9: Implementing Hard Drives in Software

Draw PDF-417 2d barcode in Software 9: Implementing Hard Drives

Most operating systems will allow you to create partitions during the installation process To create partitions at other times, you use a partitioning tool dedicated to that task Older versions of Windows shipped with the command-line program FDISK (fdiskexe) for this purpose Windows 2000 and later versions ship with a graphical tool called Disk Management to manage partitions, convert basic disks to dynamic disks, and manage volumes Linux uses several partitioning tools such as FDISK (same name, but different from the Windows version) and GParted

Since FAT16, a cluster rather than a sector is the basic unit of storage Unlike sectors, the size of a cluster is not fixed; it changes with the size of the partition Because FAT16 still supported only a maximum of 64-K storage units, the formatting program set the number of sectors in each cluster according to the size of the partition After the format program creates the FAT, it tests each sector and places a special status code (FFF7) in the FAT for any bad sectors so they won t be used Good sectors are marked with 0000 When an application saves a file, the OS starts writing the file to the first available cluster marked as good If the entire file fits in the cluster, the OS places the end-of-file marker (FFFF) in the cluster s status area If the file does not fit entirely in a single cluster, the OS searches for the next available cluster Once found, the location of this next available cluster is written to the status area of the preceding cluster holding a piece of the file, and the OS writes the next 512 bytes of the file in the available cluster This continues until the file has been completely written and the final cluster in the chain receives the status code FFFF in the FAT After saving the entire file, the OS lists the filename and starting cluster in the file s folder As a file is split across multiple non-contiguous clusters, the file becomes fragmented Fragmentation slows read/write access as the OS has to piece together the many fragments of the file Every version of Windows, except NT, comes with a disk defragmenter program that reorganized the clusters of hard drive data so files are stored wherever possible in contiguous clusters FAT32 was introduced with Windows 95 OS2 FAT32, which uses 32 bits to describe each cluster, supports partitions up to 2 terabytes FAT32 creates smaller clusters and therefore stores files more efficiently than FAT16 The New Technology File System (NTFS) was introduced with Windows NT and has gone through several versions The most recent version, used since Windows 2000, is referred to as NTFS 5 NTFS does not use a FAT like FAT16 or FAT32, but instead uses a master file table (MFT)

After a disk has been partitioned, it must be formatted before it can be used Formatting creates a file system and the root directory You can use the Windows command-line program FORMAT (formatcom) or the GUI tool Disk Management to format a partition or volume Current versions of Windows support three file systems: FAT16, FAT32, and NTFS The base storage area for hard drives is a sector, which can store up to 512 bytes of data If a file is smaller than 512 bytes and does not fill a sector, the rest of the sector remains unused as only one file can reside in any one sector If a file is more than 512 bytes, the file is split into pieces with each piece residing in different sectors If the sectors containing all the pieces of a single file are not contiguous, the file is said to be fragmented MS-DOS version 21 first supported the file allocation table (FAT) The FAT is a data structure similar to a two-column spreadsheet that tracks where data is stored on a hard drive FAT comes in several variations: FAT12, FAT16, and FAT32 The number indicates how many bits are available in the left side of the FAT spreadsheet Floppy disks use FAT12 while hard drives can use FAT16 or FAT32 Every version of Windows fully supports FAT16 FAT16 uses only 16 bits to address sector locations This translates to 216, or 64 K locations With 64 K locations of 512-byte sectors, 64 K 512 bytes hits the ceiling at 32 MB For this reason, FAT16 partitions were initially limited to 32 MB FAT16 later added a feature called clustering that treats a set of contiguous sectors as a single FAT unit

Mike Meyers CompTIA A+ Guide: Essentials (Exam 220-601)

NTFS offers several major improvements over FAT, including redundancy, security, compression, encryption, disk quotas, and cluster sizing A backup copy of the most critical parts of the MFT is stored in the middle of the disk, where it is less likely to become damaged With NTFS, individual files and folders can be protected by allowing only certain users or groups access to them Individual files or folders can be compressed to save hard drive space Files or folders can be encrypted so that they are unreadable to anyone but you Users can be limited to the amount of disk space they use by enforcing disk quotas Finally, cluster sizes can be adjusted to allow support of partitions up to 16 exabytes

initialization process places information on the drive identifying it as part of a particular system New drives are always initialized as basic disks but can be converted to dynamic disks by right-clicking and choosing Convert To Dynamic Disk Creating a partition or volume is just as simple Right-click the drive and choose Create Partition or New Volume Remember that you must create logical drives inside an extended partition before you can format and use it to store files

Once a disk has been initialized and partitioned, you can format it Microsoft requires using NTFS for any partition larger than 32 GB Performing a Quick Format skips the checking of clusters, which results in a faster format but is risky The Windows installation program creates a tiny partition on the C: drive, which is used to later convert the disk to a dynamic disk While you can format and use that space for file storage, it is recommended that you leave it as is A mount point is a folder on an NTFS drive that provides access to another drive that may or may not have a drive letter This allows the new drive to extend the capacity of the drive providing the folder mount point All files in the mount point folder, while looking like they are stored on the first drive, are actually stored on the additional drive Create a mount point by first creating a folder on an NTFS drive Then, launch Disk Management, select the additional partition/ volume, right-click, and choose Change Drive Letter and Paths From there, choose Add and browse to the mount point folder you created earlier You can format any partition/volume in My Computer by right-clicking and choosing Format Alternatively, you can format partitions/volumes from the Disk Management tool Both methods offer you options to perform a Quick Format and enable compression