HARDDISK DRIVE

This  is the secondary storage medium.  This comes in different size and capacity.

Size

 5 ¼” (Desktop HDD)

3 ½” (Laptop HDD)

Capacity

2GB, 4GB, 17GB, 20GB, 40GB, 80GB, 120GB, 160GB, 200GB etc. 

 

Parts of HDD

1. Disk Platter
2. Read / Write Head
3. Head arm
4. Head Actuator Mechanism
5. Spindle Motor
6. Logic Baord
7. Air Filter
8. Bezel
9. Cable and connector

Cylinder

• Combination of tracks through all platters

• A single movement of the read/write head arms can read all the platters of data

Disk Platter

This platter is made up of aluminum or glass ceramic material (Memcore) and

coated with magnetic oxide in which data is stored in the form of  its,depending upon the capacity of the disk the number of platter increases or decreases.

Spindle Motor

In this motor where hard disk is placed and the speed of this motor is the entire hard disk speed.The hard desktop disk runs at a speed of 7200rpm and laptop hard disk rotates at a speed of 12000rpm

Stepper Motor

This motor is the important cause for the movement of the read/write head,the movement of this motor which make the head to move track by track on the platter.This motor is fixed on the above of this motor the platter is fixed.

IDE interface

Hard Drive Operation

Voice Coil Mechanism

The voice coil actuators used in virtually in all hard disk today, this uses a feed back signal from the drive to accurately determine the head position and adjust them. There is an important difference between the stepper motor and voice coil method is moving the heads on the tracks. In the first case, the motion is in steps, with the size of its gear arrangement .The heads can be positioned to any cylinder just by passing an  appropriately varying current through the voice coil for exactly the ight amount of time. To make sure that the current is supplied in the exactly the right way, the control circuitry uses a negative feedback also called as servo feedback.

Write Precompensation

The hard disk drive spins at a constant rate.This known as constant angular velocity. Although constant rotation needs a very simple motor circuit. Tracks closer to the spindle are physically shorter than the tracks towadrs the platter’s edge. Shorter tracks result in the shorter sectors. For inner sectors to hold the same amount of data as outer sctors, data must be packed more densly on the inner sector each magnetic flux reversal is close together. Unfortunately, samller flux reversal produce weaker magnetic fields in the R/W heads during reading.If the inner field is written with a stronger magnetic field,flux transition stored in the media will be stronger. The use of increased writing current to compensate for diminished disk response is known as WRITE PRECOMPENSATION.

Landing Zone

The R/W heads of a hard drive fly within the microinchesof their respective platter surface-held aloft with air currents produced by the spnning platters.When the plater is turned off,however the platter slow to a halt.During this spindown period air flow falls rapidly and heads can liteally “crash” into the platter surface.Whenever the head touches a platter surface the data can be destroyed.Even during normal operation,a sudden shock or dump can cause one or more heads to skid across their surface.Although a drive can be reformatted after a head crash ,data and programes would have to be reloaded from scratch .To avoid head crash during normal spin down, a cylinder is reversed as a landing zone .No data is stored in the landing zone so any surface problem caused by the head landing is harmless.Virtually all hard disk drive automatially move the head assembly over the landing zone before spindown,then gently

lock the heads into place until power is restored.

HDD interfaces

HDD Jumper settings

Formatting

Proper setup and formatting are critical to a drive's performance and reliability
The three major steps in the formatting process for a hard disk drive subsystem are as follows:

•Low-level formatting

•Partitioning

•High-level formatting

Low-Level Formatting

All new hard disk drives are low-level formatted by the manufacturer, and you do not have to perform another LLF before you install the drive.Many people say, for example, that you can't perform a low-level format on an ATA drive, and that if you do, you will destroy the drive. This statement is untrue! What can happen with some of the earliest ATA drives is that you might lose the optimal head and cylinder skew factors that were set by the manufacturer for the drive, as well as the map of drive defects. This can have a negative effect on the drive's performance, but you can still reliably use the drive

Drive Partitioning

Partitioning a hard disk is the act of defining areas of the disk for an operating system to use as a volume.

When you partition a disk, the partitioning software writes a master partition boot sector at Cylinder 0, Head 0, Sector 1the first sector on the hard disk. This sector contains data that describes the partitions by their starting and ending cylinder, head, and sector locations. The partition table also indicates to the ROM BIOS which of the partitions is bootable and, therefore, where to look for an operating system to load

The FDISK program is the accepted standard for partitioning hard disk drives for use with all operating systems up through Windows Me. Windows 2000 and XP use a similar command-line program called DISKPART, or you can partition and format hard disks with the Disk Management

With any version of Windowsas with MS-DOS FDISK or other disk preparation tools enable you to create two types of disk partitions: primary and extended. A primary partition can be bootable but an extended partition can't. If you have only a single hard disk in your system, at least part of the drive must be prepared as a primary partition if you want to start your computer from the hard disk

A primary partition is seen as a single volume or drive letter (C: on one-drive systems), whereas an extended partition acts as a sort of logical container for additional volumes (drive letters D: and beyond). A single extended partition can contain a single volume (also referred to by FDISK as a logical DOS drive) or several volumes (logical DOS drives) of various sizes

Another reason for subdividing a single drive into multiple volumes is increased data security. For example, PowerQuest (the creator of PartitionMagic) suggests a three-volume partitioning scheme that looks like this:

•C: for the operating system and utilities

•D: for applications

•E: and above for data

High-Level (Operating System) Formatting

The final step in the installation of a hard disk drive is the high-level format. Similar to the partitioning process, the high-level format is specific to the file system you've chosen to use on the drive. On Windows 9x and DOS systems, the primary function of the high-level format is to create a FAT and a directory system on the disk so the operating system can manage files

The FAT high-level format program performs the following functions and procedures

:-

•1. Scans the disk (read-only) for tracks and sectors marked as bad during the LLF, and notes these tracks as being unreadable.

