Chapter 2 Storage Devices • Magnetic storage devices • Optical storage devices • Solid state devices • 4. Methods to prevent storage failures & data loss • 5. Impact of virus attack on computer system ITECC/TP/ECE/SimBN EC5103PA_Apr2008
Basic Principles of Magnetic Recording • The media(the disk) is coated with magnetic particles, the drive divides into microscopic areas called domains. • Each domain acts like a tiny magnet, with north and south poles, represents either ‘0’ or ‘1’ depending on which way it is pointing. • Information is read from, or written to, the media using a "head". • On a hard drive this head actually floats on a cushion of air created by the spinning of the disk. • Hard and floppy disk drives are "random access" devices because the information is organised into concentric circles on the surface of the disks. • This allows the head to go to any part of the disk and retrieve or store information quickly. • http://computer.howstuffworks.com/hard-disk.htm/printable • http://en.wikipedia.org/wiki/File:Hard_drive-en.svg
Hard Disk Drive • Most hard disks have two to eight inflexible platters coated with material that allows the magnetic recording of computer data. • A typical hard disk rotates at 7200 RPM and the read/write heads ride over the surface of the disk. • It is sealed to prevent contaminants. • 5400/10000/15000rpm • 20/40/80/120/160/300GB • PC's hard disk serves as a non-volatile, bulk storage medium and as the repository for a user's documents, files and applications. Fig 1 • 1997, IBM introduced the first hard drive with giant magnetoresistive (GMR) heads, the most advanced recording head enable data storage products with the industry's highest areal densities.
Capacity and Performance • two ways to measure performance of a hard disk: • Data rate - number of bytes per second that the drive can deliver to the CPU. • Seek time - amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. • capacity of the drive is the number of bytes it can hold.
Capacity & access speed • As of April 2009, the highest capacity HDDs are 2 TB. • A typical "desktop HDD" might store between 120 GB and 2 TB although rarely above 500GB of data (based on US market data) rotate at 5,400 to 10,000 rpm and have a media transfer rate of 1 Gbit/s or higher. Some newer have 3Gbit/s. • The fastest “enterprise” HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s. and a sustained transfer rate up to 125 MBytes/second. Drives running at 10,000 or 15,000 rpm use smaller platters to mitigate increased power requirements (due to air drag) and therefore generally have lower capacity than the highest capacity desktop drives. • "Mobile HDDs", i.e., laptop HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have lower capacity. A typical mobile HDD spins at 5,400 rpm, with 7,200 rpm models available for a slight price premium. Because of the TB(Terabytes)=1012 (1,000,000,000,000bytes) or 1000 gigabytes. GB= 109 (1,000,000,000bytes)
Capacity Full-height bays were found in old PCs in the early to mid-1980s, approximately 3.5" high by 5.75" wide, and used mainly for hard disks and floppy disk drives.
Close-up of a hard disk head resting on a disk platter, and its suspension. A reflection of the head and suspension are visible beneath on the mirror-like disk. An IBM HDD head resting on a disk platter. Since the drive is not in operation, the head is simply pressed against the disk by the suspension.
Microdrive (FYI, obsolete 2009) • Provides removable storage ranging from 340 MB, 500MB, 1 GB, 2GB, 4GB in a one-inch hard disk drive. • Integrates with a variety of handheld devices through use of the industry- standard CF+** Type II format and compatibility with PCMCIA Type II (with an adapter). • Provides reliable storage for digital cameras, handheld PCs, digital audio players, laptops, video camcorders, personal digital assistants (PDA) and other portable handheld devices. • Incorporates giant magnetoresistive (GMR) head technology, load/unload features for maximum capacity, performance, and reliability. • By 2009 all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory,
Basic Principles of Optical Storage • Optical storage refers to any storage device that uses laser light technology to retrieve and store data. • It stores information in deformities on the surface of a circular disc and reads this information by illuminating the surface with a laser diode and observing the reflection. • Optical disc storage is non-volatile. • The deformities may be permanent (read only media), formed once (write once media) or reversible (recordable or read/write media).
