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67-477: The frequency is accelerated when the operating system requests the highest performance state of the processor. Processor performance states are defined by the Advanced Configuration and Power Interface (ACPI) specification, an open standard supported by all major operating systems; no additional software or drivers are required to support the technology. The design concept behind Turbo Boost

134-420: A disk drive , is considered I/O. The CPU and its supporting circuitry may provide memory-mapped I/O that is used in low-level computer programming , such as in the implementation of device drivers , or may provide access to I/O channels . An I/O algorithm is one designed to exploit locality and perform efficiently when exchanging data with a secondary storage device, such as a disk drive. An I/O interface

201-428: A system call to perform a block I/O write operation, then the system call might execute the following instructions: While the writing takes place, the operating system will context switch to other processes as normal. When the device finishes writing, the device will interrupt the currently running process by asserting an interrupt request . The device will also place an integer onto the data bus. Upon accepting

268-429: A CPU is required. Higher-level operating system and programming facilities employ separate, more abstract I/O concepts and primitives . For example, most operating systems provide application programs with the concept of files . Most programming languages provide I/O facilities either as statements in the language or as functions in a standard library for the language. An alternative to special primitive functions

335-645: A computer even if they are not compatible with the base operating system. A library operating system (libOS) is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with a single application and configuration code to construct a unikernel : a specialized (only the absolute necessary pieces of code are extracted from libraries and bound together ), single address space , machine image that can be deployed to cloud or embedded environments. The operating system code and application code are not executed in separated protection domains (there

402-585: A development of MULTICS for a single user. Because UNIX's source code was available, it became the basis of other, incompatible operating systems, of which the most successful were AT&T 's System V and the University of California 's Berkeley Software Distribution (BSD). To increase compatibility, the IEEE released the POSIX standard for operating system application programming interfaces (APIs), which

469-563: A device traditionally considered as an output device may provide status data (e.g., low toner, out of paper, paper jam). In computer architecture, the combination of the CPU and main memory , to which the CPU can read or write directly using individual instructions , is considered the brain of a computer. Any transfer of information to or from the CPU/memory combo, for example by reading data from

536-475: A function of the number of active cores. When the operating system instructed one of the active cores to enter C3 sleep state using the Advanced Configuration and Power Interface (ACPI), the other active core(s) dynamically accelerated to a higher frequency. Intel Turbo Boost Technology Monitor, as a GUI utility, could be used to monitor Turbo Boost; this utility has reached the end-of-life state by no longer supporting Intel processors released after Q2 2013, and

603-484: A large legal settlement was paid. In the twenty-first century, Windows continues to be popular on personal computers but has less market share of servers. UNIX operating systems, especially Linux, are the most popular on enterprise systems and servers but are also used on mobile devices and many other computer systems. On mobile devices, Symbian OS was dominant at first, being usurped by BlackBerry OS (introduced 2002) and iOS for iPhones (from 2007). Later on,

670-442: A library with no protection between applications, such as eCos . A hypervisor is an operating system that runs a virtual machine . The virtual machine is unaware that it is an application and operates as if it had its own hardware. Virtual machines can be paused, saved, and resumed, making them useful for operating systems research, development, and debugging. They also enhance portability by enabling applications to be run on

737-447: A malformed machine instruction . However, the most common error conditions are division by zero and accessing an invalid memory address . Users can send messages to the kernel to modify the behavior of a currently running process. For example, in the command-line environment , pressing the interrupt character (usually Control-C ) might terminate the currently running process. To generate software interrupts for x86 CPUs,

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804-464: A new feature incorporated into Nehalem-based processors released in the same month. A similar feature called Intel Dynamic Acceleration (IDA) was first available with Core 2 Duo, which was based on the Santa Rosa platform and was released on May 10, 2007. This feature did not receive the marketing treatment given to Turbo Boost. Intel Dynamic Acceleration dynamically changed the core frequency as

871-455: A particular application's memory is stored, or even whether or not it has been allocated yet. In modern operating systems, memory which is accessed less frequently can be temporarily stored on a disk or other media to make that space available for use by other programs. This is called swapping , as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand. Virtual memory provides

