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Because of this set of potentially supported OS peripherals always significantly greater range of devices, which OS to manage the installation of a specific machine, the OS valuable feature is the ability to dynamically loaded into RAM required driver (no stop OS) and unload it after the need for support device passed, which could significantly save memory system area. Alternative dynamic loading drivers to change the current configuration of external devices computer is re-compiling the kernel code with the required set of drivers that creates all components of the kernel instead of static dynamic. For example, thus solved the problem in some versions of the operating system UNIX. In static links between kernel and drivers of the OS easier, but this requires source code modules operating system, the availability of which is not likely (for non-UNIX versions), not the rule. In addition, this option works previous version of operating system must be stopped and replaced by a new, and interruptions in the work environment in some applications may not tolerated. Support for dynamic load drivers is almost mandatory for today's universal operating systems. Multiple file systems discs of particular kinds of peripheral devices, as it is for most of them stored as a user or system data. These disks are organized in file systems, and properties of the file system largely determines the properties of the OS is its reliability, performance, maximum storage. The popularity of file system often leads to the migration of "native" environment in other operating systems, such as file system FAT appeared in the original MS-DOS, but it was implemented in OS / 2, a family of MS Windows, and many of UNIX. Because of the support of several popular file systems for the I / O subsystem is also important as support for a wide range of peripheral devices. It is also important that architecture enables I / O subsystem simply include it in new types of file systems without having to re-code. Typically, the operating system has a special layer of software responsible for this task, such as layer VFS (Virtual File System) in the version of UNIX System V code of Release 4. Translate a Web Page Support for synchronous and asynchronous I / O operations I / O operation can be performed on software module, requesting operation in synchronous or asynchronous modes. The meaning of these regimes, the same as described above for system calls-synchronous mode means that the software module suspend its work until the I / O operation is not completed (Figure 7.1, a), and in asynchronous a software module continues to be implemented in conjunction with multiprogrammnom mode operation O (Fig. 7 L, b). The difference however is that the I / O operations can be initiated not only user-process in the case of operations performed by the system call, but the kernel code, such as virtual memory subsystem code readers missing pages in memory. I / O subsystem to provide its clients (user process and kernel code) to perform as synchronous or asynchronous I / O operation, depending on the needs of serious side. System I / O calls are plotted as a synchronous procedure because such operations last long, and the user or process flow still have to wait for the results of operations in order to continue its work. Domestic same challenges of Input / Output from kernel modules usually implemented in the form of asynchronous processes, as well as kernel codes need freedom to choose conduct further inquiry after I / O operations. Using asynchronous procedure leads to a more flexible solutions, as well as through asynchronous call you can always build interpretation, creating further interim procedure, blocking implementation of procedures leading to completion of I / O. Sometimes the application process and the need to implement asynchronous I / O operations, such as architecture mikroyadernoy when part of the code works as a customized application process, but also serves as an operating system for complete freedom of action and after the call I / O operations. Multi I / O subsystem model Overall design A multilayer software, typical for operating systems in general, are especially useful in natural and construction of I / O subsystem. With great diversity I / O devices with significantly different characteristics (printer and CDs, graphical display and network adapter, etc.), a hierarchical structure of software to observe a balance between two very contradictory requirements: on the one hand, it is necessary to take into account all features each device on the other hand, provide a logical presentation and a unified interface for all types of devices. In doing so, the lower layers of I / O subsystem must include individual drivers written for the specific physical devices, and upper management procedures should compile these devices, providing a common interface, if not for all the devices, at least for groups of devices, with some common characteristics such printers for a manufacturer or all matrix printers, etc. Multi structure certainly facilitates the solution of most listed in the previous section of I / O subsystem tasks, such as simplicity of the new drivers, support for multiple file systems, dynamic zagruzka- unloading of drivers and others. Synthesis of the I / O subsystem presented in Fig. 7.2. Of the figure shows that the software I / O shared not only horizontal layers, but the vertical. This is because for such a diverse world, as external devices, it is difficult to ensure uniformity in the splitting of administration sectors. Therefore, the general principle of multi remains fair, but for a certain type of device it is in many ways, with its number of layers and their functions. In the structure of the examples are three vertical subsystem for managing disks, graphics devices, such as monitors, printers and Plotter, and network adapters. Naturally, this list may be added and others, such as management subsystem character terminals or any specialized devices such as analog-to-digital and digital analog converters. Each subsystem has several vertical segments modules. The bottom layer of a so-called hardware device drivers, the title of which reflects the fact that they manage external hardware devices by exchanging byte blocks and bytes, and are usually the case with a high level of the logical organization of data, such as files or complex graphical objects. Options upstream sectors are heavily dependent on the type of vertical subsystem. Manager / O In the I / O subsystem, along with modules, reflecting the specificity of external devices and forming vertical subsystem modules are universal destination. These modules provide a coherent work of all other components of I / O subsystem and interaction with the user processes and other subsystem OS. As management devices, such as organizing distributed on all levels, forming a sheath. This envelope is sometimes called the I / O manager. Objectives of this manager quite diverse. Top Layer Manager of I / O system calls, which take from user processes I / O requests and pereadresuyut them responsible for a certain class of device modules and drivers, and return the results of I / O operations. Thus this layer supports user interface I / O applications programmers to create maximum convenience for manipulating external devices and sharing their data. The lower layer manager has direct interaction with the external controller devices ekraniruya drivers of particular hardware platform computer-tyre I / O, system interruption, etc. This layer takes requests from drivers to exchange data with the controller registers in some synthesis of using independent from a tyre addressing and I / O format, and then translates these requests depending on the hardware platform format. Manager interruption considered above can be part of the I / O manager, or a separate kernel module. In the latter case manager for the I / O controller interrupt performs primary processing requests interruption, conveying the controller general information on the source of the request. An important function of I / O manager is a certain environment for the rest of the subsystem components, which would facilitate their interaction with each other. This can be achieved by establishing a standard internal interface I / O modules interact with each other, which would complement the external interface subsystem applications processes, kernel modules and other equipment. Such interface greatly facilitates the integration of new drivers and file systems to the OS. In addition, developers drivers and other software components are exempt from writing common procedures, such as data buffering, and synchronization of multiple modules are in the exchange of data. All these functions assume I / O manager. Another function of the manager is the I / O modules interface I / O modules with other subsystems of the OS, such as sub-process management, virtual memory, and others. Examples of such manager is the manager of I / O on Windows NT, as well as STREAMS environment, in many versions of the operating system UNIX. Manager O Windows NT organizes interaction between modules via I / O request packet-IRP (I / O Request Packet). After receiving a request from the procedure call system, a manager of IRP and passes it correct driver. After the driver requested operation returns a response in the form of another IRP manager, and he, in turn, may need to refer the IRP another driver. Manager allows drivers to put the relationship (bindings) among themselves, and on the basis of the relationship and transferred packages IRP. In addition, the manager supports Windows NT dynamic zagruzku- unload drivers without stop system. A standard internal mezhmodulnogo interface improves stability and improves I / O subsystem Scales, although some may slow its work, as well as any division into sections and parts leads to additional operations in conjunction compared to monolithic organization with a direct transfer of management.
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