4 lessons
What a file actually is, and how directories find them
The OS's most user-facing abstraction, broken down to what it really is underneath — just organized bytes plus a lot of bookkeeping.
File allocation methods — where a file's actual bytes live on disk
Three different strategies for tracking which disk blocks belong to which file, and the very familiar fragmentation trade-offs that reappear here too.
Tracking free space, and surviving a sudden power loss
How the file system knows which blocks are actually free, and the clever logging trick that keeps your files intact even if the power dies mid-write.
Putting it all together — the full journey of writing a file
A single, concrete walk through everything this entire course covered, following one file write from your keyboard down to the physical disk platter.