CDs Cont CSIT 301 Blum 1 Fixing Mistakes

CD’s (Cont. ) CSIT 301 (Blum) 1

Fixing Mistakes • CDs have a lot of ECC so that errors can be fixed. • If the data for a given sample cannot be recovered using ECC, one can interpolate. Assume the bad sample is halfway between the previous and the next sample. • Interpolation is not available to CDs used to store data, so they have even more space devoted to ECC. CSIT 301 (Blum) 2

CD-DA Recap • The CD-DA standard as set out in the “Red Book, ” defines a sector or block of 3234 bytes. • Of those 3234 bytes, – 2352 are actual audio data – 98 are control (analog of servo information, synchronization and location) – 784 are EDC/ECC CSIT 301 (Blum) 3

CD-DA Percentages • Each CD-DA block or sector is – 72. 7% actual audio data – 24. 2% EDC/ECC – 3% control data • For every 8 bits of data, there are 3 more bits of control/error data. • If a CD-DA error cannot be corrected, one can interpolate. CSIT 301 (Blum) 4

CD-ROM • The red-book CD-DA standards were adapted by the “Yellow Book” standards to handle non-audio data, i. e. regular data files, programs, etc. • These standards are for CD-ROMs, compact disc – read only memory – information written by the manufacturer and not changed by the user. CSIT 301 (Blum) 5

CD-ROM Mode 1 • CD-ROM Mode 1 starts with the basic CD-DA sector division 3234 = 98 (control) + 784 (error) + 2352 (data) and devotes some of the data portion to additional error code and control yielding 3234 = 98 (control) + 784 (error) + 304 (more error/control) + 2048 (data). CSIT 301 (Blum) 6

CD-ROM Mode 1 Percentages • Each CD-ROM block or sector is – 63. 3% actual data – 33. 6% EDC/ECC – 3% control data • More than one-third error detection and error correction code CSIT 301 (Blum) 7

Less Data/Fewer Errors/More Control • The CD-ROM standards impose more control because one must be able to locate data with more precision. • The CD-ROM standard imposes more error detection and error correction because by the nature of the data it stores it does not have available the interpolation approach to dealing with errors that CD-DA does. CSIT 301 (Blum) 8

Speeds • The 150 KB/s is the base data transfer rate for CD-ROM. • Higher speeds are reported as multiplicative factors of this base: 2 , 3 , etc. • Recall that as disc speeds got higher, they switched from CLV (constant data rate) to CAV (variable data rate). • The latter data rates may be reported with the term “Max” to indicate that the reported data rate is the maximum of the range (i. e. When one is on the outer edge of the CD). • Such drives must still support CLV at lower speeds so that they can play audio CDs. CSIT 301 (Blum) 9

CSIT 301 (Blum) 10

The Other Speed Factor • The data transfer rate is the rate for reading consecutive data. Another speed factor is average access time which is the typical time required to locate a “random” address. • As with hard disks, this involves the radial positioning of the head (seek time) and the angular spinning of the disk (latency). CSIT 301 (Blum) 11

CD-R • As typical files grew larger and larger, the limitations of the floppy disk as a software/data delivery mechanism became evident. • The CD-ROM had hundreds of times the capacity of a floppy, but was limited in that it was “read only. ” The standards essentially required a manufacturing process to write data. • So the CD-R standards were introduced. They are laid out in the orange book mainly by Phillips in 1990. CSIT 301 (Blum) 12

CD-R • CD-R (compact disc, recordable) are also sometimes known as CD-WORM (write once read many) or just CD-WO (write once). • While the Yellow Book, Green Book and White Book outline variations in the logical overlay of the physical specifications laid out in the Red Book, the Orange book must outline new physical requirements that allow a user to record a CD. • Basically the same logical overlay as CD-ROM will be maintained for compatibility. CSIT 301 (Blum) 13

Changing Medium • Recall that a CD-ROM is stamped from a master. The stamping provides the pits. When reading, the pits and distinguished from the lands because the lands yield specular reflection (clean, organized) while the pits yield diffuse reflection (scattered). – Think of light reflecting off a mirror versus light reflecting a rippling body of water (pool, lake, etc. ) • So all that is needed is to produce this change in the way light is reflected. CSIT 301 (Blum) 14

Before Recording (Burning) • A CD-R starts off with a plastic substrate. The substrate is not flat, rather it has a wobbly spiral groove. – Think of it as lined paper, the lines guide us as to where we will write the information. • On top of the plastic is a photosensitive dye. • On top of that is the reflective layer (gold, silver or aluminum alloy). • On top of that is a protective layer of plastic. • On top of that is the label. CSIT 301 (Blum) 15

