File-System provides the mechanism for on-line storage and access to the file contents, including data and programs. The file system resides permanently on secondary, which is design to hold a large amount of data permanently.
File-System Structure –
Disks provide most of the secondary storage on which file systems are main-train. 2 characteristics create them convenient for this purpose:
- A disk will be rewritten in place; it’s attainable to browse a block from the disk, modify the block, and write it back to an equivalent place.
- A disk will access directly any block of data it contains. Thus it is simple to access any file either sequentially or randomly. And switching from one file to another requires only moving the read-write heads and waiting for the disk to rotate.
To improve I/O efficiency, I/O transfers between memory and disk are perform in unit of blocks. Each has one or more sectors. counting on the drive, sector size varies from thirty two bytes to four,096 bytes; the standard size is 512 bytes.
File-systems give economical and convenient access to the disk by permitting information to be stores, locates, and retrives simply.
A filing system poses 2 quite totally different style issues. The primary downside is shaping however the filing system ought to look to the user. This task involves defining a file and its attributes, the operations aloowed on a fire, and the directory structure for organizing files.
The file system itself is generally compose of many different levels. The I/O control level consists of device and interrupt handlers to transfer information between the main memory and the disk system. A device driver can be thought of as translator. Its input consists of high level commands such as “Retrive block 123”. Its output consists of low level hardware-specific instructions that are use by the hardware controller, which interfaces the I/O device to the rest of the system.