FlLE SYSTEMS

The UNIX V7 File System
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The UNIX V7 File System

The early versions of UNIX had a fairly sophisticated multiuser file system since it was derived from MULTICS. Below we will talk about the V7 file system, the one for the PDP-11 that made UNIX famous. The file system is in the form of a tree starting at the root directory, with the

The MS-DOS File System
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The MS-DOS File System

The MS-DOS file system is the one the first IBM PCs came with. It was the main file system up through Windows 98 and Windows ME. It is still supported on Windows 2000, Windows XP, and Windows Vista, although it is no longer standard on new PCs now except for floppy disks.

EXAMPLE FILE SYSTEMS
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EXAMPLE FILE SYSTEMS

In the next sections we will discuss numerous example file systems, ranging from quite simple to more sophisticated. Since modern UNIX file systems and Windows Vista's native file system are covered in "UNIX" and "Windows Vista" we will not cover those systems here. We will,

Defragmenting Disks
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Defragmenting Disks

When the operating system is at first installed, the programs and files it requires are installed consecutively starting at the beginning of the disk, each one directly following the previous one. All free disk space is in a single contiguous unit following the installed files. On the other

File System Performance
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File System Performance

Access to disk is much slower than access to memory. Reading a 32-bit memory word might take 10 nsec. Reading from a hard disk might proceed at 100 MB/sec, which is four times slower per 32-bit word, but to this must be added 5-10 msec to seek to the track and then wait for

File System Consistency
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File System Consistency

Another area where reliability is an issue is file system consistency. Many file systems read blocks, modify them, and write them out later. If the system crashes before all the modified blocks have been written out, the file system can be left in an inconsistent state. This problem is

File System Backups
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File System Backups

Destruction of a file system is sometimes a far greater tragedy than destruction of a computer. If a computer is destroyed by fire, lightning surges, or a cup of coffee poured onto the keyboard, it is annoying and will cost money, but usually a replacement can be purchased with a

FILE SYSTEM MANAGEMENT AND OPTIMIZATION
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FILE SYSTEM MANAGEMENT AND OPTIMIZATION

Making the file system work is one thing; making it work efficiently and robustly in real life is another thing. In the following sections we will examine some of the issues involved in managing disks.

Virtual File Systems
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Virtual File Systems

Several different file systems are in use - often on the same computer - even for the same operating system. A Windows system may have a main NTFS file system, but also a legacy FAT-32 or FAT-16 drive or partition that includes old, but still needed, data and occasionally a

Journaling File Systems
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Journaling File Systems

While log-structured file systems are an interesting idea, they are not extensively used, in part due to their being highly incompatible with existing file systems. However, one of the ideas inherent in them, robustness in the face of failure, can be easily applied to more conventional

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