Disk Organization 1

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