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The operating system has two primary purposes: (1) to protect the hardware from misuse by runaway applications and (2) to provide applications with simple and uniform mechanisms for manipulating complicated and often wildly different low-level hardware devices.
Shell is the outermost layer of the Operating System and handles user interaction. It interprets input for the OS and handles the output from the OS.
The kernel is the core component of the operating system. The kernel is the primary interface between the Operating system and Hardware.
Process Schedulers are fundamental components of operating systems responsible for deciding the order in which processes are executed by the CPU. Include:
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Long-Term Scheduler(Job Scheduler)
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Short-Term Scheduler(CPU Scheduler)
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Medium-Term Scheduler
Comparison Among Scheduler:
| Long-Term Scheduler | Short-Term Scheduler | Medium-Term Scheduler |
|---|---|---|
| It is a job scheduler | It is a CPU scheduler | It is a process-swapping scheduler |
| It is the slowest scheduler | It is the fastest scheduler | It's speed lies between long-term and short-term schedulers |
| It controls the degree of multiprogramming | It gives less control over the degree of multiprogramming | It reduces the degree of multiprogramming |
| It is barely present or nonexistent in time-sharing systems | It is essential for time-sharing systems | It is a component of time-sharing systems |
| It selects processes from the job poll and loads them into memory | It selects ready processes for execution by the CPU | It can re-introduce processes into memory and resume execution |
| Process | Thread | Coroutine | |
|---|---|---|---|
| Scheduling | Runs independently. | Basic unit of scheduling and dispatch; actually runs on CPU. | Fully controlled by user. |
| Resources | Has independent resources. | All threads in a process share resources; more efficient. | Has its own register context and stack. |
| Overhead | Large overhead for creation/destruction and context switch. | Small overhead. | Can save/restore state; switching has almost no overhead. |
| Concurrency | Processes run independently. | Preemptive multitasking; threads need locks; less robust. | Cooperative multitasking; no locks needed; more robust. |
| Thread Context Switch | Process Context Switch |
|---|---|
| TCS occurs when the CPU saves the current state of the thread and switches to another thread of the same process. | PCS occurs when the operating system's scheduler saves the current state of the running Program (including the state of the PCB) and switches to another program. |
| TCS helps the CPU to handle multiple threads simultaneously. | PCS involves loading of the states of the new program for it's execution. |
| TCS does not involve switching of memory address spaces. All the memory addresses that the processor accounts for remain saved. | PCS involves switching of memory address spaces. All the memory addresses that the processor accounts for get flushed. |
| The processor's cache and Translation Lookaside Buffer preserve their state. | The processor's cache and TLB get flushed. |
| Though TCS involves switching of registers and stack pointers, it does not incur the cost of changing the address space. Hence, it is more efficient. | PCS involves the high cost of changing the address space. Hence, it is less efficient. |
| TCS is a bit faster and cheaper. | PCS is relatively slower and costlier |
| Zombie Process | Orphan Process | Daemon Process |
|---|---|---|
| A zombie is a process that has completed its task but still shows an entry in a process table. | An orphan process is a computer process that continues even after its parent terminates. The init process becomes its parent and continues the remaining task. | A daemon process is a system-related process that always runs in the background. |
| Zombie process states are always indicated by "Z" | An orphan process is often created unintentionally due to a system crash. | A daemon process state indicated by '?' in the TTY column in the output |
| A zombie process does not have controlling terminals | An Orphan process has controlling terminals. | A daemon process does not have controlling terminals. |
| A zombie process is treated as dead and is not used for system processing. | An orphan process is a computer process that, even after its parent terminates, init is become a parent and continues the remaining task. | A program that runs for a long time makes them as a daemon process and runs it in the background. |
| To remove the zombie process, execute the kill command. | To terminate the Orphan process, use the SIGHUP signal. | A daemon process terminates only when the system shuts down. |
OS Dispather
OS Scheduler
| Scheduler | Dispatcher |
|---|---|
