Os capability enhancement software there are several

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Unformatted text preview: f data from/to a disk is much faster than reading/writing from/to a slow I/O device resulting in considerable reduction in CPU idle time during I/O operations involving slow devices. In most computer systems, special low-cost I/O processors are used for spooling the input data from a slow input device on to the disk or for outputting the spooled output data from the disk on to the slow output device. These I/O processors function independent of the main processor (CPU). This enables the main highspeed, expensive CPU to be fully devoted to main computing jobs. The process of spooling is transparent to the user programs. In general, spooling makes better use of both the main memory and the CPU. Dealing with Mutually Exclusive I/O Devices There are several I/O devices that have to be used in dedicated mode for correct system operation. Such devices are called mutually exclusive devices. Printer is a typical example of such a device. For effective utilization of such devices, an operating system often converts them into non-mutually exclusive virtual devices by using spooling. For this, the operating system creates a special process, called a daemon, and a special directory, called a spooling directory. Now when a process makes a request to use the printer, instead of allocating the printer to the process, the operating system opens a file for the process's output data in the spooling directory, which is stored on the disk. All output data to be printed on the printer by the process is written in this file. The file ii closed when the process completes printing. The daemon then actually prints the file from the disk on to the printer. The daemon is the only process having permission to print the files in the spooling directory on to the printer. By protecting the printer against direct use by the users, the problem of having someone keeping it open unnecessarily long is eliminated. Printer is not the only device that can benefit from spooling in this manner. For example, file transfer over a network often uses a network daemon. To send a file somewhere, the system puts it in a network spooling directory on the disk. Later on, the network daemon takes it out from the dire...
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