Hard disk drives It is a non volatile mass storage device. It consists of platters made of aluminum alloy or glass ceramic composite material. Platters are coated with magnetic material on both sides and stacked one on top of another. Platters are divided into concentric rings called tracks. Tracks are divided into sectors. Each sector contains 512 bytes of data. Each track is a part of a cylinder which consists of all the tracks in the same position on each platter surface.

Smallest unit of storage on a hard disk is cluster. The size of a cluster depends on 2 factors. 1.)Size of the partition 2.)file system associated with the partition. Clusters are also called allocation units. Cylinder skewing Difficulty in catching the 1 st sector of next track during same rotation. When the cylinders are skewed, the first sector of each track is offset from that of the next track by one sector.

Zoned bit recording It is a technique that varies the number of sectors on each track. Cylinders are split into a number of zones. Each of the tracks in a particular zone has the same number of sectors. Outer zones have more sectors than inner zones.

IDE Interface Stands for Integrated Drive Electronics,i.e controller is integrated on to the drive not as a separate unit. Advantages 1.)communication between controller and drive is efficient. 2.)communication need not have to be standardized. The original name for interface for hard drives is AT Attachment(ATA).

ATA standards come in different versions;ATA1,ATA2,ATA3,ATA4,ATA5,ATA6 ATA 1 Supports two hard disks. Supports PIO modes 0,1,2. Supports single word DMA mode0,1,2 and multiword DMA mode 0. Data transfer rate is 8.3 Mb/s. Supports 528 MB ATA 2 Supports PIO modes 3and 4. Supports multiword DMA modes 1,2.

Introduces power management functions,block mode transfers and logical block addressing. It has an Identify Drive instruction. Seagate named it as Fast ATA,Western Digital named it as EIDE. ATA 3 Improved reliability Has Self Monitoring Analysis and Reporting Technology(SMART) Has security mode which allows devices to be protected with a password. Supports Ultra DMA modes 0,1,2.

Has CRC(Cyclic Redundancy Check). ATA 4 Supports ultra DMA modes 0,1 &2. Introduced 80 pin connector(optional) ATA 5 Supports ultra DMA modes 3,4. Introduced 80 pin connector(mandatory) ATA 6 Under development

Data Transfer Modes Programmed Input/output(PIO) Direct Memory Access(DMA) Ultra DMA

PIO mode Oldest mode of transferring data in IDE interfaces. PIO modeTransfer Rate(MB/sec) Data cycle time(ns) Supporting standards All All All ATA 2,FAST ATA,FAST ATA2,ATA 3,ATAPI ATA 2,FAST ATA2,ATA3,ATAPI

Single Word DMA mode Single word DMA modeTransfer Rate(MB/sec)

Multiword DMA mode DMA modeTransfer rate(MB/sec) Data cycle time(ns)Supporting Standards All ATA2,FAST ATA2,ATA ATA2,FAST ATA2,ATA3

ULTRA DMA MODES Ultra DMA modeTransfer rate(MB/sec) Data cycle time(ns)Supporting Standards ATA 4,ATA 5,ATA ATA 4,ATA 5,ATA ATA 4,ATA 5,ATA ATA 5,ATA ATA 5,ATA ATA6

Standard CHS addressing 528MB limitation. ATA used to build drives and BIOS int 13h used to access them devote a specific no: of bits for each cylinder ref:,head ref:,sector ref:. StandardCylinder bitsHead bitsSector bitsTotal bits ATA BIOS INT13h108624

StandardMax CylindersMax HeadsMax SectorsMax Capacity ATA65, GB BIOS int 13h GB

Extended CHS Addressing To get around 528MB drive size limitation. StandardCylinderHeadSectorTotal Bits104620bits NO: of units MB

ECHS Bios divides tha no: of cylinders by an integer that will result in a number less than 1024 and then multiplies no: of heads by the same integer. For eg:,a drive with 6304 cylinders,16 heads,63 sectors.

To get a number of cylinders below 1024,BIOS divides the number of cylinders by 8 to get 787,and multiplies the number of heads by 8 to get 128 and the no: of sectors remain at 63. At the end we get a drive of 3.25GB within the limitations of both ATA and BIOS int 13h standard.

Logical block addressing Now a days for drive addressing we use LBA. We assign a unique identifier to each sector on a hard drive. Sectors are numbered starting from 0. Internally the no: is a 128 bit binary which is translated to corresponding decimal no:. Compared to ECHS addressing,it is simpler.

Disk formatting It is a process of preparing hard disk for use. Two types of formatting 1.low level 2.high level In Low level formatting all the cylinders, tracks and sectors of the disk are outlined. When you buy a hard drive, it has already undergone low-level formatting. SO YOU DO NOT NEED TO PERFORM LOW-LEVEL FORMATTING.

Partitioning drives Drive can have 1 to 24 logical drives. Logical drives can be obtained by partitioning physical drive. Reasons for partitioning are: 1.there must be at least one master boot partition on the drive in order to high level format the drive. 2.to install more than one OS and keep them on separate logical drives. 3.to install different file systems. 4.To keep other applications separate from OS.

High level formatting Different file systems used are FAT16,VFAT,FAT32,NTFS etc. File systems are tables that an OS uses to locate files on the disk. It creates a file system on the disks that allow an OS to use the disk space to store and access files.

NTFS Originally built for Windows NT. Comes in two versions:NTFS 1.1 & NTFS 5.0 Features Reliability Security and access control Breaking size barriers Storage efficiency Long file names