HARD DISK DRIVE

&

OPTICAL DISC

MEMBERS OF PROJECT (HDD)

MEMBERS OF PROJECT (OD)

HARD DISC DRIVE

INTRODUCTION

A hard disk drive (HDD; also hard drive, hard disk, or disk drive) is a device for storing and retrieving digital information, primarily computer data. It consists of one or more rigid (hence "hard") rapidly rotating discs (platters) coated with magnetic material, and with magnetic heads arranged to write data to the surfaces and read it from them. Hard drives are classified as non-volatile, random access, digital, magnetic, data storage devices.

HistoryHard disk drives were introduced in 1956 as data storage for an IBM real-time transaction processing computer and were developed for use with general purpose mainframe and mini computers. The first IBM drive, the 350 RAMAC, was approximately the size of two refrigerators and stored 5 million 6-bit characters on a stack of 50 discs.

In 1961 IBM introduced the model 1311 disk drive, which was about the size of a washing machine and stored two million characters on a removable disk "pack." Users could buy additional packs and interchange them as needed, much like reels of magnetic tape.

As the 1980s began, hard disk drives were a rare and very expensive additional feature on personal computers (PCs); however by the late '80s, their cost had been reduced to the point where they were standard on all but the cheapest PC.

External hard disk drives remained popular for much longer on the Apple Macintosh. Every Mac made between 1986 and 1998 has a SCSI port on the back, making external expansion easy; also, "toaster’’.

Technology

Magnetic recording

A hard disk drive records data by magnetizing a thin film of ferromagnetic material on a disk. Sequential changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. User data is encoded using an encoding scheme, such run-length limited encoding, which determines how the data is represented by the magnetic transitions.

The magnetic surface of each platter is conceptually divided into many small sub-micrometer-sized magnetic regions, referred to as magnetic domains, (although these are not magnetic domains in a rigorous physical sense), each of which has a mostly uniform magnetization.

Components 

HDD with disks and motor hub removed exposing copper colored stator coils surrounding a bearing in the center of the spindle motor. Orange stripe along the side of the arm is thin printed-circuit cable, spindle bearing is in the center and the actuator is in the upper left.

A typical hard disk drive has two electric motors; a disk motor that spins the disks and an actuator (motor) that positions the read/write.

The hard drive's electronics control the movement of the actuator and the rotation of the disk, and perform reads and writes on demand from the disk controller.

Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed.

Error handling

Modern drives make extensive use of error correction codes (ECCs), particularly Reed–Solomon error correction. These techniques store extra bits, determined by mathematical formulas, for each block of data; the extra bits allow many errors to be corrected invisibly.

The extra bits themselves take up space on the hard drive, but allow higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage capacity.

In the newest drives of 2009, low-density parity-check codes (LDPC) were supplanting Reed-Solomon; LDPC codes enable performance close to the Shannon Limit and thus provide the highest storage density available.

Future development

Due to bit-flipping errors and other issues, perpendicular recording densities may be supplanted by other magnetic recording technologies. Toshiba is promoting bit-patterned recording (BPR), while Xyratex is developing heat-assisted magnetic recording (HAMR).

October 2011: TDK has developed a special laser that heats up a hard disk's surface with a precision of a few dozen nanometers. TDK also used the new material in the magnetic head and redesigned its structure to expand the recording density. This new technology apparently makes it possible to store one terabyte on one platter and for the initial hard drive TDK plans to include two platters.

Capacity

The capacity of an HDD may appear to the end user to be a different amount than the amount stated by a drive or system manufacturer due to amongst other things, different units of measuring capacity, capacity consumed in formatting the drive for use by an operating system and/or redundancy.

In December 1998, an international standards organization attempted to address these dual definitions of the conventional prefixes by proposing unique binary prefixes and prefix symbols to denote multiples of 1,024, such as “mebibyte (MiB)”, which exclusively denotes 220 or 1,048,576 bytes.

In the over‑13 years that have since elapsed, the proposal has seen little adoption by the computer industry and the conventionally prefixed forms of “byte” continue to denote slightly different values depending on context.

Access and interfaces

Hard disk drives are accessed over one of a number of bus types, including as of 2011 parallel ATA (PATA, also called IDE or EIDE; described before the introduction of SATA as ATA), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel.

Bridge circuitry is sometimes used to connect hard disk drives to buses with which they cannot communicate natively, such as IEEE 1394, USB and SCSI.

Modern hard drives present a consistent interface to the rest of the computer, no matter what data encoding scheme is used internally.

External removable drives

3.0 TB 3.5" Seagate FreeAgent GoFlex plug and play external USB 3.0-compatible drive (left), 750 GB 3.5" Seagate Technology push-button external USB 2.0 drive (right), and a 500 GB 2.5" generic brand plug and play external USB 2.0 drive (front).

External removable hard disk drives typically connect via USB. Plug and play drive functionality offers system compatibility, and features large storage options and portable design.

