Transcript
DISK ORGANIZATION
OBJECTIVE
To examine the basic formats for hard disk and diskette, storage, the boot record, directory and the file allocation table
CHARACTERISTICS OF A DISK STORAGE DEVICE
Terminologies
• TRACKS - concentric circles on the disk’s surface
• SECTOR - division on each track; size=512 bytes
• CYLINDERS - vertical set of all cylinders
DISK CONTROLLERS
DISK CONTROLLERS
DISK CONTROLLERS
• handles the placement of the R/W heads on the disk surface
Difference bet the Hard Disk & the Floppy Disk Drives
1. Hard Disk - R/W is placed only above the disk
2. The HD device rotates constantly
CYLINDER
• Usually starts from 0• when writing a file, the controller fills all the
tracks on the cylinder before advancing to the next.
• referencing disks:– by Physical Sector: heads, tracks, sector by
number– by Relative Sector: numbered relative to the
start of the disk
DISK CONTROLLER
• located bet. the processor and disk drive
• handles all communication bet. them
• accepts data from the processor and converts the data into a form that is usable by the device
• provides the command for moving the R/W heads
Direct Memory Access (DMA)
• processor provides:– R/W Command– address of the I/O buffer in memory– number of sectors to transfer– numbers of cylinder– head– starting sector
Factors affecting Data Transfer Rate
1.1. Access ( Seek) TimeAccess ( Seek) Time - movement required for the R/W head to reach the required cylinder/track
2.2. LatencyLatency - time it takes for the data to be transferred from the sector to the processor
CLUSTER
• A group of sectors that the system treats as a unit of storage space.
• size is always a power of 2
• Hard Disk– may be divided into more than 1 partition– each partition divided by a drive number– 2 types of FAT, FAT 16, FAT 32 determines
the size of the clusters
CLUSTERS
• FAT 16 (Partition: 128 MB or less - 2,074 MB)
– Min Cluster size = 2 KB; No. of sectors 4– Max = 32 KB, 64 sectors
• FAT 32 (Partition: 260 MB - 32 GB)
– Min Cluster size = 4 KB; No. of sectors 8– Max = 32 KB, 64 sectors
The Disk System Area and the Data Area
• certain sectors are reserved for the purpose of supplying information about the files on the disk
• General Organization of a disk:– system area– data area
SYSTEM AREA
• 1st area, outermost track= side 0, track 0 sector 1
• Three components:1. the boot record
2. the FAT
3. the Directory
BOOT RECORD
FAT DIRECTORYSystem
FilesUser Files
System Area Data Area
SYSTEM AREA
DATA AREA
• for a bootable disks begins with the 2 system files:– MSDOS.SYS– IO.SYS
• User files follow immediately after the system files or if there are no system files begins at the start of the data area
THE BOOT RECORD
• contains the instructions that load system files from disk to memory
• all formatted disks contain a boot record
THE DIRECTORY
• for each file, the system creates a 32-byte directory that describes – the name of the file, – the data of creation, – its size and – the location of its starting address
FILE SYSTEMS• FAT12
– Cluster size is only 512 bytes– ideal for storing small files– holds fewer than 4087 clusters
• FAT16– only available format for hard drives formatted under
MSDOS– inefficient on volumes over 1GB because it uses large
cluster sizes– can hold bet. 4087 - 65,526 clusters– boot sector not backed-up, a single sector read error
can be catastrophic– no built-in file system security or individual user
permission
FILE SYSTEMS• FAT32
– Cluster size is only 512 bytes– ideal for storing small files– holds fewer than 4087 clusters
• FAT16– only available format for hard drives formatted under
MSDOS– inefficient on volumes over 1GB because it uses large
cluster sizes– can hold bet. 4087 - 65,526 clusters– boot sector not backed-up, a single sector read error
can be catastrophic– no built-in file system security or individual user
permission
NTFS
• NTFS (New Technology File System)[1] is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7.[5]
• NTFS supersedes the FAT file system as the preferred file system for Microsoft’s Windows operating systems. NTFS has several improvements over FAT and HPFS (High Performance File System) such as improved support for metadata and the use of advanced data structures to improve performance, reliability, and disk space utilization, plus additional extensions such as security access control lists (ACL) and file system journaling.
-http://en.wikipedia.org/wiki/NTFS
FILE SYSTEMS
NTFS
OS Support for File Systems
Sector Mapping1.44 MB Diskette : FAT 12 and FAT 16 have a fixed location for the boot record but not FAT 32
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