Instead, it was called an "environment" that ran only on computers with the MS-DOS operating system. Microsoft introduced Windows version 1.0 in 1985, but it was not a real operating system because it acted merely as an interface between the user and the real operating system. The Macintosh was the first widely used computer with a GUI, which in turn was based on a desktop created by Xerox. Most modern operating systems feature a menu-driven graphical user interface (GUI), which is pronounced "gooey," with menus, icons, and task bars. Network resources usually include both hardware (such as CPUs, memory areas, printers, disk drives, modems, and tape drives) and software (such as application programs and data files). Operating systems with networking capability have a fifth element called the network manager, which provides a convenient way for users to share resources. The file manager also controls the amount of flexibility each user is allowed with that file (such as read-only, read-and-write-only, or the authority to create and/or delete records). It is based on predetermined access policies to enforce the correct security for each file so that files can be accessed only by individual or group users that have permission to do so. The file manager allocates the file by opening it and de-allocates it by closing it. The file manager keeps track of every piece of software in the system, including application programs, data files, directories, etc. The device manager allocates a device, starts its operation, and, finally, de-allocates it. The device manager makes these decisions based on a scheduling policy chosen by the system's designers. The device manager chooses the most efficient way to allocate all of the system's devices, including printers, disk drives, CD-ROMs ( compact disc-read only memory), keyboard, monitor, and so forth. Later, when the process is finished, or the maximum amount of time has expired, the processor manager reclaims the processor so it can be allocated again. For example, the processor manager monitors whether the CPU is executing a process or waiting for a READ or WRITE command to finish execution. The processor manager decides how to allocate the central processing unit (CPU) and keep track of the status of each executable step of every program (called a process or task). One of the manager's primary responsibilities is to preserve the part of main memory that is occupied by the operating system itself -it cannot allow any part of it to be altered accidentally or intentionally. Finally, when the time comes to reclaim the memory, the memory manager de-allocates the memory space. In a multi-user environment, the memory manager sets up a table to keep track of who is using which section of memory. It checks the validity of each request for memory space and, if it is a legal request, the memory manager allocates a portion that is not already in use. The memory manager is in charge of main memory, also known as random access memory (RAM). For example, they must be able to monitor their resources continuously, enforce the policies that determine who gets what, when, and how much, allocate their resources when it is appropriate, and de-allocate their resources -reclaim them -when appropriate. They must also be able to work harmoniously with every other manager. These virtual managers must do more than perform their individual tasks. The user interface -the part of the operating system that communicates with the user -is supported by the other four or five managers. The memory manager, the processor manager, the device manager, and the file manager form the pyramid's base network operating systems add a network manager as well. This does not necessarily mean that the operating system executes the command or sends the error message, but it does control the parts of the system that do.Įvery operating system, regardless of its size and complexity, can be represented by a pyramid showing how its five major functions (called managers) work together. Novell NetWare, UNIX, Windows NT, Windows 2000 Linux, Macintosh OS, MS-DOS, Windows 98, Windows 2000 If it is not executed, the operating system must arrange for the user to receive a message, usually on the monitor, explaining Platform When a computer user sends a command by typing it from the keyboard or clicking with the mouse, the operating system must make sure that the command is executed. In short, it is the boss -without it, nothing can happen. It controls who can use the system and how. To be specific, it controls every file, every device, every section of main memory, every nanosecond of processing time, and every network connection. The operating system is software that manages every part of a computer system -all hardware and all other software.
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