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HARD DISK DRIVE(HDD) CONTRUCTION & WORKING A hard disk drive (HDD), commonly referred to as a hard disk or hard drive, is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Early HDDs had removable media; however, an HDD today is typically a sealed unit with fixed media. Today three types of HDD available in market IDE HDD SATA HDD SCSI HDD


HARD DISK CONTRUCTION The hard disk drive constructed using following components. Disk platter Read/write head Head Arm/head slider Head Actuator mechanism Spindle motor Logic board Air filter Bezel Cable & IDE Connectors


PLATTERS A hard dish drive stores information on one or more flat circular discs called platters. The platters are mounted on a spindle, with spacers in between, and a motor on the bottom end of the spindle. These platters are made from aluminum alloy because of their strength & lightweight. The newer HDD uses glass & glass-ceramic platter. These platters are coated with magnetizable media. This media coating store information magnetically. Two types of recording media used in Hard disk drive: Iron oxide media Thin film media.


READ/WRITE HEAD It is used to read any information on the disk surface & to read the written data back, without any data loss. A hard disk drive contains one read/write head for each side of its platter. For example if a drive contains 3 platters then total six read/write head will be used to read the two sides or each platter. All head used in disk driven system are connected together & moved in & out on the disk surface as a single unit, one can’t move different head in different order. The HDD uses different types of head for read/write purpose, some them are as follows: Ferrite head Metal-in-gap head Thin film head Magneto-Resistive head Giant magneto resistive head


HEAD ARM/HEAD SLIDER The arm on which the read/write head of hard disk drive is located is called the head slider. These are made in catamaran sailboat shape. The small size slider has many advantages, such as the lower weight allow for faster acceleration & deceleration.


HEAD ACTUATOR MECHANISM The read/write head of the HDD is moved on the platter surface using head actuator mechanism. Two different head actuator mechanism are used: Steeper motor actuator Voice coil actuator The two-actuator mechanism work on completely different principle. Compare different characteristics of HDD actuator mechanism.


SPINDLE MOTOR It is used to rotate the hard disk drives platters. This motor directly connected to spindle on which the platters are connected, so it is vibration free. This motor works on a feedback loop to automatically adjust the rotation speed.


LOGIC BOARD Logic board control all these different parts of hard disk drive. It is also used to interface hard disk drive with the computer. The IDE type hard disk contains the drive controller circuit on the drive logic board. Many times the HDD failure is due to the failure of the logic board. A power problem or some other problem may destroy the logic board on the HDD.


AIR FILTER Most of your thinks that inside the HDD there is vacuum. But it is not true, the hard disk drive not work in vacuum condition. The read/write head need air to float on the disk surface. Nearly all HDD will have two air filter one is called re-circulating air filter & the second is called breather filter. These filter are permanently sealed inside the drive & are never to be changed for the life of the drive.


BEZEL/FRONT FACEPLATE Bezel is the front faceplate provided on most of the hard disk drives. Now a day the most HDD are connected internally & is hidden to the PC user.


CABLE & CONNECTORS Cable & connectors are used to connect the HDD to the main computer system. All the hard disk drive contains connectors for. Data/control interface connector Power connected


FEATURES OF HDD PATA (IDE) INTERFACE Parallel Advanced Technology Attachment (PATA) is a standard interface connecting storage devices such as hard disks & CD-ROM drive inside personal computers. Features of PATA Over 15 years of proven & reliable technology integration Up to 133 MB/s interface transfer rate Parallel ATA standards allow cable lengths up to only 18 inches (46 centimeters) Designed for desktop PCs & notebook PCs, with usage in entry servers electronics as well Parallel ATA (PATA) is based on the original IBM PC ISA bus.


SCSI INTERFACE SCSI is most commonly pronounced “scuzzy”. SCSI (Small Computer System Interface) is a set of standards for physically connecting & transferring data between computers & peripheral devices. The SCSI standards define commands, protocols, & electrical & optional interfaces. SCSI is most commonly used for hard disks & tape drives, but it can connect a wide range of other devices, including scanners, & optical drives (CD, DVD, etc.)


SATA INTERFACE Serial ATA (SATA) is a computer bus primarily designed for transfer of data between a computer & storage devices (like hard disks or optical drives). The main benefits are thinner cables that let air cooling work more efficiently, faster transfers, ability to remove devices while operating (Hot swapping), & more reliable operation with tighter data integrity checks. It was designed as a successor to the legacy Advanced Technology Attachment standard (ATA), &is expected to eventually replace the older technology (retroactively renamed Parallel ATA or PATA). Serial ATA adapters & devices communicate over a high-speed serial link.


FEATURES OF SATA It provides low cost storage for the industry or user. Improved speed & bandwidth, serves as an evolutionary replacement for the Parallel ATA interface. Implementation of Serial ATA allows for easy integration due to improved cabling. Greater flexibility in regard to system configuration & Hot plugability. Easily upgrade their storage device. Configuration of SATA device will be much simpler, with many of today’s requirement on jumper & settings no longer needed. Advancement in the SATA specifications also allow improvements & scalability in performance for the storage interface.


CD-ROM DRIVE CD-ROM (an abbreviation of “Compact Disc read-only memory”). CD-ROM discs are read using CD-ROM drives, which are now almost universal on personal computers. A CD-ROM drive may be connected to the computer via an IDE (ATA), SCSI, S-ATA, Firewire, or USB interface or a proprietary interface. The rate at which CD-ROM drives can transfer data from the disc is gauged by a speed factor relative to music CDs: 1x or 1- speed which gives a data transfer rate of 150 kilobytes per second in the most common data format. The drive consists of following components: A drive motor spins a disc. The drive motor is precisely controlled to rotate between 200 & 500 rpm depending on which track is being read. A laser & a lens system focus in on & read the bumps. A tracking mechanism moves the laser assembly so that the laser’s beam can follow the spiral track. The tracking has to be able to move the laser at micron resolution.

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Optical Head: A CD-ROM drive contains an optical head mounted on a sled or swing arm. This device shine a laser on the disc surface, then travels to the location of the data. After the optical head finds the data, it position itself within the spiral track & refocuses to read the data. The optical head is composed of three parts: These three parts enable the optical head to read data on the Disc. Laser Diode Lens Photo detector


WORKING OF CD-ROM DRIVE A CD-ROM drive operates by using a laser to reflect light off the bottom of the disc. The reflected light is then read by a photo detector. The overall operation of a CD-ROM drive is as follows: The laser diode emits a low-energy infrared beam towards a reflecting mirror. The servo motor, on command from the microprocessor, positions the beam on to the correct track on the CD-ROM by moving the reflecting mirror. When the beam hits the disc, its refracted light is gathered & focused through the first lens beneath the platter, bounced off the mirror, & sent toward the beam splitter The beam splitter directs the returning laser light toward another focusing lens.

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The last lens directs the light beam to a photo detector that converts the light into electric impulses. These incoming impulses are decode by the microprocessor & sent along to the host computer as data.


DVD DVD (also know as “Digital Versatile Disc” or Digital Video Disc”) is a popular optical disc storage media format used for data storage. Primarily uses are movies, software, & data backup purposes. A DVD is very similar to a CD, but it has a much larger data capacity. A standard DVD holds about seven times more data than a CD does.

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