How Operating Systems Work
canada goose clearance More recently, operating systems have started to pop up in smaller computers as well. If you like to tinker with electronic devices, you’re probably pleased that operating systems can now be found on many of the devices we use every day, from cell phones to wireless access points. The computers used in these little devices have gotten so powerful that they can now actually run an operating system and applications. The computer in a typical modern cell phone is now more powerful than a desktop computer from 20 years ago, so this progression makes sense and is a natural development. canada goose clearance
Not all computers have operating systems. The computer that controls the microwave oven in your kitchen, for example, doesn’t need an operating system. It has one set of tasks to perform, very straightforward input to expect (a numbered keypad and a few pre set buttons) and simple, never changing hardware to control. For a computer like this, an operating system would be unnecessary baggage, driving up the development and manufacturing costs significantly and adding complexity where none is required. Instead, canada goose outlet uk the computer in a microwave oven simply runs a single hard wired program all the time.
cheap Canada Goose All desktop computers have operating systems. The most common are the Windows family of operating systems developed by Microsoft, the Macintosh operating systems developed by Apple and the UNIX family of operating systems (which have been developed by a whole history of individuals, corporations and collaborators). There are hundreds of other operating systems available for special purpose applications, including specializations for mainframes, robotics, manufacturing, real time control systems and canada goose outlet buffalo so on. cheap Canada Goose
The first task, managing the hardware and software resources, is very important, as various programs and input methods compete for the attention of the central processing unit (CPU) and demand memory, storage and input/output (I/O) bandwidth for their own purposes. In this capacity, the operating system plays the role of the good parent, making sure that each application gets the necessary resources while playing nicely with all the other applications, as well as husbanding the limited capacity of the system to the greatest good of all the users and applications.
The second task, providing a consistent application interface, is especially important if there is to be more than one of a particular type of computer using the operating system, or if the hardware making up the computer is ever open to change. A consistent application program interface (API) allows a software developer to write an application on one computer and have a high level of confidence that it will run on another computer of the same type, even if the amount of canada goose outlet online memory canada goose outlet in usa or the quantity of storage is different on the two machines.
canada goose black friday sale Even if a particular computer is unique, an operating system can ensure that applications continue to run when hardware upgrades and updates occur. This is because the operating system not the application is charged with managing the hardware and the distribution of its resources. One of the challenges facing developers is keeping their operating systems flexible enough to run hardware from the thousands of vendors manufacturing computer equipment. Today’s systems can accommodate thousands of different printers, disk drives and special peripherals in any possible combination. canada goose black friday sale
Real time operating system (RTOS) Real canada goose outlet shop time operating systems are used to control machinery, scientific instruments and industrial systems. An RTOS typically has very little user interface capability, and no end user utilities, since the system will be a “sealed box” when delivered for use. A very important canada goose outlet in toronto part of an RTOS is managing the resources of the computer so that canada goose outlet seattle a particular operation executes in precisely the same amount of time, every time it occurs. Microsoft’s Windows and Apple’s MacOS platforms are both examples of operating systems that will let a single user have several programs in operation canada goose outlet miami at the same time. The operating system must canada goose outlet 2015 make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources canada goose jacket outlet so that a problem with one user doesn’t affect the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of multi user operating systems.
It’s important to differentiate between multi canada goose outlet toronto user operating systems and single user operating systems that support networking. Windows 2000 and Novell Netware can each support hundreds or thousands of networked users, but the operating systems themselves aren’t true multi user operating systems. The system administrator is the only “user” for Windows 2000 or Netware. The network support and all of the remote user logins the network enables are, in the overall canada goose sale uk plan of the operating system, a program being run by the administrative user.
