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Saturday, April 13, 2013

What are different components of operating system? – Part 4

8. Disk access and file systems: 
- Through this component of the operating system, the users as well as the programs they use are able to sort and organize files on a computer system. 
This is done through the use of folders or directories. 
- This is another central feature of the operating systems. 
- Data is stored by the computers on disks in the form of files which are then structured in some certain predefined ways so as to enable faster access, better use of available memory and higher reliability. 
- These specific ways of the storing the data on disk together constitute the file system. 
- This makes it possible to assign names and attributes to the files. 
- This in turn helps in maintaining the hierarchy of directories and folders in the directory tree. 
- Only one type of file system and one disk drive was supported by the old operating systems. 
- Those file systems had a limited capacity in terms of directory structures and file names that could be used and speed. 
- These limitations were actually the reflection of the operating system’s limitations making it difficult for it to support multiple file systems. 
- There are other simple operating systems that have a limited range of storage accessing options.
- On the other hand Unix and Linux like operating systems support the VFS technology or virtual file system. 
- Unix offers support for a wide range of storage devices irregardless of their file system or design. 
- This enables them to be accessed via a common API (application programming interface). 
- For programs this avoids the need of having knowledge about the devices which they may require to access.
- With virtual file system, the OS can provide access of unlimited devices to the programs having many file systems operating in them.
- This it does through the use of file system drivers and other device drivers. 
- A device driver lets you access a connected storage device such as flash drives. 
- Every drive has a specific language which is only understood by the device driver and it translates it in to a standard one used by the OS for accessing the drives.
- The contents of the drive can be accessed by the kernel only if the device driver is in place. 
- The purpose of the file system driver is to translate the commands used for accessing the file systems in to the standard set recognized by the operating system. 
- These file systems are then dealt by the programs based on their directories or folders and file names organized in hierarchy. 
- These files can be created, deleted or modified by the programs.

9. Device Drivers: 
- This specifically developed computer software enables the interaction with the hardware devices. 
- It creates an interface through which communication can be done with the device via communications sub system or bus i.e., the means through which the hardware is connected to the system. 
- This computer program depends up on the hardware but is also specific to the operating system.
- It enables an applications software package running under kernel in order to interact with the hardware device transparently.
- Further, it raises the requisite interrupt required for handling asynchronous time dependent interfacing needs of the hardware. 
- Abstraction is the key goal of the device drivers.
- Every hardware model is different and so the operating system cannot know about how each device will be controlled. 
- The way the devices should be controlled is now dictated by the operating systems as a solution to this problem. 
- Therefore, translating the function calls from the OS into calls specific to the device becomes the purpose of the device drivers. 
- Any device would function properly if a device driver suitable to it is available which will ensure the normal operation of the device from the viewpoint of the OS. 

Read the next post "What are different components of operating system? – Part 5"

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