Types of Optical StorageMedia • Compact Disc (1982) : CD-R (1988) · CD-RW (1997) • DVD(1995) : DVD-RAM (1996) · DVD-R (1997) · DVD-RW (1999) · DVD+RW (2001) · DVD+R (2002) · DVD+R DL (2004) · DVD-R DL (2005) • Other : Microform (1870) · Optical tape (1995) · Laserdisc (1958) · UDO (2003) · ProData (2003) · UMD (2004) · Blu-ray Disc (2006) · HD DVD (2006) • Magneto-optic Kerr effect(1877): MO disc (1988) · MiniDisc (1991) • Optical Assist : Laser turntable (1986) · Floptical (1991) · Super DLT (1998)
Compatibility • http://en.wikipedia.org/wiki/Optical_drive
Compact Disk (CD) Optical Storage Devices • CDs and DVDs are used to hold music, data or computer software. • standard medium for distributing large quantities of information in a reliable package. • 1.2 mm thickness • 120mm diameter • store up to 640 (650) Mbytes of data or • 74 minutes of music (CD-A) • Replicated compact disk • Some CD-R blanks can hold 80 minutes of audio, or about 700MB of data.
Capacities of Compact Disc typeshttp://en.wikipedia.org/wiki/CD-ROM
Land ‘1’ Pit Bump ‘0’ Cross-section of a CD • It consists of an injection-molded piece of clear polycarbonate plastic. Bumps are impressed. These microscopic bumps are arranged as a single, continuous, long spiral track of data. • A thin, reflective aluminum layer is sputtered onto the disk, covering the bumps. • A thin acrylic layer is sprayed over the aluminum to protect it. • The label is then printed onto the acrylic Fig 2
Fig 3 Side-view of a CD Fig 5 pits and bumps Pits on aluminium side and bumps on the side where the laser read from 120 mm diameter Fig 4 CD-data in spiral form
CDROM drive • Consists of 3 components: • - A drive motor spins the disc. • - A laser and a lens system focus in on and read the bumps. • - A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track. Fig 6 Inside a CDROM drive
CDROM drives • The fundamental job of the CD player is to focus the laser on the track of bumps. The bumps reflect light differently than the "lands" (the rest of the aluminum layer), • Opto-electronic sensor detects that change in reflectivity. • The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes. http://electronics.howstuffworks.com/cd5.htm Fig 7 Block diagram of a CDROM player
LABEL COATING LACQUER REFLECTIVE DYE SURFACE POLYCARBONATE CD-Recordable (CDR) Fig 8 CDR layer Fig 9 Side-view of a CDR
An example of a CD-R burned in 2000 showing dye degradation. Part of the data on it has been lost.
Cleaning the CD R • The error correction of most modern optical drives/players can usually read effectively through fingerprints as well as a highly scratched information surface. • Dust can be removed from a CD's surface using compressed air or by very lightly wiping the information side with a very soft cloth (such as an eyeglass cleaning cloth) from the center of the disc in an outward direction. • Wiping the information surface of any type of CD in a circular motion around the center, however, has been known to create scratches in the same direction as the information and potentially cause data loss. • Fingerprints or stubborn dust can be removed from the information surface by wiping it with a cloth dampened with diluted dish detergent (then rinsing) or alcohol (methylated spirits or isopropyl alcohol) and again wiping from the center outwards, with a very soft, cloth (non-linting : polyester, nylon, etc.). • It is harmful, however, to use acetone, nail polish remover, kerosene, petrol/gasoline, or any other type of petroleum-based solvent to clean a CD-R; the use of petroleum based solvents will damage the polycarbonate surface and the CD-R will become unreadable.
Readability in CD drives • (December 2007)There was some incompatibility with CD-Rs and older CD-ROM drives. This was primarily due to the lower reflectivity of the CD-R disc. In general, CD-ROM drives marked as 8x or greater will read CD-R discs. Some DVD players will not read CD-Rs because of this change in reflectivity as well. • Burn speed can also affect the compatibility due to worse jitter on disks recorded at higher speeds; selecting a slower speed can improve compatibility, especially for CD-DA. • However, for writing some burners may not perform best at their lowest speed, and may not perform best on all discs at the same speed; each burner/media combination has an optimal speed which is most likely a lower rather than higher speed but can only be certainly known by testing that combination at different speeds (using disc checking software such as that which reports C1/C2 errors to compare the quality of readable discs.).
Write Laser Bump ‘0’ Fig 10 Comparison of CD and CDR Blank CD-R logic 1(translucent)
CD Burner Fig 11 Fig 12
Laser assembly inside a CD burner • To record data, the burner turns the laser writer on and off in synch with the pattern of 1s and 0s. • The laser darkens the material to encode a 0 and leaves it translucent to encode a 1. • Most CD burners can create CDs at multiple speeds. • At 1x speed, the CD spins at about the same rate as it does when the player is reading it. It takes 60 minutes to record 60 minutes of music. • At 2x speed, it would take about half an hour to record 60 minutes. • 1010000 = off on off on on on on write laser
Advantages & Disadvantages of a CD burner Advantages • The main advantage of CD-R discs is that they work in almost all CD players and CD-ROMS. • CD-Rs are relatively inexpensive. Disadvantages • can't reuse the discs. • Once you've burned in the digital pattern, it can't be erased and re-written.
