Windows XP File Systems Tutorial 3

File System “File system” refers to the data structures that an operating system uses to track information on files stored on a disk. Windows XP supports three file systems: FAT (for FAT 16) FAT32 NTFS

FAT16 File System Original version of Windows 95 and 95a used FAT for backward compatibility with DOS. Relied on the use of a File Allocation Table (FAT).

FAT16 File System Operating systems that use the FAT file system perform three operations when formatting a floppy disk. Subdivides disk into storage compartments—tracks and sectors. 80 concentric tracks on a 3 ½-inch high-density floppy; each track 18 sectors Data stored on a cluster basis Cluster—allocation unit of one or more sectors of storage space that is used when storing a file # of sectors/cluster varies depending upon the type of disk and file system—see Figure 3-7, pg. 3.11

Checks disk surface for defective sectors The same file could use from one to 64 sectors of storage space depending upon the type of file system FAT16 supports only hard disks up to 2 GB in storage space Checks disk surface for defective sectors If it has a problem reading from or writing to a sector, it marks the cluster and doesn’t store there Creates four tables in the system area (outer area) of the disk Boot record File Allocation Table #1 (FAT1) File Allocation Table #2 (FAT2) Directory table

Boot Record (boot sector) is a table containing the name and version number of the operating system used to format the floppy disk and information on the physical characteristics of the disk Number of bytes per sector Number of sectors per cluster Number of FATs Number of files allowed in the top-level folder or root directory Number of sides formatted Drive number Type of file system

Boot sector contains the names of the operating system files needed to start the process of loading the OS, as well as the bootstrap loader program which locates and loads the OS if the floppy disk is a boot disk. If the floppy does not contain the OS files and is left in drive A, you get an “Invalid system disk” error. The system must read the boot sector when accessing a floppy disk so it knows how to work with and allocate storage space on that disk drive.

File Allocation Table—The OS creates two copies of the FAT to keep track of which allocation units (or clusters) are available or unused and which contain data, which are defective and unusable, and which are reserved for the OS. See Figure 3-8, pg. 3.12 Two copies of the FAT are maintained (security). Directory Table keeps track of information on folders and files stored in the top-level folder or root directory. Contains names of folders and files and information on their sizes, dates/creation times, last access date and modification, and special attributes Only includes folders and files in top-level folder. Each subfolder below the top level is actually a directory table.

How is directory space limited? Attributes R Read-Only Io.sys Msdos.sys H Hidden Boot.ini Hiberfil.sys (stores contents of RAM on disk when the computer switches to Hibernation mode S System A Archive Newly created or modified files so that a backup utility can identify which files should be backed up D Directory Folders The directory table also contains the number of the starting cluster for each folder and file. By using the directory table and FAT the OS can locate all the clusters used by a folder or file and reassemble the file How is directory space limited?

Master Boot Record and Hard Disk Partition Table Each drive on a hard disk that uses the FAT file system has a boot record, two copies of the FAT, and a directory table. However, the first sector on a hard disk is not the boot sector for drive C but rather the Master Book Record (MBR). The boot sector for drive C follows the Master Boot Record. The MBR contains information on the hard disk’s partitions—all or part of the physical hard disk that is set aside for a drive or set of logical drives. Primary partition is the bootable partition that contains the OS (usually drive C) Extended partition does not contain OS files but can be divided into additional logical drives, such as drive D, etc. Can have as many as 23 logical drives (D-Z)

Windows XP supports FAT16 Within the MBR is a table called the Hard Disk Partition Table that contains info about the partitions on the hard disk, such as the amount of storage space Windows XP supports FAT16 Provides backward compatibility with earlier versions of Windows and thereby enable you to upgrade your OS. Another advantage of providing support for FAT16 is that it is compatible with most other operating systems. In a multiboot configuration with MS-DOS, Windows 95 (original version), or Windows 95b, you must use FAT16 for the partition from which one of these operating systems boots. On the Windows XP partition, you can use its native file system, NTFS; however, the contents of the XP partition can’t be read by a partition running MS-DOS, Windows 95, Windows 98, Windows Me, or Windows NT Workstation 4.0.

FAT32 File System Windows XP, Windows 2000, Windows Me, Windows 98, Windows 95b, and Windows 95c support FAT32 FAT 32 improves the efficiency of storage space use Hard disks with storage capacities from 257 MB to 8 GB have cluster sizes of 8 sectors (a 2 GB hard drive using FAT 32 has cluster sizes of 8 sectors compared to 64 sectors with FAT16– issue of slack) Support drives up to 8 TB theoretically, yet FAT 32 volumes are limited to 32 GB because Windows XP can only format volumes up to 32 GB; above that use the NTFS file system Microsoft says FAT32 is 10 to 15 percent of efficient in using disk space than FAT16 and improves use of storage space on large drives; also claims applications load 50 percent faster

NT File System (NTFS) Windows XP has its own native file system, the NT File System. When installing XP, you can choose a file system and specify a file system when you format a volume. XP can convert a FAT16 or FAT32 volume to an NTFS volume without formatting the volume. XP can upgrade previous versions of NTFS to the version used in Windows XP

NTFS does not use a File Allocation Table with pointers; relies on a Master File Table (MFT), a special file that keeps information about the folders and files on disk as well as the volume itself. The MFT contains a transaction log of disk operations so files can be recovered if disk problems occur and even repair itself. Attributes—in addition to System, Hidden, Read-Only, and Archive attributes, support three addition ones Compress Encrypt Index

Compress Attribute Compression operates transparently when compression is enabled; use of folder or file does not change XP displays compressed folders and files in a different color from uncompressed ones A compressed file cannot be encrypted You can only apply the Compress attribute to the contents of an NTSF volume Windows XP now supports a feature called Compressed (zipped) Folders that works on FAT and NTFS volumes. Any files you place in a compressed (zipped) folder are compressed; you can move these folders on any drive or folder on the local or network computer or Internet. Operates as a .zip file; if sent to computer without the feature, open with package like PKZIP.

Encrypt Attribute Index Attribute Prevents access to a folder or file by any person other than the user who encrypted the folder or file or the system administrator Use of folder/file does not change; encryption handled transparently. Index Attribute Indexes contents of a file and its properties so that you can search for text within a file as well as search for file properties

FS Comparisons NTFS uses disk space more efficiently than either FAT16 or FAT32 Clusters for volumes from 2 GB up to 2 TB are only 8 sectors in size (see Figure 3-16, pg. 3.20 Superiority of NTFS Supports larger volume sizes Uses storage space more efficiently Provides enhanced security