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File Systems: FAT, NTFS, and HFS+

File Systems: FAT, NTFS, and HFS+
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  • 0:52 How Data Are Stored
  • 4:08 FAT
  • 5:13 NTFS
  • 6:12 HFS+
  • 6:40 Other Considerations
  • 7:54 Lesson Summary
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Lesson Transcript
Instructor: Paul Zandbergen

Paul has a PhD from the University of British Columbia and has taught Geographic Information Systems, statistics and computer programming for 15 years.

Computers use file systems to control how information is stored and retrieved. Each file system has its own structure and logic. Learn about the different types of file systems for different operating systems in this lesson.

Why File Systems Matter

So you are working in the office and your colleague walks in with an external hard drive. 'Can you copy those files from the project to my drive?' 'Sure.' You plug in the drive, but nothing happens. Why can't you see your colleague's drive? You remember that he is a Mac user, and you are on a Windows-based computer. Could that have something to do with it?

Then, the IT support person walks in and says, 'You are NTFS, and he is HFS+. You should both be FAT.' What language is he talking, and what does this have to do with your weight? Welcome to file systems. Now, it's time to take a closer look at how data storage works.

How Data Are Stored

Let's consider how data are stored on a hard disk drive. There are other types of storage, but hard disk drives are widely used and the general concepts apply to other types.

A disk is broken down into tracks, sectors and clusters. A track represents a concentric circle, while a sector is a like a slice of pie. The intersection of these two results in track sectors. Two or more of these track sectors make up a cluster, sometimes referred to as a block.

A cluster is the minimum unit used by the operating system to store data. The size of each cluster varies with its location on the disk. You might think that each cluster is used to store a file, but that is not exactly how it works.

To learn about how files are stored, think of the storage disk as a bookcase with a number of different shelves. Your files are like books being placed on the shelf. Some books are only a few pages thick, while others are serious door stoppers. You may also have multi-volume books, such as a series or encyclopedia. You start off by placing your books on the shelves in a somewhat organized manner. Your shelves start to fill up, and it is becoming harder to stay organized.

You receive a new trilogy of books that can't fit on just one shelf, and so you have to break it up, putting it onto three different shelves. You start removing books that you no longer need, creating 'holes' in the rows of books - and you can't move any of the books that are already there to a different location; that is one of the rules.

Once your bookshelf is pretty full and after you have been adding and removing books, your books are no longer very organized. That new trilogy that you just received is located in three different places, since there was no other place to put them where they could be together.

What if you now wanted to read that trilogy? How would you find it without having to search through all the shelves? It would have been helpful if you had written down somewhere which shelf each part of the trilogy is on and where on the shelf it is located. What you need is a file system.

Data storage on hard disk drives works in a similar manner, but instead of working with shelves in a bookcase, you use clusters on a disk. Just like a multi-volume book may be located on different shelves, files may be located in different clusters.

A file system is a systematic way to control how information is stored and retrieved. It describes where one piece of information stops and where the next one begins. Each file system has its own structure and logic.

There are a number of different file systems that have been developed over the years for different types of storage devices and for different operating systems. Which file system is used by a particular disk is determined when it is formatted, i.e. when it is first used.

FAT

One of the older types of file systems is the file allocation table, or FAT. FAT is a table that the operating system maintains on a storage device that provides a map of the clusters that contain each file. The actual FAT is located in disk sector 0, which is the first sector.

Different versions of FAT have been developed, including FAT12, FAT16, FAT32, etc. The number refers to the number of bits being read at the same time. FAT was originally developed for the MS-DOS operating system and later for Windows, but today, it is supported by most operating systems. FAT is no longer the preferred file system for any particular computer system, but it remains widely used for storage on multiple operating systems. One of the limitations of FAT is that the most recent FAT32 version only supports a maximum file size of 4 GB.

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