Before Burning From http: //entertainment. howstuffworks. com/cd-burner 2. htm CSIT 301 (Blum) 16

Photosensitive Dye • The chemical between the plastic and the metal is photosensitive, meaning that it changes its properties when exposed to light. (like film) – The process is known as burning. • In this case the light is laser light, the changes are permanent, and the important aspect here is that the changed property affects the way light is reflected. CSIT 301 (Blum) 17

After Burning CSIT 301 (Blum) 18

All at once? • The recording is permanent but it does not necessarily have to be done all at once. • If the recording is allowed to be done in more than one sitting, then the recording is said to be multi-session as opposed to single-session. • Another term is Track-At-Once (TAO) versus Disc-At-Once (DAO). CSIT 301 (Blum) 19

Table of Contents • A CD-ROM has a table of contents (TOC) at the beginning. It serves a similar purpose to the file allocation table and root directory found on a hard disk, it allows the files to be found. – A. k. a. index of the disc. • Multi-session CDs allow data to be written in various sessions, that is for data to be appended (not overwritten) at a later time. – Such CDs have a table of contents for each session. – The new TOC contains the old info plus the new. – Such CDs cannot be read by ordinary drives unless they are “finalized”. CSIT 301 (Blum) 20

Single Session vs. Multiple Session • With single-session CDs, the TOC is easily located by the drive. Multi-session CDs drives need to be able to find the latest TOC. • Many older CD drives do not have this capability. • Reading a CD-RW requires a multi-session capability, so it is becoming standard. CSIT 301 (Blum) 21

CD-R Drive • The burning of a CD requires a special laser, different from the one in an ordinary CD-ROM drive used for reading. • CD-Rs can typically handle many of the various logical formats (CD-DA, CD-ROM, CD-I, etc. ) • A CD-R drive can also read. Typically it reads at a higher speed than it writes. • Writing a CD requires a steady flow of data and can be demanding. – Early on, simple CD-ROM drives were often IDE/ATAPI but CD-R drives were more likely to be SCSI, which tend to perform better and allow other things to occur simultaneously. CSIT 301 (Blum) 22

Keep that data flowing • To keep the flow of data steady, a CD-R drive may use a buffer. • Another approach is to make an image of the disc to be burned on the hard drive (collect all the files from their various locations, add the error code, etc. ) and then have a nice, steady, fast continuous read of consecutive data. CSIT 301 (Blum) 23

Usefulness of CD-R • CD-Rs had floppies beat on capacity by a (multiplicative) factor of several hundred, but floppies could be written and re-written. • For files that are in the editing/updating process, the ability to rewrite is crucial. – CD-Rs have come down in price, but they’re too expensive to be thrown away regularly – let alone the impact that would have on the environment. CSIT 301 (Blum) 24

CD-RW • CD-Rs are “write once” because the photosensitive dye is permanently changed when it is written/burned. • In CD-RW this material is replaced with a phasechange layer. – A phase is a state that a material can be in. For example, H 2 O can be in one of three phases: ice (solid), water (liquid), stream (gas). – Materials may have several different solid phases. • A phase is stable (the material can remain in a given phase indefinitely), but a phase change is reversible (heating for example may return the material to its original state). CSIT 301 (Blum) 25

Phase change CSIT 301 (Blum) 26

Dr Jekyll and Mr Hyde • The two phases in question are a matter of how “organized” the material is. • In one phase, the material is a very orderly crystal that reflects light specularly. • In the other phase, the material is disorderly and reflects light diffusely. • Heating the material a little can give it a little bit of movement and flexibility so it can organize. Heating it up a lot throws it into disorder, but it cools quickly (quenches) and remains in the disorderly state. CSIT 301 (Blum) 27

The price one pays • The differences in these phases is more subtle than the differences in CD-ROMs and CD-Rs. • Thus a drive must have a more sensitive photo-detector in order to read a CD-RW. • Many older (“legacy”) drives do not have such a sensitive detector and cannot read CD-RWs. CSIT 301 (Blum) 28

Digital Versatile/Video Disk (DVD) • The size of software and data files continues to grow, so the CD with its 650 MB capacity is becoming too limited. • A newer, higher capacity alternative is the DVD which stands for either digital video disk or digital versatile disk. – Although some will now say DVD doesn’t stand for anything. CSIT 301 (Blum) 29

DVDs • A DVD is just a variation on a CD, information is read from the disc by reflecting light from its surface. • The differences between DVDs and CDs is a matter of speed and capacity (DVDs are better on both counts) and logical format. • As with CDs there are various formats and one has to be careful about compatibility. – Many DVD standards are maintained by ECMA. CSIT 301 (Blum) 30

