An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the system. At the foundation of all system software, an operating system performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking and managing file systems. Most operating systems come with an application that provides a user interface for managing the operating system, such as a command line interpreter or graphical user interface. The operating system forms a platform for other system software and for application software.
The most commonly-used contemporary desktop and laptop (notebook) OS is Microsoft Windows. More powerful servers often employ Linux, FreeBSD, and other Unix-like systems. However, these operating systems, especially Mac OS X, are also used on personal computers
The most commonly-used contemporary desktop and laptop (notebook) OS is Microsoft Windows. More powerful servers often employ Linux, FreeBSD, and other Unix-like systems. However, these operating systems, especially Mac OS X, are also used on personal computers
Services:
Process management:
Every program running on a computer, be it a service or an application, is a process. As long as a von Neumann architecture is used to build computers, only one process per CPU can be run at a time. Older microcomputer OSes such as MS-DOS did not attempt to bypass this limit, with the exception of interrupt processing, and only one process could be run under them (although DOS itself featured TSR as a very partial and not too easy to use solution).
Most operating systems enable concurrent execution of many processes and programs at once via multitasking, even with one CPU. The mechanism was used in mainframes since the early 1960s, but in the personal computers it became available in 1990s. Process management is an operating system's way of dealing with running those multiple processes. On the most fundamental of computers (those containing one processor with one core) multitasking is done by simply switching processes quickly. Depending on the operating system, as more processes run, either each time slice will become smaller or there will be a longer delay before each process is given a chance to run. Process management involves computing and distributing CPU time as well as other resources. Most operating systems allow a process to be assigned a priority which affects its allocation of CPU time. Interactive operating systems also employ some level of feedback in which the task with which the user is working receives higher priority. Interrupt driven processes will normally run at a very high priority. In many systems there is a background process, such as the System Idle Process in Windows, which will run when no other process is waiting for the CPU.
Most operating systems enable concurrent execution of many processes and programs at once via multitasking, even with one CPU. The mechanism was used in mainframes since the early 1960s, but in the personal computers it became available in 1990s. Process management is an operating system's way of dealing with running those multiple processes. On the most fundamental of computers (those containing one processor with one core) multitasking is done by simply switching processes quickly. Depending on the operating system, as more processes run, either each time slice will become smaller or there will be a longer delay before each process is given a chance to run. Process management involves computing and distributing CPU time as well as other resources. Most operating systems allow a process to be assigned a priority which affects its allocation of CPU time. Interactive operating systems also employ some level of feedback in which the task with which the user is working receives higher priority. Interrupt driven processes will normally run at a very high priority. In many systems there is a background process, such as the System Idle Process in Windows, which will run when no other process is waiting for the CPU.
Memory management:
Current computer architectures arrange the computer's memory in a hierarchical manner, starting from the fastest registers, CPU cache, random access memory and disk storage. An operating system's memory manager coordinates the use of these various types of memory by tracking which one is available, which is to be allocated or deallocated and how to move data between them. This activity, usually referred to as virtual memory management, increases the amount of memory available for each process by making the disk storage seem like main memory. There is a speed penalty associated with using disks or other slower storage as memory – if running processes require significantly more RAM than is available, the system may start thrashing. This can happen either because one process requires a large amount of RAM or because two or more processes compete for a larger amount of memory than is available. This then leads to constant transfer of each process's data to slower storage.
Another important part of memory management is managing virtual addresses. If multiple processes are in memory at once, they must be prevented from interfering with each other's memory (unless there is an explicit request to utilise shared memory). This is achieved by having separate address spaces. Each process sees the whole virtual address space, typically from address 0 up to the maximum size of virtual memory, as uniquely assigned to it. The operating system maintains a page table that match virtual addresses to physical addresses. These memory allocations are tracked so that when a process terminates, all memory used by that process can be made available for other processes.
The operating system can also write inactive memory pages to secondary storage. This process is called "paging" or "swapping" – the terminology varies between operating systems.
It is also typical for operating systems to employ otherwise unused physical memory as a page cache; requests for data from a slower device can be retained in memory to improve performance. The operating system can also pre-load the in-memory cache with data that may be requested by the user in the near future; SuperFetch is an example of this.
Another important part of memory management is managing virtual addresses. If multiple processes are in memory at once, they must be prevented from interfering with each other's memory (unless there is an explicit request to utilise shared memory). This is achieved by having separate address spaces. Each process sees the whole virtual address space, typically from address 0 up to the maximum size of virtual memory, as uniquely assigned to it. The operating system maintains a page table that match virtual addresses to physical addresses. These memory allocations are tracked so that when a process terminates, all memory used by that process can be made available for other processes.
The operating system can also write inactive memory pages to secondary storage. This process is called "paging" or "swapping" – the terminology varies between operating systems.
It is also typical for operating systems to employ otherwise unused physical memory as a page cache; requests for data from a slower device can be retained in memory to improve performance. The operating system can also pre-load the in-memory cache with data that may be requested by the user in the near future; SuperFetch is an example of this.
other tasks will be covered in next articles.
No comments :
Post a Comment