External hard disk drives are available in 2.5" and 3.5" sizes, and as of March 2012 their capacities generally range from 160GB to 2TB. Common sizes are 160GB, 250GB, 320GB, 500GB, 640GB, 1TB, and 2TB.

AdvantagesLarge storage capacity.

Stores and retrieves data much faster than a floppy disk or CD-ROM.

Data is not lost when you switch off the computer.

Usually fixed inside the computer so cannot get mislaid.

Cheap on a cost per megabyte compared to other storage media.

Hard disks can be replaced and upgraded as necessary.

Can have two hard disks in a machine, one can act as a mirror of the other and create a back up copy.

Disadvantages

Hard disks eventually fail which stops the computer from working.

Regular 'head' crashes can damage the surface of the disk, leading to loss of data in that sector.

The disk is fixed inside the computer and cannot easily be transferred to another computer .

OPTICAL DISC’S

INTRODUCTION

In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc which encodes binary data (bits) in the form of pits (binary value of 0 or off, due to lack of reflection when read) and lands (binary value of 1 or on, due to a reflection when read) on a special material on one of its flat surfaces.

Optical discs are usually between 7.6 and 30 cm (3 to 12 in) in diameter, with 12 cm (4.75 in) being the most common size.

An optical disc is designed to support one of three recording types: read-only (e.g.: CD and CD-ROM), recordable (write-once, e.g. CD-R), or re-recordable (rewritable, e.g. CD-RW.

Optical discs are most commonly used for storing music (e.g. for use in a CD player), video (e.g. for use in a Blu-ray player), or data and programs for personal computers (PC).

History

The optical disc was invented in 1958. In 1961 and 1969, David Paul Gregg registered a patent for the analog optical disc for video recording. This form of optical disc was a very early form of the DVD U.S. Patent 3,430,966. It is of special interest that U.S. Patent 4,893,297, filed 1989, issued 1990, generated royalty income for Pioneer Corporation's DVA until 2007 then encompassing the CD, DVD, and Blu-ray systems.

Later, in the Netherlands in 1969, Philips Research physicists began their first optical videodisc experiments at Eindhoven. In 1975, Philips and MCA began to work together, and in 1978, commercially much too late, they presented their long-awaited Laserdisc in Atlanta.

In Japan and the U.S., Pioneer succeeded with the videodisc until the advent of the DVD. In 1979, Philips and Sony, in consortium, successfully developed the audio compact disc.In the mid-1990s, a consortium of manufacturers developed the second generation of the optical disc, the DVD.

 First-generation

Initially, optical discs were used to store music and computer software. The Laserdisc format stored analog video signals for the distribution of home video, but commercially lost to the VHS videocassette format, due mainly to its high cost and non-re-recordability; other first-generation disc formats were designed only to store digital data and were not initially capable of use as a digital video medium.

Compact Disc (CD) and derivatives Video CD (VCD) Super Video CD

LaserdiscGD-ROMPhase-change DualDouble Density Compact Disc (DDCD)Magneto-optical discMiniDisc

Second-generationSecond-generation optical discs were for storing great amounts of data, including broadcast-quality digital video. Such discs usually are read with a visible-light laser (usually red); the shorter wavelength and greater numerical aperture allow a narrower light beam, permitting smaller pits and lands in the disc. In the DVD format, this allows 4.7 GB storage on a standard 12 cm, single-sided, single-layer disc; alternatively, smaller media, such as the DataPlay format, can have capacity comparable to that of the larger, standard compact 12 cm disc.

DVD and derivatives DVD-Audio DualDisc Digital Video Express (DIVX)

Super Audio CDEnhanced Versatile DiscDataPlayUniversal Media DiscUltra Density Optical

Third-generation

Third-generation optical discs are in development, meant for distributing high-definition video and support greater data storage capacities, accomplished with short-wavelength visible-light lasers and greater numerical apertures. Blu-ray Disc and HD DVD uses blue-violet lasers and focusing optics of greater aperture, for use with discs with smaller pits and lands, thereby greater data storage capacity per layer. In practice, the effective multimedia presentation capacity is improved with enhanced video data compression codecs such as H.264/MPEG-4 AVC and VC-1.

High-Definition Disc: Blu-ray Disc (up to 128 GB (quad-layer)) CBHD (a derivative of the discontinued disc format HD DVD)

In development: Forward Versatile Disc Digital Multilayer Disk or Fluorescent Multilayer Disc

Fourth-generation

The following formats go beyond the current third-generation discs and have the potential to hold more than one terabyte (1 TB) of data:

Holographic Versatile Disc

Protein-coated disc

Advantages and Disadvantages of Optical Disk:-

Advantage:

Cheap media.

CD & DVD can hold lots of media.

Easy to carry

Small in size.

looks cool.

Disadvantages

Easy to scratch.

Easy to break.

Can get damaged.

Small capacity compared to some flash/thumb drive.

Wikipedia

Yahoo answers

(Ppt prepared by Vishal Rai)

REFERENCE

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