ECMA CSIT 301 (Blum) 31

DVD-R Standards Page CSIT 301 (Blum) 32

DVD-R Standards Page (cont. ) CSIT 301 (Blum) 33

Viva la difference • A different laser – A DVD laser has a wavelength of 636 nm or 650 nm compared to a CD laser having a wavelength of 780 nm. • The nm stands for nanometer, that’s 10 -9 m, a billionth of a meter. – With a smaller wavelength, one can “resolve” (distinguish) smaller/closer objects. In this case, the smaller wavelength allows the pits and the lands to be smaller and closer together on a DVD than on a CD. CSIT 301 (Blum) 34

Waves with different wavelengths CSIT 301 (Blum) 35

Electromagnetic spectrum ←Wavelength getting smaller Red light has a smaller wavelength than IR (infrared). Blue light (used by Blu-Ray) has an even smaller wavelength. CSIT 301 (Blum) 36

Smaller Pits Higher Density/Capacity CSIT 301 (Blum) 37

DVD Pits CSIT 301 (Blum) 38

Another Difference • The Error Correction Code (ECC) used in DVDs is more efficient. – As with CDs the amount and type of ECC will vary between DVDs used for multimedia and DVDs used for “regular” files. • DVDs also use a somewhat larger area for recording. CSIT 301 (Blum) 39

CSIT 301 (Blum) 40

Result: Higher Capacity • The previous factors result in a DVD having several times the capacity of a CD. – DVD capacity is approximately 4. 7 GB (minimum) compared to CD-ROM capacity of 650 MB – about seven times larger. – Caution: In DVD standards GB means 109 (1, 000, 000) instead of 230 (1, 073, 741, 824). CSIT 301 (Blum) 41

Higher Speeds • DVDs have a higher standard data transfer rate – 1. 32 MB/s compared to 150 KB/s for CD-DA – about nine times faster. – This speed specification is for video viewing. When DVDs are used for non-video data, they can be operated at higher speeds, which are reported as multiplicative factors of the standard: 2 X, 3 X etc. – Older DVD-ROM drives used CLV, now they tend to use CAV. In the latter case, the maximum multiplicative factor is reported, e. g. 16 X max. CSIT 301 (Blum) 42

Sizes, Sides and Layers • DVDs come in two standard sizes: diameter 80 mm or diameter 120 mm (standard CD size). • DVDs can be single-sided (SS) or doubled-sided (DS), effectively two DVDs glued together. • A DVD can be single layer (SL) or double layer (DL). – The upper layer is semi-transparent, so one can see through to the second layer of data. CSIT 301 (Blum) 43

Single Versus Double Layer The laser is focused on the different layers at different times. CSIT 301 (Blum) 44

Numbers and Capacities • • • DVD-5: single-sided, single-layered 4. 7 GB DVD-9: single-sided, double-layered 8. 5 GB DVD-10: double-sided, single-layered 9. 4 GB DVD-14: double-sided, mixed layers 13. 2 GB DVD-18 double-sided, double-layered 17 GB – Still uncommon CSIT 301 (Blum) 45

Layers and Sides CSIT 301 (Blum) 46

UDF • There was some attempt to avoid the pitfalls of the CD situation (so many formats) and out of that came UDF. – Of course, they didn’t succeed, there a number of DVD formats. • UDF stands for Universal Disk Format. • “UDF, defined by the Optical Technology Storage Association (OTSA), is a subset of ISO 13346, an interchange standard for non-sequential recording of data. ” CSIT 301 (Blum) 47

UDF (Cont. ) • It is a file system used for DVDs and optical media in general. – Some CDs can use it. • It is “universal” in that all of the major DVD vendors have agreed to use it. • It is also “universal” in that data files and multimedia files are not treated separately. • It allows the operating system to understand what is on a DVD. CSIT 301 (Blum) 48

Various Formats • In addition to the different physical formats, there a number of different application formats and the accompanying compatibility issues. – DVD+R, DVD+RW, DVD-RAM, DVD-RW, DVD-ROM • DVD drives are usually “backward compatible” in that they can read most CD formats. CSIT 301 (Blum) 49

DVD-Video and DVD-ROM • Analogous to CD-DA (for music) and CDROM (for data) are DVD-Video (for movies) and DVD-ROM (for data). – An DVD player may only be able to read DVDVideo, whereas a DVD drive will be able to read DVD-ROM as well as DVD-Video. • These standards are read only. The information is stamped or pressed onto the disc by a manufacturer. CSIT 301 (Blum) 50

