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A local file system is a structured environment established on a hard drive to enable it to store files
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Computers see data as nothing but 0s and 1s A blank hard drive is a giant sea of 0s, ready to have 1s strategically placed like buoys in a busy harbor But how should the computer organize the data on the hard drive That s a tricky question Every operating system deals with this question in a different way These organizational strategies are called file systems The most common file systems have names like FAT16, FAT32, NTFS, JFS, FFS, UFS, VFS, and ext2/3 Early file systems were just responsible for getting information on and off a storage device The operating systems were responsible for controlling the way in which the information was used More recent systems have direct support for access control, error recovery, and data security The majority of users and organizations today employ two basic types of operating systems, Unix or Windows For this reason, the file systems used by these operating systems are covered in the greatest depth
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One of the earliest Microsoft file systems was called (File Allocation Table 16 [FAT16]) It integrated with an operating system called Disk Operating System (DOS) It worked by breaking the hard drive up into regions Each region was given an address, which was a number between 0 and 65,535 (this is 2 to the 16th power, thus the 16 part of FAT16) When a file is stored, the data starts at the beginning of a region If the file is larger than the region, it keeps flowing into additional regions A lookup table links the filename with the starting addresses of each region used Any unused space in a region is lost These address regions are often referred to as clusters or blocks The size of the address region has an impact on the overall efficiency of a file system At a basic level, the number of total addresses multiplied by the region size can t be smaller than the drive; otherwise the remaining space is wasted For example, on a 2-gigabyte drive formatted with FAT16 each address region needs to be 32 kilobytes This is ok when storing a small number of large files However, when saving many small files a large amount of space is going to be wasted, possibly more than a gigabyte This space is wasted because no matter how small the data actually is, it will take up 32 kilobytes worth of space This problem prompted Microsoft to increase the address range of their file system and resulted in FAT32 (released with Win98) Under FAT32, over 4 million addresses are possible This allows very large hard drives to use relatively small region sizes, which can minimize wasted space to under 10 percent Why not use even more addresses The larger the address space, the longer it takes to find and retrieve files on the storage system The goal is to strike a balance between the performance and efficiency of space allocation In between FAT16 and FAT32, Microsoft developed a next-generation file system to go with their New Technology (NT) line of server operating systems In an unparalleled burst of creativity, they called it NTFS We ll let you figure out the acronym NTFS was their first file system that provided more than basic load/save functionality It interacts with the operating system to provide users with file and directory access control This means that users can protect their information from other users, or choose to share information with a limited selection of users NTFS also prevents users from directly undeleting information removed from the file system Most importantly, NTFS implements systems for improving the reliability of the storage process It is very difficult for an application to write data to NTFS in a way that results in a corrupted file or directory, even if the application or operating system crashes midway through the process The system automatically will attempt to repair any errors in the background, another useful benefit With all those features, NTFS is still not very secure If the hard drive is accessed from another operating system, all the data becomes available without security restrictions This is relatively easy to do with the right bootable floppy disk As a result, Microsoft created an enhanced version of NTFS for their Windows 2000 operating systems The enhancements focused on security improvements and
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Part VIII Storing Information 265 scalability Security was improved by implementing direct support for encrypting the entire file system and all user files This would prevent the bootdisk attack 23 described above Scalability was improved by moving to a 64-bit address table, en- Storing abling up to 18,000,000,000,000,000,000 possible drive region addresses We had to Information: Local File print out the number because we just don t know the name for something that big Systems While this was going on, the Unix world was busy creating its own file systems Two fundamental differences between the Unix world and the Windows world were apparent First, Unix was designed as a multiuser environment from the beginning This meant that user-level security was an early concern This led to an early adoption of security and reliability features only found in the more recent versions of NTFS Second, many different vendors were creating competing versions of Unix As a result, a number of different and incompatible file systems were in use The result was the Virtual File System (VFS), a generic approach to dealing with arbitrary file systems The VFS is a powerful concept As far as the operating system is concerned, only one type of file system is available This means that the development of file system code can be totally separated from the development of the operating system Any data source that provides the right access commands can be treated as a VFS For example, in many Unix systems, the kernel (main processing code) can appear as a file system No actual files exist instead, various kernel code and parameters can be viewed and modified in a directory structure Thanks to the Virtual File System, it is easy to access foreign file systems (many Unix systems can read NTFS and FAT16/32 systems with ease) It s also possible to create network-level file systems These systems don t interact directly with storage devices, but treat the entire local file system as a storage device Network File System (NFS) and Andrew File System (AFS) are two examples of file systems designed to operate over a network, which we ll discuss later in this chapter The most current Unix-world file systems support fault tolerance and prevention, as well as the automatic recovery of information These systems are known as journaling file systems Also, certain file systems are capable of providing file system and user-file encryption At the moment, both Unix and Windows systems are fairly equal when considering the potential security level of the file system
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