938-605: A processor can boost to a higher frequency for a few seconds. These limits are configurable in software for unlocked processors. Some motherboard vendors intentionally use values higher than Intel's default for performance, causing the processor to exceed its thermal design power (TDP). Some Intel Core X Processors and some newer Intel Core Processors (e.g. 10th Gen Desktop Core i7 ) support Intel Turbo Boost Max 3.0 Technology. Newer version Windows 10 and Linux kernel support Intel Turbo Boost Max 3.0 Technology. An Intel November 2008 white paper discusses "Turbo Boost" technology as

1005-503: A program does not interfere with memory already in use by another program. Since programs time share, each program must have independent access to memory. Cooperative memory management, used by many early operating systems, assumes that all programs make voluntary use of the kernel 's memory manager, and do not exceed their allocated memory. This system of memory management is almost never seen any more, since programs often contain bugs which can cause them to exceed their allocated memory. If

1072-408: A program fails, it may cause memory used by one or more other programs to be affected or overwritten. Malicious programs or viruses may purposefully alter another program's memory, or may affect the operation of the operating system itself. With cooperative memory management, it takes only one misbehaved program to crash the system. Memory protection enables the kernel to limit a process' access to

1139-440: A program tries to access memory that is not accessible memory, but nonetheless has been allocated to it, the kernel is interrupted (see § Memory management ) . This kind of interrupt is typically a page fault . When the kernel detects a page fault it generally adjusts the virtual memory range of the program which triggered it, granting it access to the memory requested. This gives the kernel discretionary power over where

1206-469: A representation that human users can understand. From the human user 's perspective, the process of reading or seeing these representations is receiving output; this type of interaction between computers and humans is studied in the field of human–computer interaction . A further complication is that a device traditionally considered an input device, e.g., card reader, keyboard, may accept control commands to, e.g., select stacker, display keyboard lights, while

1273-421: A significant amount of CPU time. Direct memory access (DMA) is an architecture feature to allow devices to bypass the CPU and access main memory directly. (Separate from the architecture, a device may perform direct memory access to and from main memory either directly or via a bus.) When a computer user types a key on the keyboard, typically the character appears immediately on the screen. Likewise, when

1340-402: A specific moment in time. Hard real-time systems require exact timing and are common in manufacturing , avionics , military, and other similar uses. With soft real-time systems, the occasional missed event is acceptable; this category often includes audio or multimedia systems, as well as smartphones. In order for hard real-time systems be sufficiently exact in their timing, often they are just

1407-417: A user moves a mouse , the cursor immediately moves across the screen. Each keystroke and mouse movement generates an interrupt called Interrupt-driven I/O . An interrupt-driven I/O occurs when a process causes an interrupt for every character or word transmitted. Devices such as hard disk drives , solid-state drives , and magnetic tape drives can transfer data at a rate high enough that interrupting

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1474-453: A variation of the classic reader/writer problem . The writer receives a pipe from the shell for its output to be sent to the reader's input stream. The command-line syntax is alpha | bravo . alpha will write to the pipe when its computation is ready and then sleep in the wait queue. bravo will then be moved to the ready queue and soon will read from its input stream. The kernel will generate software interrupts to coordinate

1541-562: Is remote direct memory access , which enables each CPU to access memory belonging to other CPUs. Multicomputer operating systems often support remote procedure calls where a CPU can call a procedure on another CPU, or distributed shared memory , in which the operating system uses virtualization to generate shared memory that does not physically exist. A distributed system is a group of distinct, networked computers—each of which might have their own operating system and file system. Unlike multicomputers, they may be dispersed anywhere in

1608-484: Is a change away from the currently running process. Similarly, both hardware and software interrupts execute an interrupt service routine . Software interrupts may be normally occurring events. It is expected that a time slice will occur, so the kernel will have to perform a context switch . A computer program may set a timer to go off after a few seconds in case too much data causes an algorithm to take too long. Software interrupts may be error conditions, such as

1675-400: Is commonly referred to as "dynamic overclocking ". When the workload on the processor calls for faster performance, the processor's clock will try to increase the operating frequency in regular increments as required to meet demand. The increased clock rate is limited by the processor's power , current , and thermal limits, the number of cores currently in use, and the maximum frequency of

1742-422: Is difficult to define, but has been called "the layer of software that manages a computer's resources for its users and their applications ". Operating systems include the software that is always running, called a kernel —but can include other software as well. The two other types of programs that can run on a computer are system programs —which are associated with the operating system, but may not be part of

