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Overview: Operating Systems for Computer Hardware Resources

An operating system (OS) manages computer hardware and software resources and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources.
The dominant general-purpose personal computer operating system is Microsoft Windows with a market share of around 74.99%. macOS by Apple Inc. is in second place (14.84%), and the varieties of Linux are collectively in third place (2.81%).
Android's share is 70.82% in the mobile sector (including smartphones and tablets) in 2020.
Linux distributions are dominant in the server and supercomputing sectors.
Single-tasking systems can only run one program at a time, while multi-tasking operating systems allow more than one program to run concurrently.
Single-user operating systems have no facilities to distinguish users but may allow multiple programs to run in tandem. Multi-user operating systems extend the basic concept of multi-tasking with facilities that identify processes and resources belonging to multiple users.
A distributed operating system manages a group of distinct, networked computers and makes them appear to be a single computer.
Embedded operating systems are designed to be used in embedded computer systems and operate on small machines with less autonomy.
A real-time operating system guarantees to process events or data by a specific moment in time.
A library operating system provides services that a typical operating system provides in the form of libraries and composed with the application and configuration code to construct a unikernel.
Early computers were built to perform a series of single tasks, and operating systems did not exist in their modern and more complex forms until the early 1960s.Overview of Operating Systems
Unix was originally written in assembly language and developed into a family of inter-related operating systems that have been influential in every modern operating system.
The Unix-like family is a diverse group of operating systems, including System V, BSD, and Linux.
The BSD family includes FreeBSD, NetBSD, and OpenBSD, which were developed at the University of California, Berkeley, and widely implemented and refined in BSD, with many protocols now commonly used by computers.
macOS is a line of open-core graphical operating systems developed, marketed, and sold by Apple Inc., built on technology developed at NeXT through the late 1980s and early 1990s.
z/OS UNIX System Services, built on top of MVS services, cannot run independently, and is used by IBM for FIPS requirements and z/OS components.
Linux is a Unix-like operating system that was developed without any Unix code and is available for study and modification, which resulted in its use on a wide range of computing machinery from supercomputers to smartwatches.
Microsoft Windows is a family of proprietary operating systems designed by Microsoft Corporation and primarily targeted to Intel architecture-based computers.
ReactOS is a Windows alternative operating system that is being developed on the principles of Windows.
Other operating systems are used almost exclusively in academia, for operating systems education or to do research on operating system concepts.
The components of an operating system all exist to make the different parts of a computer work together, including the kernel, program execution, interrupts, and software interrupts.
Interrupts provide an efficient way for most operating systems to react to the environment, and software interrupts are similar to hardware interrupts, but with change away from the currently running process.
Users can send messages to the kernel to modify the behavior of a currently running process.Overview of Operating Systems
INT assembly language instruction used to generate software interrupts for x86 CPUs
Kill system call used to send signals to processes in Unix-like operating systems
Signals used to inform processes of the occurrence of asynchronous events in Unix-like operating systems
Hardware interrupt used to avoid the CPU waiting for I/O completion in computers
Interrupt-driven I/O used when a process causes an interrupt for every character or word transmitted
Direct Memory Access (DMA) used to allow devices to access main memory directly without interrupting the CPU
Modern CPUs support multiple modes of operation, including user mode and supervisor mode
Memory management in operating systems involves managing all system memory in use by programs
Virtual memory addressing allows the kernel to choose what memory each program may use at any given time
Multitasking refers to the running of multiple independent computer programs on the same computer
File systems used to structure files on disks to allow for faster access, higher reliability, and better use of available space
Virtual File System (VFS) allows an operating system to provide programs with access to an unlimited number of devices with an infinite variety of file systems installed on themOperating System Overview
Linux and UNIX allow any file system to be used regardless of the media it is stored in
Device drivers translate operating system mandated function calls into device specific calls
Networking protocols allow computers running dissimilar operating systems to participate in a common network
Security of operating systems has long been a concern because of highly sensitive data held on computers
An operating system provides a user interface for human interaction
Graphical user interfaces are not an operating system service, but incorporating support for one into the operating system kernel can allow the GUI to be more responsive
Real-time operating systems are intended for applications with fixed deadlines
Hobby operating systems are classified as those whose code has not been directly derived from an existing operating system
Application software is generally written for use on a specific operating system
Unix was the first operating system not written in assembly language, making it portable
Writing applications against software platforms or adopting standards can reduce costs in supporting operating systems diversity
Market share of operating systems varies and is subject to change