Write Laser CD-Rewritable (CDRW) Fig 13 CDRW disk
CD-RW • CD-RW based on phase-change technology. • Two phases: 1. Amorphous phase (fluid) ‘0’ translucent - When the phase change compound is heated above its melting temperature (around 600 oC), it becomes a liquid. 2. Crystalline phase (solid) ‘1’ opaque, blank CD - At crystallization temperature (200 oC), it turns into a solid.
CD-Rewritable (CDRW) • CD RW drive has three laser powers : • Read • the lowest power which does not alter the state of the recording layer, so it can be used for reading the data. • Erase • the middle power which melts the recording layer and converts it to a reflective crystalline state • Write • the highest laser power which creates a non-crystalline (absorptive) state on the recording layer
DVD • for playback of large amounts of data. • Originally known as digital versatile disk or digital video disk. • Looks like CD-ROM. Same size as CD-ROM. • hold 4.7Gbytes of data • Up to 133 minutes of high-resolution video, with 720 dots of horizontal resolution (The video compression ratio is typically 40:1 using MPEG-2 compression.) • equivalent of 25 CD-ROMs • 8 hrs of CD-quality music/side. • Reasons for DVDs can store more data than CDs : • Higher-density data storage • Less overhead, more area • Multi-layer storage • http://en.wikipedia.org/wiki/DVD
MPEG-2 • MPEG-2 is an extension of the MPEG-1 international standard for digital compression of audio and video signals. • While MPEG-2 is the core of most digital television and DVD formats • MPEG-1 was designed to code progressively scanned video at bit rates up to about 1.5 Mbit/s for applications such as CD-i (compact disc interactive). • MPEG-2 is directed at broadcast formats at higher data rates; it provides extra algorithmic 'tools' for efficiently coding interlaced video, supports a wide range of bit rates and provides for multichannel surround sound coding. • http://en.wikipedia.org/wiki/DVD_region_codes
Region Codes • http://en.wikipedia.org/wiki/DVD_region_codes • DVD region codes are a DRM scheme. DVD video discs may be encoded with a region code restricting the area of the world in which they can be played. • Discs without region coding are called all region or region 0 discs. • The commercial DVD player specification requires that a player to be sold in a given place not play discs encoded for a different region (region 0 discs are not restricted). • The purpose of this is to allow motion picture studios to control aspects of a release, including content, release date, and, especially, price, according to the region. • Many DVD players are or can be modified to be region-free, allowing playback of all discs.
Region codes and countries 0 Informal term meaning "worldwide". Region 0 is not an official setting; discs that bear the region 0 symbol either have no flag set or have region 1–6 flags set. 1 Canada, United States; U.S. territories; Bermuda 2 Western and Central Europe; Western Asia; Israel, Iran, Egypt, Japan, South Africa, Swaziland, Lesotho; United Kingdom, Turkey, French overseas territories 3 Southeast Asia; South Korea; Taiwan; Hong Kong; Macau 4 Mexico, Central and South America; Caribbean; Australia; New Zealand; Oceania; 5 Ukraine, Belarus, Russia, Continent of Africa, Central and South Asia, Mongolia, North Korea. 6 People's Republic of China 7 Reserved for future use (found in use on protected screener copies of MPAA-related DVDs and "media copies" of pre-releases in Asia) 8 International venues such as aircraft, cruise ships, etc. ALL Region ALL discs have all 8 flags set, allowing the disc to be played in any locale on any player.
Fig 14 DVD layer format Fig 15 DVD pit layout Fig 16 Spiral track of data
DVD Player • A DVD player is very similar to a CD player. • It has a laser assembly that shines the laser beam onto the surface of the disc to read the pattern of bumps. • It consists of 3 components: • A drive motor spins the disc • A laser and a lens system focus in on and read the bumps. • A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track. • The fundamental job of DVD player is to focus laser on the track of bumps. • The hardest part of reading a DVD is keeping the laser beam centered on the data track. This centering is the job of the tracking system.