MPEG 2 • MPEG 2 is part of the DVD-Video standard. It describes how multimedia files can be compressed (50 -to-1). • MPEG stands for Moving Picture Experts Group. – MPEG is part of ISO. • There are three major MPEG standards: MPEG-1, MPEG-2 and MPEG-4. • The decoding can be done by software or hardware. CSIT 301 (Blum) 51

MPEG Uses 1. Discrete Cosine Transform (DCT). 2. Quantization, selectively throwing away information that won’t be missed (“lossy compression”). 3. Huffman coding, a lossless compression technique that uses code encoding frequently occurring data with short codes and infrequently occurring data with long codes. 4. Motion compensated predictive coding: encode changes from one frame to the next rather than encoding each new frame in its entirety. 5. Bi-directional prediction like interpolation discussed in CD-DA. CSIT 301 (Blum) 52

Recordable • As with CD-R, making a recordable DVD requires some changes in the physical medium. – The writing is not done by pressing but by exposing the DVD-R’s photo-sensitive dye layer to light and “burning” the information on it. CSIT 301 (Blum) 53

Rewritable • As with CDs, to achieve rewritability, one must replace the photosensitive material which is permanently burned with “phase change” material. – The phase change material in DVD RW means that they do not reflect as strongly as DVD-ROM or DVD-R. This makes them harder to read. – Sometime drives have trouble distinguishing between double layered DVDs and DVD-RW. CSIT 301 (Blum) 54

The Competition • There are three competing technologies for rewritable DVDs – DVD-R – DVD+R – DVD-RAM CSIT 301 (Blum) 55

DVD-RW • A. k. a. DVD-ER and DVD-R/W • Can be written about 1000 times • There is a distinction with DVD-RW discs – 1. 1 do not support CPRM (Content Protection for Removable Media) – 1. 1 B do support CPRM • Apple and Compaq CSIT 301 (Blum) 56

CPRM • Content Protection for Removable Media (CPRM) enforces copy protection restrictions using a mechanism built into the storage medium itself. • Based on broadcast encryption, the CPRM system would incorporate “tags” into storage media. • Controversial, other alternative pursued. CSIT 301 (Blum) 57

DMCA • Stands for Digital Millennium Copyright Act (a update of copyright law from 1998). – “It is a crime to circumvent anti-piracy measures that are built into commercial software. ” – “It is a crime to manufacture, sell or distribute codecracking devices that illegally copy software. However, it is not a crime to crack copyright protection devices in order to conduct encryption research, assess product interoperability or test the security of computer systems. ” – Etc. CSIT 301 (Blum) 58

DVD-RAM • Better access speeds • Can be written 100, 000 times • Uses a cartridge (for better medium protection) • Standard DVD drives don’t support the cartridge. You may lose rewritability if you remove them from the cartridge. • Hitachi, Panasonic and Toshiba CSIT 301 (Blum) 59

DVD+RW • Written to 1, 000 times • No cartridge • Not officially a standard of the DVD Forum but backed by Sony and HP. • Records video well. • DVD+R is a write-once technology that is compatible with DVD+RW. CSIT 301 (Blum) 60

DVD-Audio versus Audio CD Sampling Rate Number of Levels CD 44, 100 Hz 216 = 65, 536 DVD 192, 000 Hz 224 = 16, 777, 216 CSIT 301 (Blum) 61

Is DVD-Audio overkill? CSIT 301 (Blum) 62

Blu-Ray CSIT 301 (Blum) 63

Viva la difference (Again) • A different laser – Blu-Ray uses a laser diode with wavelength 405 nm compared to a DVD laser of 636 nm or 650 nm compared to a CD laser of 780 nm. • The nm stands for nanometer, that’s 10 -9 m, a billionth of a meter. – With a smaller wavelength, one can “resolve” (distinguish) smaller/closer objects. In this case, the smaller wavelength allows the pits and the lands to be smaller and closer together on a Blu-Ray than on a DVD. CSIT 301 (Blum) 64

Hard-coating technology • Blu-ray data is closer to the surface of the disc (compared to the DVD) – More vulnerable to scratches. – At first they came in cartridges for protection. – Newer polymer coating technology makes the cartridges unnecessary. CSIT 301 (Blum) 65

Recording speed CSIT 301 (Blum) 66

Region Codes CSIT 301 (Blum) 67

References • PC Hardware in a Nutshell, Thompson and Thompson • http: //www. pctechguide. com/10 dvd. htm • http: //www. webopedia. com • http: //www. pcguide. com • http: //entertainment. howstuffworks. com/cdburner 2. htm • http: //en. wikipedia. org/wiki/Blu-ray_Disc CSIT 301 (Blum) 68