File Systems


Physically, the hard disks and other media provide the basic technology for storing data. Logically, however, the file system provides the structure of volumes and folders in which you store individual files and the organizational model that enables the system to locate data anywhere on a given disk or drive. File systems typically are an integrated part of an operating system (OS), and in general the newer versions of Windows provide support for several file systems from which you can choose.

Normally a file system is chosen for a volume when that volume is created or formatted. In some cases there are utility programs that can change a file system from one type to another on an existing partition. Depending on the version(s) of Windows you are running, several file systems are available from which to choose. Each file system has specific limitations, advantages, and disadvantages, and which ones you use can also be limited by the operating system you choose.

The primary file systems to choose from today include

  • File allocation table (FAT), which includes FAT12, FAT16, and FAT32

  • New Technology File System (NTFS)

Note that only Windows 2000/XP and later support all of these file systems; older or less capable versions of Windows generally support only some of these file systems. Table 10.19 lists the file systems supported by various Microsoft operating systems including various versions of DOS and Windows.

Table 10.19. Microsoft OS File Systems Support

Operating System

FAT12

FAT16

FAT32

NTFS

MS-DOS 1.x2.x

X

     

MS-DOS 3.x6.x

X

X

   

MS-DOS 7.x8.x

X

X

X

 

Windows 3.1

X

X

   

Windows 95

X

X

   

Windows 95B

X

X

X

 

Windows 98/98SE

X

X

X

 

Windows Me

X

X

X

 

Windows NT

X

X

 

X

Windows 2000

X

X

X

X

Windows XP

X

X

X

X


Although other operating systems may support other file systems, such as the Ext2FS supported by Linux or the HPFS (High Performance File System) supported by OS/2, this chapter focuses on the FAT and NTFS systems as supported by Windows.

Clusters (Allocation Units)

File systems store data in clusters, which are often called allocation units . The term allocation unit is appropriate because a single cluster is the smallest unit of the disk that the operating system can handle when it writes or reads a file. A cluster is equal to one or more 512-byte sectors, in powers of 2. Although a cluster can be a single disk sector, it is usually more than one. Having more than one sector per cluster reduces the size and processing overhead and enables the operating system to run faster because it has fewer individual units to manage. The trade-off is in wasted disk space. Because operating systems manage space only in full-cluster units, every file consumes space on the disk in increments of one cluster.

Because the operating system can allocate only whole clusters, inevitably a certain amount of wasted storage space results. File sizes rarely fall on cluster boundaries, so the last cluster allocated to a particular file is rarely filled completely. The extra space left over between the actual end of the file and the end of the cluster is called slack . A partition with large clusters has more slack space, whereas smaller clusters generate less slack.

The effect of larger cluster sizes on disk utilization can be substantial. A 2GiB partition containing about 5,000 files, with average slack of one-half of the last 32KiB cluster used for each file, wastes more than 78MiB (5000x(.5x32)KiB) of file space. When files under 32KiB in size are stored on a drive with a 32KiB allocation unit, waste (slack) factors can approach 40% of the drive's capacity. Newer file systems such as FAT32 and NTFS allow the use of smaller clusters, which use space on the disk more efficiently . For example, the same 2GiB partition with 5,000 files on it mentioned earlier would use 4KiB clusters with either NTFS or FAT32 instead of the 32KiB clusters used with FAT16. Assuming the same amount of slack for each file, the smaller cluster size reduces the average amount of wasted space on that partition from more than 78MiB to less than 10MiB.

Note

How much space does your current cluster size waste? To find out, you can download a free Windows utility called Karen's Disk Slack Checker from Karen Kenworthy's website. Go to http://www.karenware.com/powertools/ptslack.asp.





Upgrading and Repairing Microsoft Windows
Upgrading and Repairing Microsoft Windows (2nd Edition)
ISBN: 0789736950
EAN: 2147483647
Year: 2005
Pages: 128

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net