1809-513: Is no longer available. Operating system An operating system ( OS ) is system software that 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 , peripherals, and other resources. For hardware functions such as input and output and memory allocation ,

1876-443: Is only a single application running, at least conceptually, so there is no need to prevent interference between applications) and OS services are accessed via simple library calls (potentially inlining them based on compiler thresholds), without the usual overhead of context switches , in a way similarly to embedded and real-time OSes. Note that this overhead is not negligible: to the direct cost of mode switching it's necessary to add

1943-502: Is required whenever the I/O device is driven by a processor. Typically a CPU communicates with devices via a bus . The interface must have the necessary logic to interpret the device address generated by the processor. Handshaking should be implemented by the interface using appropriate commands (like BUSY, READY, and WAIT), and the processor can communicate with an I/O device through the interface. If different data formats are being exchanged,

2010-499: Is supported by most UNIX systems. MINIX was a stripped-down version of UNIX, developed in 1987 for educational uses, that inspired the commercially available, free software Linux . Since 2008, MINIX is used in controllers of most Intel microchips , while Linux is widespread in data centers and Android smartphones. The invention of large scale integration enabled the production of personal computers (initially called microcomputers ) from around 1980. For around five years,

2077-473: Is that they do not load user-installed software. Consequently, they do not need protection between different applications, enabling simpler designs. Very small operating systems might run in less than 10 kilobytes , and the smallest are for smart cards . Examples include Embedded Linux , QNX , VxWorks , and the extra-small systems RIOT and TinyOS . A real-time operating system is an operating system that guarantees to process events or data by or at

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2144-469: Is the I/O monad , which permits programs to just describe I/O, and the actions are carried out outside the program. This is notable because the I/O functions would introduce side-effects to any programming language, but this allows purely functional programming to be practical. The I/O facilities provided by operating systems may be record-oriented , with files containing records , or stream-oriented, with

2211-435: Is the part of the operating system that provides protection between different applications and users. This protection is key to improving reliability by keeping errors isolated to one program, as well as security by limiting the power of malicious software and protecting private data, and ensuring that one program cannot monopolize the computer's resources. Most operating systems have two modes of operation: in user mode ,

2278-542: The CP/M (Control Program for Microcomputers) was the most popular operating system for microcomputers. Later, IBM bought the DOS (Disk Operating System) from Microsoft . After modifications requested by IBM, the resulting system was called MS-DOS (MicroSoft Disk Operating System) and was widely used on IBM microcomputers. Later versions increased their sophistication, in part by borrowing features from UNIX. Apple 's Macintosh

2345-504: The INT assembly language instruction is available. The syntax is INT X , where X is the offset number (in hexadecimal format) to the interrupt vector table . To generate software interrupts in Unix-like operating systems, the kill(pid,signum) system call will send a signal to another process. pid is the process identifier of the receiving process. signum is

2412-498: The personal computer market, as of September 2024 , Microsoft Windows holds a dominant market share of around 73%. macOS by Apple Inc. is in second place (15%), Linux is in third place (5%), and ChromeOS is in fourth place (2%). In the mobile sector (including smartphones and tablets ), as of September 2023 , Android's share is 68.92%, followed by Apple's iOS and iPadOS with 30.42%, and other operating systems with .66%. Linux distributions are dominant in

2479-420: The transistor in the mid-1950s, mainframes began to be built. These still needed professional operators who manually do what a modern operating system would do, such as scheduling programs to run, but mainframes still had rudimentary operating systems such as Fortran Monitor System (FMS) and IBSYS . In the 1960s, IBM introduced the first series of intercompatible computers ( System/360 ). All of them ran

2546-410: The CPU for every byte or word transferred, and having the CPU transfer the byte or word between the device and memory, would require too much CPU time. Data is, instead, transferred between the device and memory independently of the CPU by hardware such as a channel or a direct memory access controller; an interrupt is delivered only when all the data is transferred. If a computer program executes

2613-474: The CPU to re-enter supervisor mode , placing the kernel in charge. This is called a segmentation violation or Seg-V for short, and since it is both difficult to assign a meaningful result to such an operation, and because it is usually a sign of a misbehaving program, the kernel generally resorts to terminating the offending program, and reports the error. Windows versions 3.1 through ME had some level of memory protection, but programs could easily circumvent