Canada Goose Outlet When you turn on the power to a computer, the first program canada goose jacket uk that runs canada goose outlet in montreal is usually a set of instructions kept in the computer’s read only memory (ROM). This code examines the system hardware to make sure everything is functioning properly. This power on self test (POST) checks the CPU, memory, and basic input output systems (BIOS) for errors and stores the result in a special memory location. Once the POST has successfully completed, the software loaded in ROM canada goose outlet (sometimes called the BIOS or firmware) will begin to activate the computer’s disk drives. In most modern computers, when the computer activates the hard disk drive, it finds the first piece of the operating system: the bootstrap loader. Canada Goose Outlet
canada goose store The bootstrap loader is a small program that has a single function: It loads the operating system into memory and allows it to begin operation. In the most basic form, the bootstrap loader sets up the small driver programs that interface with and control the various hardware subsystems of the computer. It sets up the divisions of memory that hold the operating system, user information and applications. It establishes the data structures that will hold the myriad signals, flags and semaphores that are used to communicate within and between the subsystems and applications of the computer. Then it turns canada goose outlet authentic control of the computer over to the operating system. canada goose store
It’s tempting to think of a process as an application, but that gives an incomplete picture of how processes relate to the operating system and hardware. The application you see (word processor, spreadsheet or game) is, indeed, a process, but that application may cause several other processes to begin, for tasks like communications with other devices or other computers. There are also numerous processes that run without giving you direct evidence that they ever exist. For example, Windows XP and UNIX can have dozens of background processes running to handle the network, memory management, disk management, virus checks and so on.
Interrupts are special signals sent by hardware or software to the CPU. It’s as if some part of the computer suddenly raised its hand to ask for the CPU’s attention in a lively meeting. Sometimes the operating system will canada goose jacket outlet uk schedule the priority of processes so that interrupts are masked that is, the operating system will ignore the interrupts from some sources so that a particular job can be finished as quickly as possible. There are some interrupts (such as those from error conditions or problems with memory) that are so important that they can’t be ignored. These non maskable interrupts (NMIs) must be dealt with immediately, regardless of the other tasks at hand.
canada goose While interrupts add some complication to the execution of processes in a single tasking system, the canada goose outlet online reviews job of the operating system becomes much more complicated in a multi tasking system. Now, the operating system must arrange the execution of applications so that you believe that there are several things happening at once. This is complicated because the CPU can only do one thing at a time. Today’s multi core processors and multi processor machines can handle more work, but each processor core is still capable of managing one task at a time. canada goose
A process occupies a certain amount of RAM.
Canada Goose sale Each process has a status canada goose uk site associated with it. Many processes consume no canada goose outlet website legit CPU time until they get some sort of input. For example, a process might be waiting for a keystroke from the user. While it is waiting for the keystroke, it uses no CPU time. While it’s waiting, it is “suspended”. When the keystroke arrives, the OS changes its status. When the status of the process changes, from pending to active, for example, or from suspended to running, the information in the process control block must be used like the data in any other program to direct execution of the task switching portion of the operating system. Canada Goose sale
canada goose coats This process swapping happens without direct user interference, and each process gets enough CPU cycles to accomplish its task in a reasonable amount of time. Trouble can begin if the user tries to have too many processes functioning at the same time. The operating system itself requires some CPU cycles to perform the saving and swapping canada goose victoria parka outlet of all the registers, queues and stacks of the application processes. If enough processes are started, and if the operating system hasn’t been carefully designed, the system can canada goose outlet mall begin to use the vast majority of its available CPU cycles to swap between processes rather than run processes. When this happens, it’s called thrashing, and it usually requires some sort of direct user intervention to stop processes and bring order back to the system. canada goose coats
canada goose coats on sale One way that operating system designers reduce the chance of thrashing is by reducing the need for new processes to perform various tasks. Some operating systems allow for a “process lite,” called a thread, that can deal with all the CPU intensive work of a normal process, but generally does not deal with the various types of I/O and does not establish structures requiring the extensive process control block of a regular process. A process may start many threads or other processes, canada goose outlet uk fake but a thread cannot start a process. canada goose coats on sale
buy canada goose jacket cheap So far, all the scheduling we’ve discussed has concerned a single CPU. In a system with two or more CPUs, the operating system must divide the workload among the CPUs, trying to balance the demands of the required processes with the available cycles on the different canada goose outlet winnipeg CPUs. Asymmetric operating systems use one CPU for their own needs and divide application processes among the remaining CPUs. Symmetric operating systems divide themselves among the various CPUs, balancing demand versus CPU availability even when the operating system itself is all that’s running. buy canada goose jacket cheap
As an example, let’s look at an imaginary small system with 1 megabyte (1,000 kilobytes) of RAM. During the boot process, the operating system of our imaginary computer is designed to go to the top of available memory and then “back up” far enough to meet the needs of the operating system itself. Let’s say that canada goose outlet store quebec the operating system needs 300 kilobytes to run. Now, the operating system goes to the bottom of the pool of RAM and starts building up with the various driver software required to control the hardware subsystems of the computer. In our imaginary computer, the drivers take up 200 kilobytes. So after getting the operating system completely loaded, there are 500 kilobytes remaining for application processes.