DVD Player • As the DVD is played, the tracking system has to move the laser continually outward. • As the laser moves outward, spindle motor must slow down the spinning of the DVD so that the bumps travel past laser at a constant speed, and the data comes off the disc at a constant rate. • If a DVD has a second layer, the start of that layer's data track can be at the outside of the disc instead of the inside. http://electronics.howstuffworks.com/dvd6.htm Fig 18 Reading the disc Near centre: Shorter radius x higher speed Away from centre:Longer radius x lower speed
Advantages of DVD Player Here are the typical contents of a DVD movie: • Up to 133 minutes of high-resolution video, in letterbox or pan-and-scan format, with 720 dots of horizontal resolution (The video compression ratio is typically 40:1 using MPEG-2 compression) • Soundtrack presented in up to eight languages using 5.1 channel Dolby digital surround sound • Subtitles in up to 32 languages DVD can also be used to store almost eight hours of CD-quality music per side.
Advantages of DVD Player • Watch high-quality movies with good sound. • DVD movies quality is better, and many of them have Dolby Digital or DTS sound, which is much closer to the sound you experience in a movie theater. • Skip to your favorite parts of movies • on-screen index • Play audio CDs • DVD players are compatible with audio CDs. • Watch movies in different picture formats • DVD movies have both the letterbox format, which fits wide-screen TVs, and the standard TV size format. • Watch movies with subtitles or in a different language • DVD movies may have several soundtracks on them, and they may provide subtitles in different languages
Formats supported by DVD Forum A. DVD-ROM • first DVD standard and a read-only format. • With MPEG-2 and Dolby Digital Surround Sound playback capabilities, it is ideal for full-length feature films and computer games with advanced graphics. • also for access to large amounts of data. B. DVD-R • write-once • for authoring and testing DVD titles, limited distribution DVD publishing. • Single-sided DVD-R discs store 3.9GB of data. • two additional standards : • DVD-RG for general use, • DVD-RA for authoring, which is used for mastering • DVD video or data and is not typically available to the general public.
DVD Media Types C. DVD-RAM • rewritable function. • 2.6GB, 4.7GB or 9.4GB (double-sided)) • For applications as data back up, document archiving, multimedia titles and presentations. • to record and re-record on one disc over 100,000 times • is compatible only with devices manufactured by the companies that support the DVD-RAM format. • DVD-RAM discs are typically housed in cartridges. D. DVD-RW • rewritable version of DVD-R, 4.7GB per disk. • an authoring tool as well as for archiving data. • uses DVD-R media, but is rewriteable up to 1000 times. • DVD-RW records data sequentially • DVD-RAM provides random access to recorded data.
DVD Media Types E. DVD-Audio • read-only optical disk for playback of high-quality audio. • It supports bit depths up to 24-bit and sample rates up to 192 kHz, while CD audio is 16-bit, 44.1 kHz. • Supporting a wide range of digital audio options, • offer consumers a superior listening experience. F. DVD-Video • a consumer video format used to store digital video on DVD (DVD-ROM) discs. • using the DVD-Video specification require a DVD drive and an MPEG-2 decoder (e.g. a DVD player, or a DVD computer drive with a software DVD player). • Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and audio of varying formats. • Each DVD-Video disc contains one or more region codes, denoting the area(s) of the world in which distribution and playback are intended.
DVD Media Types F) DVD-R DL • (DL stands for Dual Layer), • also called DVD-R9, is a derivative of the DVD-R format standard. DVD-R DL discs hold 8.54 GB by utilizing two individual recordable dye layers on a single-sided DVD disc. • Dual Layer is more commonly called Double Layer in the consumer market,. Discs can be read in many DVD devices (older units are less compatible) and can only be written using DVD-R DL compatible recorders. H) DVD-AR • DVD-AR DL is a recordable version of DVD-Audio. I) HD-DVD • HD DVD or High-Definition Digital Versatile Disc is a high-density optical disc format designed for the storage of data and high-definition video. • It has a single-layer capacity of 15 GB, and a dual-layer capacity of 30 GB.
Formats supported by DVD+RW Alliance: A) DVD+R • can record up to 4.7 GB single-layered/single-sided DVD+R disc, at up to 16x speed. • can record only once. B) DVD+RW • can record up to 4.7 GB at up to 16x speed. • can be overwritten several times. It does not need special "pre-pits" or finalization to be played in a DVD player. C) DVD+R DL • (also called DVD+R9) is a derivate of DVD+R that uses dual-layer recordable discs to store up to 8.5 GB of data.
Blu-ray Disc • also known as Blu-ray or BD • is an optical disc storage media format • main uses are high-definition video and data storage. • same dimensions as a standard DVD or CD. • blue-violet laser isused to read and write the disc. • Because of its shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red (650 nm) laser. • A dual layer Blu-ray Disc can store 50 GB, almost six times the capacity of a dual layer DVD.