it contains its own registers, stack, counter etc.

5. Memory-mapped IO vs Port-mapped IO
   Microprocessors normally use two methods to connect external devices: memory mapped or port mapped I/O. However, as far as the peripheral is concerned, both methods are really identical. Memory mapped I/O is mapped into the same address space as program memory and/or user memory, and is accessed in the same way. Port mapped I/O uses a separate, dedicated address space and is accessed via a dedicated set of microprocessor instructions.

6. Difference between Concurrency and Parallelism
   Concurrency relates to an application that is making progress more than one task at the same time. Concurrency is a approach that is used for decreasing the response time of the system by using the single processing unit. On the other hand, Parallelism related to an application in which the tasks are divided into smaller sub-tasks that are processed simultaneously or parallel. It is used for increasing the throughput and computational speed of the system by using the multiple processors. It is the technique that do lot of things simultaneously.

7. Single vs Multithreaded Process
   This page goes into full detail about the inctricacies of single vs multithreaded process with opinions from people who can be trusted ont his subject.

8. Client server system
   The client-server model, or client-server architecture, is a distributed application framework dividing tasks between servers and clients, which either reside in the same system or communicate through a computer network or the Internet. The client relies on sending a request to another program in order to access a service made available by a server. The server runs one or more programs that share resources with and distribute work among clients.

9. Shared Memory vs Message Passing
   Message passing model allows multiple processes to read and write data to the message queue without being connected to each other. Messages are stored on the queue until their recipient retrieves them. Message queues are quite useful for interprocess communication and are used by most operating systems. The shared memory in the shared memory model is the memory that can be simultaneously accessed by multiple processes. This is done so that the processes can communicate with each other. All POSIX systems, as well as Windows operating systems use shared memory.

10. Cooperating Processes
    n the computer system, there are many processes which may be either independent processes or cooperating processes that run in the operating system. A process is said to be independent when it cannot affect or be affected by any other processes that are running the system. It is clear that any process which does not share any data (temporary or persistent) with any another process then the process independent. On the other hand, a cooperating process is one which can affect or affected by any another process that is running on the computer. the cooperating process is one which shares data with another process.