When applications begin to be loaded into memory, they canada goose outlet eu are loaded in block sizes determined by the operating system. If the block size is 2 kilobytes, then every process that’s loaded will be given a chunk of memory that’s a multiple of 2 kilobytes in size. Applications will be loaded in these fixed block sizes, with the blocks starting and ending on boundaries established by words of 4 or 8 bytes. These blocks and boundaries help to ensure that applications won’t be loaded on top of one another’s space by a poorly calculated bit or two. With that ensured, the larger question is what to do when the 500 kilobyte application space is filled.
In most computers, it’s possible to add memory beyond the original capacity. For example, you might expand RAM from 1 to 2 gigabytes. This works fine, but can be relatively expensive. It also ignores a fundamental fact of computing most of the information that an application stores in memory is not being used at any given moment. A processor can only access memory one location at a time, canada goose outlet store uk so the vast majority of RAM is unused at any moment. Since disk space is cheap compared to RAM, then moving information in RAM to hard disk can greatly expand RAM space at no cost. This technique is called virtual memory management.
canada goose clearance sale High speed cache This is fast, relatively small amounts of memory that are available to the CPU through the fastest connections. canada goose clearance sale
canadian goose jacket The path between the operating system and virtually all hardware not on the computer’s motherboard goes through a special program called a driver. Much of a driver’s function is to be the translator between the electrical signals of the hardware subsystems and the high level programming languages of the operating system and application programs. Drivers take data that the operating system has defined as a file and translate them into streams of bits placed in specific locations on storage devices, or a series of laser pulses in a printer. canadian goose jacket
Canada Goose Parka One reason that drivers are separate from the operating system is so that new functions can be added to the driver and thus to the hardware subsystems without requiring the operating system itself to be modified, recompiled and redistributed. Through the development of new hardware device drivers, development often performed or paid for by the manufacturer of the subsystems rather than the publisher of the operating system, input/output capabilities of the overall system can be greatly enhanced. Canada Goose Parka
canada goose deals Managing input and output is largely a matter of managing queues and buffers, special storage facilities that take a stream of bits from a device, perhaps a keyboard or a serial port, hold those bits, and release them to the CPU at a rate with which the CPU can cope. This function is especially important when a number of processes are running and taking up processor time. The operating system will instruct a buffer to continue taking input from the device, but to stop sending data to the CPU while the process using the input is suspended. Then, when the process requiring input is made active once again, the operating system will command the buffer to send data. This process allows a keyboard or a modem to deal with external users or computers at a high speed even though canada goose outlet legit there are times when the CPU can’t use input from those sources. canada goose deals
In this example, the instruction tells the operating system to create a file that will allow random access to its data (signified by the 1 the other option might be 0 for a serial file), will have a name typed in by the user (%Name) and will be a size that varies depending on canada goose outlet in new york how much data is stored in the file (signified by the 2 other options might be zero for a fixed size, and 1 for a file that grows as data is added but does not shrink when data is removed). Now, let’s look at what the operating system does to turn the instruction into action.
Canada Goose online APIs have become one of the canada goose outlet online store review most hotly contested areas of the computer industry in recent years. Companies realize that programmers using their API will ultimately translate this into the ability to control and profit from a particular part of the industry. This is one of the reasons that so many companies have been willing to provide applications like readers or viewers to the public at no charge. They know consumers will request that programs take advantage of the free readers, and application companies will be ready to pay royalties to allow their software to provide the functions requested by the consumers. Canada Goose online
buy canada goose jacket Just as the API provides a consistent way for applications to use the resources of the computer system, a user interface (UI) brings structure to http://www.canadagoosesalesus.com the interaction between a user and the computer. In the last canada goose outlet kokemuksia decade, almost all development in user interfaces has been in the area of the graphical user interface (GUI), with two models, Apple’s Macintosh and Microsoft’s Windows, receiving most of the attention and gaining most of the market share. The popular open source Linux operating system also supports a graphical user interface. buy canada goose jacket
Unix, for example, has user interfaces called shells that present a user interface more flexible and powerful than the standard operating system text based interface. Programs such as the Korn Shell and the C Shell are text based interfaces that add important utilities, but their main purpose is to make it easier for the user to manipulate the functions of the operating system. There are also graphical user interfaces, such as X Windows and Gnome, that make Unix and Linux more like Windows and Macintosh computers from the user’s point of view.