2680-542: The active cores. Turbo-Boost-enabled processors are the Core i3 , Core i5 , Core i7 , Core i9 and Xeon series manufactured since 2008, more particularly, those based on the Nehalem , and later microarchitectures . Frequency increases occur in increments of 133 MHz for Nehalem processors and 100 MHz for Sandy Bridge, Ivy Bridge, Haswell and Skylake processors. When any electrical or thermal limits are exceeded,

2747-538: The application program, which then interacts with the user and with hardware devices. However, in some systems an application can request that the operating system execute another application within the same process, either as a subroutine or in a separate thread, e.g., the LINK and ATTACH facilities of OS/360 and successors . An interrupt (also known as an abort , exception , fault , signal , or trap ) provides an efficient way for most operating systems to react to

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2814-453: The computer's memory. Various methods of memory protection exist, including memory segmentation and paging . All methods require some level of hardware support (such as the 80286 MMU), which does not exist in all computers. In both segmentation and paging, certain protected mode registers specify to the CPU what memory address it should allow a running program to access. Attempts to access other addresses trigger an interrupt, which causes

2881-471: The details of how interrupt service routines behave vary from operating system to operating system. However, several interrupt functions are common. The architecture and operating system must: A software interrupt is a message to a process that an event has occurred. This contrasts with a hardware interrupt — which is a message to the central processing unit (CPU) that an event has occurred. Software interrupts are similar to hardware interrupts — there

2948-422: The environment. Interrupts cause the central processing unit (CPU) to have a control flow change away from the currently running program to an interrupt handler , also known as an interrupt service routine (ISR). An interrupt service routine may cause the central processing unit (CPU) to have a context switch . The details of how a computer processes an interrupt vary from architecture to architecture, and

3015-462: The file containing a stream of bytes. Channel I/O requires the use of instructions that are specifically designed to perform I/O operations. The I/O instructions address the channel or the channel and device; the channel asynchronously accesses all other required addressing and control information. This is similar to DMA, but more flexible. Port-mapped I/O also requires the use of special I/O instructions. Typically one or more ports are assigned to

3082-410: The hardware checks that the software is only executing legal instructions, whereas the kernel has unrestricted powers and is not subject to these checks. The kernel also manages memory for other processes and controls access to input/output devices. The operating system provides an interface between an application program and the computer hardware, so that an application program can interact with

3149-493: The hardware only by obeying rules and procedures programmed into the operating system. The operating system is also a set of services which simplify development and execution of application programs. Executing an application program typically involves the creation of a process by the operating system kernel , which assigns memory space and other resources, establishes a priority for the process in multi-tasking systems, loads program binary code into memory, and initiates execution of

3216-418: The indirect pollution of important processor structures (like CPU caches , the instruction pipeline , and so on) which affects both user-mode and kernel-mode performance. The first computers in the late 1940s and 1950s were directly programmed either with plugboards or with machine code inputted on media such as punch cards , without programming languages or operating systems. After the introduction of

3283-444: The interface must be able to convert serial data to parallel form and vice versa. Because it would be a waste for a processor to be idle while it waits for data from an input device there must be provision for generating interrupts and the corresponding type numbers for further processing by the processor if required. A computer that uses memory-mapped I/O accesses hardware by reading and writing to specific memory locations, using

3350-404: The interrupt request, the operating system will: When the writing process has its time slice expired, the operating system will: With the program counter now reset, the interrupted process will resume its time slice. Among other things, a multiprogramming operating system kernel must be responsible for managing all system memory which is currently in use by the programs. This ensures that

3417-431: The kernel—and applications—all other software. There are three main purposes that an operating system fulfills: With multiprocessors multiple CPUs share memory. A multicomputer or cluster computer has multiple CPUs, each of which has its own memory . Multicomputers were developed because large multiprocessors are difficult to engineer and prohibitively expensive; they are universal in cloud computing because of

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3484-400: The memory allocated to a different one. Around the same time, teleprinters began to be used as terminals so multiple users could access the computer simultaneously. The operating system MULTICS was intended to allow hundreds of users to access a large computer. Despite its limited adoption, it can be considered the precursor to cloud computing . The UNIX operating system originated as

3551-408: The need to use it. A general protection fault would be produced, indicating a segmentation violation had occurred; however, the system would often crash anyway. The use of virtual memory addressing (such as paging or segmentation) means that the kernel can choose what memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks. If

