In Unix systems, what is the difference between the main memory index node and the secondary index node in terms of content, why set the main memory index node?

Main Memory index node and secondary index node are mainly reflected in: Memory index node State; Device number, index node number; reference count.

Main Memory Index node state-reflects the use of main memory index nodes. It indicates the following:

1, whether the index node is locked;

2. Whether there is a process waiting for the index node to become unlocked state

3, as a result of changes to the data in the index node, the main memory of the index node indicates whether it is different from the contents of its disk.

4. As a result of changes to the file data, the main memory of the file indicates whether it is different from the contents of its disk.

5, whether the file is the installation point.

Device number, index node number. Corresponds to the location information of the secondary index node. The device number is the index node and the device number of the device on which the file resides, and the index node is the number of the index node in the Secondary index node area.

The reference count. Indicates the count of active references to the file.

(The file owner identification number, file type, and other items are the same as the contents of the secondary I node.) ）

In order to improve the system efficiency, reduce the main memory space occupied.

In Unix systems, what is the difference between the main memory index node and the secondary index node in terms of content, why set the main memory index node?