| Decides which process should be executed next. | Transfers control of CPU to the process selected by the scheduler. |
| To select the process and determine execution order. | To start the execution of the selected process. |
| Long-term, Medium-term and Short-term. | No types; it's a single module. |
| Works independently. | Dependent on the scheduler's decision. |
| Uses algorithms like FCFS, SJF, RR, Priority, etc. | No specific algorithm used. |
| Negligible and occurs less frequently. | Time taken is known as Dispatch Latency. |
| Process selection and queue management. | Context switching, mode change and process start. |
| Works with the ready queue and dispatcher. | Works with CPU and the selected process. |
| Takes longer than the dispatcher. | Executes in a very short time. |
| Multiprogramming | Multi-tasking |
|---|---|
| Involves loading multiple programs into the computer's memory and allowing them to share the CPU. The CPU switches between programs, especially when one is waiting for I/O operations to complete. | Refers to the ability of an operating system to execute multiple tasks (or processes) simultaneously by rapidly switching between them. |
| The main goal is to increase CPU utilization by reducing idle time. | The primary goal is to improve user responsiveness and allow for interactive computing |
| It does not involve direct user interaction. | Designed with user interaction, allowing users to run multiple applications (e.g., word processors, web browsers, etc.) simultaneously |
| Less complex than multitasking. It focuses on keeping the CPU busy by running one program at a time until it needs to wait for an I/O operation. | More complex one. It requires more sophisticated scheduling algorithms and resource management to handle multiple tasks, user inputs, and ensure a smooth experience. |
| There will be no effect of Parallelism. | It will give rise to the concept of Parallelism |
| Used in environments where resource utilization is more critical, such as batch processing, and where tasks are long-running. | Used in interactive environments where multiple applications need to be run concurrently, particularly in desktop and mobile operating systems. |
| Multi-tasking | Multiprocessing |
|---|---|
| The execution of more than one task simultaneously is known as multitasking. | The availability of more than one processor per system, which can execute several sets of instructions in parallel, is known as multiprocessing. |
| The number of CPUs is one. | The number of CPUs is more than one. |
| It takes a moderate amount of time. | It takes less time for job processing. |
| In this, one by one job is being executed at a time. | In this, more than one process can be executed at a time. |
| It is economical. | It is less economical. |
| The number of users is more than one. | The number of users is can be one or more than one. |
| Throughput is moderate. | Throughput is maximum. |
| Its efficiency is moderate. | Its efficiency is maximum. |
| It is of two types: single-user multitasking and multiple-user multitasking. | It is of two types: Symmetric Multiprocessing and Asymmetric Multiprocessing. |
| Linux | Unix |
|---|---|
| The source code of Linux is freely available to its users | The source code of Unix is not freely available to the general public |
| It has a graphical user interface along with a command line interface | It only has a command line interface |
| Linux OS is portable, flexible, and can be executed on different hard drives | Unix OS is not portable |
| Different versions of Linux OS are Ubuntu, Linux Mint, RedHat Enterprise Linux, etc. | Different versions of Unix are AIS, HP-UX, BSD, Iris, Solaris, etc. |
| The file systems supported by Linux are as follows: xfs, ramfs, vfat, cramfsm, ext3, ext4, ext2, ext1, ufs, autofs, devpts, ntfs | The file systems supported by Unix are as follows: zfs, js, hfx, gps, xfs, vxfs |
| Linux is an open-source operating system that was first released in 1991 by Linus Torvalds. | Unix is a proprietary operating system that was originally developed by AT&T Bell Labs in the mid 1960s. |
| The Linux kernel is monolithic, meaning that all of its services are provided by a single kernel. | The Unix kernel is modular, meaning that it is made up of a collection of independent modules that can be loaded and unloaded dynamically. |
| Linux has much broader hardware support than Unix. | Unix was originally designed to run on large, expensive mainframe computers, while Linux was designed to run on commodity hardware like PCs and servers. |
| The user interface of Linux is Graphical or text-based. | The user interface of Unix is text-based. |
| Command Line Interfaces of Linux are Bash, Zsh, and Tcsh. | Command Line Interface of Unix is Bourne, Korn, C, and Zsh. |
[1] Randal E. Bryant, David R. O'Hallaron . COMPUTER SYSTEMS: A PROGRAMMER'S PERSPECTIVE . 3ED
[3] Introduction to Operating System
[4] Types of Operating Systems
[5] Kernel in Operating System
[6] System Call
[7] Process Schedulers in Operating System