File systems and how a file is really stored

Inodes, block pointers, directories as tables, and why deleting a file does not erase it.

12 min read · Lesson 6 of 6 · Pro

A disk knows nothing about files

A disk offers numbered blocks, typically 4096 bytes each. Read block 91,447. Write block 91,448. That is the entire interface. There are no names, no folders, no sizes.

A file system is the data structure that turns that flat array of numbered blocks into files and directories. On Linux that is usually ext4; on Windows NTFS; on a pen drive, FAT32 or exFAT.

The inode holds everything except the name

In Unix file systems, each file has an inode — a fixed-size record holding the file's metadata:

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