•2. Returns the drive heads to the first cylinder of the partition, and at that cylinder (Head 1, Sector 1) writes a DOS volume boot sector.

•3. Writes a FAT at Head 1, Sector 2. Immediately after this FAT, it writes a second copy of the FAT. These FATs are essentially blank except for bad-cluster marks noting areas of the disk that were found to be unreadable during the marked-defect scan.

•4.Writes a blank root directory.

•5. If the /S parameter is specified, copies the system files, IO.SYS and MSDOS.SYS (or IBMBIO.COM and IBMDOS.COM, depending on which DOS you run), and COMMAND.COM to the disk (in that order).

•6. If the /V parameter is specified, prompts the user for a volume label, which is written as the fourth file entry in the root directory.

Now, the operating system can use the disk for storing and retrieving files, and the disk is a bootable disk.

IDE STANDARS

(Integrated Drive Electronics)

There have been four main types of IDE interface based on three base standards:-

1. Serial AT Attachment (ATA)
2. Parallel AT attachment (ATA based on the 16 bit AT bus, also called ISA).
3. XT IDE (based on 8 bit ISA, obsolete).
4. MCA IDE (based on 16 bit micro channel, absolete).

The newer versions of parallel ATA  are refered to as ATA-2 and higher.  They are also sometimes called as EIDE (Enhanced IDE), Fast ATA, Ultra ATA, or Ultra DMA.

Parallel ATA standards:-

• ATA – 1
• ATA -2 (also called fast ATA, fast ATA-2, or EIDE.
• ATA – 3
• ATA – 4 (Ultra ATA 33)
• ATA – 5 (Ultra ATA 66)
• ATA – 6 (Ultra ATA 100)
• ATA – 7 (Ultra ATA 133 or SATA (serial ATA)
• ATA – 8 (ULtra ATA 166  or SATA

HARD DISK GEOMETRY

1. LBA  (Logical Block Addressing)

It is special mode used by the BIOS  for accessing the high capacity drivers.  In this method, the no. of cylinders are divided by a fixed number  and the no. of heads are multiplied by the same number.  Earlier bios uses 10 bits for addressing cylinders and 8 bits for addressing heads.  So, maximum no. of cylinders were 1024 and no. of heads were 256.  by using LBA method, we can connect a HDD with more than 1024 cylinders.

ZONE BIT RECORDING

In earlier hdd’s number of sectors per cylinder was constant.  So, the data in inner sectors were tightly written.  But in outer most sectors it was loosely packed. This reduces the data storage capacity.  Modern hdd’s uses a feature called ZBR to compensate this.  In ZBR total no. of cylinders are divided into different zones and each zone contains fixed no. of sectors.  This increases the data storage capacity of hdd.

SMART (Self Monitoring Analyzing and Reporting Technology)

If this feature is enabled, all the major events happening inside the hdd are monitored, analyzed and a warning will be given in advance if any problems which are likely to be happened in the near future.   

BUSMASTERING DMA

In present day HDD’s contains built-in DMA  controller.  It is mainly used for mass quantity of memory transfer to the system.  This feature is called bus mastering DMA.

SMALL COMPUTER SYSTEM INTERFACE (SCSI)

Small computer system interface, an ANSI standard, is  a parallel interface standard, used by apple macintosh computer PC’s and manay Unix systems for attaching peripherals device to computers.  SCSI interface provide for faster data transfer rates than standard serial and parallel ports.  In addition, lyou can attach many devices to a single SCSI port. 

SCSI standards are:-

Scsi version	Signaling rate MHZ	Bus width(bits)	Max data transfer MHZ	Maximum devices	Maximum cable length meters	Details /additional information
Scsi-1	5	8	5	7	6	8 bit bus and data rate of 5mbps 1986, 50 pin cable
Scsi-2	5	8	5	7	6	Same as above,  50 pin cable
Wide scsi	5	16	10	15	6	Use 68 pin cable.  16 bit bus.
Fast scsi	10	8	10	7	6	8bit bus, 10mbps speed 1990
Fast wide scsi	10	16	20	15	6	20mbps speed 16 bit bus1992
Ultra scsi	20	8	20	7	1.5	8bit bus 20 mbps data speed
Ultra scsi-2	20	16	40	7	12	Also called ultra wide scsi 1994
Ultra 2 scsi	40	16	80	15	12	Using 16 bit bus for data speed of 80mbps
Ultra 160 scsi	80	16	160	15	12	Also called wide ultra scsi

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