In Memory Data Structure

Till now, we have discussed the data structures that are required to be present on the hard disk in order to implement file systems. Here, we will discuss the data structures required to be present in memory in order to implement the file system.

The in-memory data structures are used for file system management as well as performance improvement via caching. This information is loaded on the mount time and discarded on ejection.

1. In-memory Mount Table

In-memory mount table contains the list of all the devices which are being mounted to the system. Whenever the connection is maintained to a device, its entry will be done in the mount table.

2. In-memory Directory structure cache

This is the list of directory which is recently accessed by the CPU. The directories present in the list can also be accessed in the near future so it will be better to store them temporally in cache.

3. System-wide open file table

This is the list of all the open files in the system at a particular time. Whenever the user open any file for reading or writing, the entry will be made in this open file table.

4. Per process Open file table

It is the list of open files subjected to every process. Since there is already a list which is there for every open file in the system thereforeIt only contains Pointers to the appropriate entry in the system wide table.