MOD002556
03/03/2014
13:00-16:00
Magnetic storage (or magnetic recording) is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.
As of 2013, magnetic storage media, primarily hard disks, are widely used to store computer data as well as audio andvideo signals. In the field of computing, the term magnetic storage is preferred and in the field of audio and video production, the term magnetic recording is more commonly used. The distinction is less technical and more a matter of preference. Other examples of magnetic storage media include floppy disks, magnetic recording tape, and magnetic stripes on credit cards.
Access Time= Seek time + latency
Seek time= Average time to locate required cylinder
time to traverse 1/2 the cylinders
Latency=
Average wait for required sector
1/2 rotation period
RAID is a data storage technology that combines multiple disk drive components into a logical unit for the purposes of data redundancy and performance improvement.[1] Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the specific level of redundancy and performance required.
The term "RAID" was first used by David Patterson, Garth A. Gibson, and Randy Katz at the University of California, Berkeley in 1987, standing for redundant array of inexpensive disks.[2] Industry RAID manufacturers later tended to interpret the acronym as standing for redundant array of independent disks.[3][4][5][6]
RAID is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple physical drives: RAID is an example of storage virtualization and the array can be accessed by the operating system as one single drive.[note 1] The different schemes or architectures are named by the word RAID followed by a number (e.g. RAID 0, RAID 1). Each scheme provides a different balance between the key goals: reliability and availability, performance and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable (sector) read errors, as well as whole disk failure.
Compact disc (CD) is a digital optical disc data storage format. The format was originally developed to store and play back sound recordings only (CD-DA), but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. Audio CDs and audio CD players have been commercially available since October 1982.
Standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to about 80 minutes of uncompressed audio or 700 MiB(actually about 703 MiB or 737 MB) of data. The Mini CD has various diameters ranging from 60 to 80 millimetres (2.4 to 3.1 in); they are sometimes used for CD singles, storing up to 24 minutes of audio or delivering device drivers.
At the time of the technology's introduction it had much greater capacity than computer hard drives common at the time. The reverse is now true, with hard drives far exceeding the capacity of CDs.
In 2004, worldwide sales of CD audio, CD-ROM, and CD-R reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide.[1] Compact discs are increasingly being replaced or supplemented by other forms of digital distribution and storage, such as downloading and flash drives, with audio CD sales dropping nearly 50% from their peak in 2000.[2]
Blu-ray Disc (BD) is a digital optical disc data storage format designed to supersede the DVD format, in that it is capable of storinghigh-definition video resolution (1080p). The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs.[4]Conventional (pre-BD-XL) Blu-ray Discs contain 25 GB per layer, with dual layer discs (50 GB) being the industry standard for feature-length video discs. Triple layer discs (100 GB) and quadruple layers (128 GB) are available for BD-XL re-writer drives.[5] The name Blu-ray Disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs. The major application of Blu-ray Discs is as a medium for video material such as feature films. Besides the hardware specifications, Blu-ray Disc is associated with a set of multimedia formats. Generally, these formats allow for the video and audio to be stored with greater definition than on DVD.
High-definition video may be stored on Blu-ray Discs with up to 1080p resolution (1920×1080 pixels), at up to 60 (59.94) fields per second. The older DVD discs had a maximum resolution of 480p (NTSC, 720×480 pixels) or 576p (PAL, 720×576 pixels).
The format was developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. Sony unveiled the first Blu-ray Disc prototypes in October 2000, and the first prototype player was released in April 2003 in Japan. Afterwards, it continued to be developed until its official release in June 2006. As of June 2008, more than 2,500 Blu-ray Disc titles were available in Australia and the United Kingdom, with 3,500 in the United States and Canada.[6] In Japan, as of July 2010, more than 3,300 titles have been released.[7]
During the high definition optical disc format war, Blu-ray Disc competed with the HD DVD format. Toshiba, the main company that supported HD DVD, conceded in February 2008,[8] releasing its own Blu-ray Disc player in late 2009.[9]
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