The file system

October 2016

What is a file system?

Even though hard drives can be very small, they still contain millions of bits and therefore need to be organized so that information can be located. This is the purpose of the file system. Remember that a hard drive is made up of several circular platters rotating around an axis. The tracks (concentric areas written to on either side of the platter) are divided into pieces called sectors (each 512 bytes in size). Logical formatting of a disk allows a file system to be created on the disk, which in turn will allow an operating system (DOS, Windows 9x, UNIX, ...) to use the disk space to store and use files. The file system is based on management of clusters, the smallest disk unit that the operating system is able to manage.

A cluster consists of one or more sectors, so the larger the cluster size, the fewer entities the operating system will have to manage…
On the other hand, since an operating system only knows how to manage whole allocation units (i.e. a file occupies a whole number of clusters), the more sectors per cluster, the more wasted space there will be. This is why the choice of file system is important.

Files systems and the operating system

In reality, the choice of file system depends first of all on the operating system that you are using. In general, the more recent the operating system, the greater the number of files it will support. So, under DOS and on the first versions of Windows 95, FAT16 is required.

Starting with Windows 95 OSR2, you have the choice between FAT16 and FAT32 file systems. If the partition size is greater than 2GB, then FAT file systems are excluded and you need to use the FAT32 system (or modify the size of the partition).

Below this limit, FAT16 is recommended for partitions with a capacity of less than 500Mb, otherwise it is preferable to use FAT32.

In the case of Windows NT (up until version 4) you have the choice between the FAT16 system and NTFS, FAT32 is not supported. In general, the NTFS system is recommended as it provides higher security and better performance than the FAT system. Microsoft actually recommends using a small FAT-type partition (of between 250 and 500MB) for the operating system, so as to be able to boot from a bootable DOS floppy disk in case of a catastrophe, and to use a second partition for storing your data.

Under Windows NT5, there is more choice as it accepts FAT16, FAT32 and NTFS partitions. Once again, the more recent file system (NTFS 5) is recommended, as it offers many more features than the FAT systems. For the same reasons given above, you can still choose to have a FAT-type partition.

Operation system File system types supported
Dos FAT16
Windows 95 FAT16
Windows 95 OSR2 FAT16, FAT32
Windows 98 FAT16, FAT32
Windows NT4 FAT, NTFS (version 4)
Windows 2000/XP FAT, FAT16, FAT32, NTFS (versions 4 and 5)
Linux Ext2, Ext3, ReiserFS, Linux Swap(, FAT16, FAT32, NTFS)
MacOS HFS (Hierarchical File System), MFS (Macintosh File System)
OS/2 HPFS (High Performance File System)
FreeBSD, OpenBSD UFS (Unix File System)
Sun Solaris UFS (Unix File System)
IBM AIX JFS (Journaled File System)

Coexistence of several file systems

When several operating systems coexist on the same machine, the problem of choosing a file system is at its worse. Since the file system is tightly coupled to the operating system, when there are several operating systems you must choose a file system for each, bearing in mind that it is possible that data from one operating system may be accessed from another. One solution would be to use FAT partitions for all the systems, making sure that the partitions are no larger than 2 GB. The most appropriate solution would be to use for each OS a partition whose file system is best suited to it, and to use a a dedicated FAT16 partition for data to be shared by the different operating systems.

Related :

El sistema de archivos
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Das Dateisystem
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Le système de fichiers
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Il file system
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O sistema de arquivos
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