Device management is another major function of an operating system. In the device management task of the operating is to manage I/O and storage devices such as printers, card readers, tapes, disk and supporting devices such as the control unit and control channel.
The major tasks of the operating system with respect to device management are:
- Track the status of all the devices
- To decide which process gets a device, for how long and where.
There are three different categories of devices. On the basis of these categories, the operating system will decide which process will get which devices and for how long.
- Dedicated Device: are the devices that are assigned to one process at a time. The process releases the device once it is completed, so no pre-emption case occurs here. For example, printer
- Shared Device: are one that can be shared among different processes. These get according to the use and priority. For example, hard disk.
- Virtual Device: are a combination of both shared and dedicated devices. For example, a printer is a dedicated device and can be made sharable using spooling (queue).
There are majorly two types of devices under the categories mentioned above.
- I/O devices: An input device takes data as input from the user and an output device generates output. For example, Keyboard(input), printer(output).
- Storage Devices: It is a mechanism by which the computer stores the information in such a way that information may be retrieved at a later time. For example, Hard disk
The storage devices can be of the following three different types: Serial access, Direct access.
Serial Access Device
This method is also known as a sequential access method. The data is accessed by starting from the beginning, then searched through in sequence, until the required information is found.
This method is very slow. Serial access is used in old magnetic tapes
Direct Access Device
It is also known as a random access device. The system can calculate where exactly the data is stored. The location can be directly accessed.
For example, hard disks, CDs and DVDs are the types of direct access devices.
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