Operating Systems: Processes and IPC

• Operating Systems (OS) primarily manage hardware and offer a user interface.
• The Kernel is the core of the OS, responsible for managing hardware and critical functions.
• The main OS operation modes include User Mode and Kernel Mode.

Multiprogramming and Time-Sharing

• Multiprogramming involves loading multiple programs into memory to make better use of the CPU.
• Time-sharing in OS involves allocating CPU time among multiple users simultaneously.

Processes

• A process is a program in execution.
• A process consists of code, data, and execution context.
• The Process Control Block (PCB) contains information to manage a process.
• The dispatcher switches the CPU from one process to another.

Inter-Process Communication (IPC)

• Inter-Process Communication (IPC) provides a mechanism for processes to communicate and synchronize.
• An optical bus is NOT a valid IPC model.
• Shared memory IPC communicates by accessing a common memory space.
• The main operations in message passing IPC are send() and receive().
• Direct communication in IPC relies on processes naming each other explicitly.
• A mailbox in IPC serves as a shared buffer for exchanging messages.
• Blocking communication occurs when the sender/receiver waits until the other party is ready.
• Non-blocking communication allows the sender/receiver to continue without waiting.
• A rendezvous in IPC is a sync where both the sender and receiver block.

Real-Time Systems

• A real-time system operates with timing constraints and must maintain logical correctness.
• A hard real-time system dictates that missing a deadline is unacceptable.
• A soft real-time system tolerates missed deadlines but experiences degraded value.
• A firm real-time system has zero value if completed after the deadline, but it's not harmful.

Deadlocks and Synchronization

• Deadlocks in OS occur when processes wait on each other indefinitely.
• Improper synchronization stems from poorly designed signaling between processes.
• Failed mutual exclusion occurs when more than one process accesses a shared resource simultaneously.

Virtual Memory

• Virtual memory is a memory abstraction that allows programs to run beyond physical memory limits.
• Paging in virtual memory divides memory into fixed-size pages.
• Process isolation protects processes from interfering with each other's memory.
• Memory protection restricts access to sensitive memory regions.

Scheduling

• Scheduling in OS involves deciding which process should run next.
• Scheduling policies aim for fairness, responsiveness, and efficiency.
• A context switch involves saving and restoring the process state during switching.
• A trace of a process shows the sequence of executed instructions.
• Preemptive scheduling uses timer interrupts to control processes.
• Non-preemptive scheduling relies on tasks voluntarily yielding control.
• During a context switch, the OS saves the old process state and loads the new one.

Modularity and Memory

• Modular programming support is when code is divided into reusable, independent modules.
• Automatic memory allocation is when the OS automatically assigns memory to processes.
• Access control in an OS prevents unauthorized access to system resources.
• In batch systems, the monitor manages job sequencing and execution.
• The overhead in simple batch systems includes CPU and memory usage by the monitor.

System Improvements and Errors

• Time-sharing improves system responsiveness and CPU utilization.
• The main causes of OS-level errors include deadlocks, improper synchronization, and failed mutual exclusion.
• A scheduler chooses the next process to run.
• The Five-State Process Model describes process states: New, Ready, Running, Blocked, Exit.
• Process suspension is used for freeing main memory by moving processes to disk.
• When all processes are blocked, processes may be suspended to free resources.
• A processors trace shows the sequence of dispatched processes and switches.
• Multiple blocked queues facilitates the grouping of blocked processes by event type for efficient management.