3618-408: The open-source Android operating system (introduced 2008), with a Linux kernel and a C library ( Bionic ) partially based on BSD code, became most popular. The components of an operating system are designed to ensure that various parts of a computer function cohesively. With the de facto obsoletion of DOS , all user software must interact with the operating system to access hardware. The kernel

3685-561: The operating frequency automatically decreases in decrements of 133 or 100 MHz until the processor is again operating within its design limits. Turbo Boost 2.0 was introduced in 2011 with the Sandy Bridge microarchitecture, while Intel Turbo Boost Max 3.0 was introduced in 2016 with the Broadwell-E microarchitecture . A feature of Turbo Boost 2.0 is that it introduced time windows with different levels of power limits, so that

3752-420: The operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers . In

3819-421: The piping. Signals may be classified into 7 categories. The categories are: Input/output (I/O) devices are slower than the CPU. Therefore, it would slow down the computer if the CPU had to wait for each I/O to finish. Instead, a computer may implement interrupts for I/O completion, avoiding the need for polling or busy waiting. Some computers require an interrupt for each character or word, costing

3886-417: The programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there. Input and output In computing , input/output ( I/O , i/o , or informally io or IO ) is the communication between an information processing system, such as a computer , and the outside world, such as another computer system, peripherals, or a human operator. Inputs are

3953-413: The same assembly language instructions that computer would normally use to access memory. An alternative method is via instruction-based I/O which requires that a CPU have specialized instructions for I/O. Both input and output devices have a data processing rate that can vary greatly. With some devices able to exchange data at very high speeds direct access to memory (DMA) without the continuous aid of

4020-418: The same operating system— OS/360 —which consisted of millions of lines of assembly language that had thousands of bugs . The OS/360 also was the first popular operating system to support multiprogramming , such that the CPU could be put to use on one job while another was waiting on input/output (I/O). Holding multiple jobs in memory necessitated memory partitioning and safeguards against one job accessing

4087-619: The server and supercomputing sectors. Other specialized classes of operating systems (special-purpose operating systems), such as embedded and real-time systems, exist for many applications. Security-focused operating systems also exist. Some operating systems have low system requirements (e.g. light-weight Linux distribution ). Others may have higher system requirements. Some operating systems require installation or may come pre-installed with purchased computers ( OEM -installation), whereas others may run directly from media (i.e. live CD ) or flash memory (i.e. USB stick). An operating system

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4154-400: The signal number (in mnemonic format) to be sent. (The abrasive name of kill was chosen because early implementations only terminated the process.) In Unix-like operating systems, signals inform processes of the occurrence of asynchronous events. To communicate asynchronously, interrupts are required. One reason a process needs to asynchronously communicate to another process solves

4221-614: The signals or data received by the system and outputs are the signals or data sent from it. The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation . I/O devices are the pieces of hardware used by a human (or other system) to communicate with a computer. For instance, a keyboard or computer mouse is an input device for a computer, while monitors and printers are output devices . Devices for communication between computers, such as modems and network cards , typically perform both input and output operations. Any interaction with

4288-400: The size of the machine needed. The different CPUs often need to send and receive messages to each other; to ensure good performance, the operating systems for these machines need to minimize this copying of packets . Newer systems are often multiqueue —separating groups of users into separate queues —to reduce the need for packet copying and support more concurrent users. Another technique

4355-488: The system by an interactor is an input and the reaction the system responds is called the output. The designation of a device as either input or output depends on perspective. Mice and keyboards take physical movements that the human user outputs and convert them into input signals that a computer can understand; the output from these devices is the computer's input. Similarly, printers and monitors take signals that computers output as input, and they convert these signals into

4422-473: The world. Middleware , an additional software layer between the operating system and applications, is often used to improve consistency. Although it functions similarly to an operating system, it is not a true operating system. Embedded operating systems are designed to be used in embedded computer systems , whether they are internet of things objects or not connected to a network. Embedded systems include many household appliances. The distinguishing factor

4489-406: Was the first popular computer to use a graphical user interface (GUI). The GUI proved much more user friendly than the text-only command-line interface earlier operating systems had used. Following the success of Macintosh, MS-DOS was updated with a GUI overlay called Windows . Windows later was rewritten as a stand-alone operating system, borrowing so many features from another ( VAX VMS ) that

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