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DVD Technical Guide 7-DVD-RAM

05/27/2008 04:25:16

Chapter 1 DVD Overview

Chapter 7 DVD-RAM

7.1 Background of the DVD-RAM Specification

With the increasing performance of PCs in recent years, there has also been a dramatic increase in the quantity of data they handle. This increase is expected to continue with the increase in video usage, the move to broadband, and the increase in multimedia applications. Along with the increasing capacities of hard disks to store this data, there has also been increasing demand for high-capacity rewritable storage media. Users and computer makers have said they want a rewritable disc which is compatible with ROM discs. The rewritable disc DVD-RAM specification was created to meet these requests.
Rewritable disc technologies currently on the market include magneto-optical (MO) and phase-change. Magneto-optical discs work by using laser light and an external magnetic field to record data in changing directions of magnetic regions on the disc. Discs in use today include 130 mm and 90 mm diameter data discs, 300 mm diameter video file discs, and MiniDiscs for recording music. These discs use a signal detection method involving rotation of a polarizing plane via the magneto-optical effect.
Phase change technology, on the other hand, utilize the ability of laser light to change the recording material from a crystalline to an amorphous state, and back again. A pulse of high-power laser light heats the recording surface to above the melting point, and the material is cooled quickly to cause it to enter an amorphous state. On the other hand, an amorphous region can be heated by medium-power laser light to above the temperature for crystallization to cause it to enter a crystalline state. The signal is encoded in the difference in reflectivity due to the different optical indices of the amorphous and crystalline regions. This technology was later coming to market than magneto-optical, due to the effort required to develop sufficient rewrite durability, but 120 mm and 130 mm diameter data discs and associated hardware are available today.

Phase change technology was chosen for DVD-RAM for the following reasons.

  1. The use of changing reflectivity to reproduce the signal makes it easy to achieve compatibility with read-only players.
  2. The use of laser power modulation makes it easy to achieve direct overwrite capability.
  3. The optical system is simpler than the magneto-optical system required to detect rotated polarized surfaces, and there is no need for a magnetic head to apply the external magnetic field.
  4. A relatively large signal can be obtained even from the smaller recording marks resulting from increasing disc density, and the technology can also be made compatible with shorter wavelength blue light that is anticipated for future use. 

7.2 2.6 GB DVD-RAM Specifications

 

Recording media phase change disc
disc dimensions 120 mm diameter, bonded 0.6 mm thick substrates
laser wavelength, NA 650nm, 0.6
modulation method 8/16 encoding
sector size 2kB
ECC block size 32kB
error correction method RSPC
capacity 2.6 GB (one sided)
disc format ZCLV (Zoned Constant Linear Velocity)
number of data area zones 24zone
addressing method CAPA (Complimentary Allocated Pit Addressing)
recording bit length 0.41m/bit
recording method mark edge recording
track pitch 0.74m, land and groove
tracking method push-pull
file system UDF
user data rate 11.08Mbps
Table 1 Basic Specifications of DVD-RAM version 1.0

 

 

Table 1 shows the basic specifications of the DVD-RAM specification version 1.0. These specifications achieve the key goals of compatibility with DVD-ROM discs and a large capacity of 2.6 GB per side.
The disc dimensions are the same as for DVD-ROM, with discs 120 mm in diameter composed of bonded 0.6 mm thick substrates, and the standard pickup also has a wavelength of 650 nm and a numerical aperture of 0.6.
Further, the encoding method, sector size, ECC block size, and error correction method were specified to be 8/16 encoding, 2 kB, 32 kB, and Reed-Solomon Product Code; these are all the same as DVD-ROM, to facilitate compatibility with DVD-ROM players.
The data rate is also the same as DVD-ROM, at over 11 Mbps. The file system was also specified for compatibility with ROM, as DVD-RAM uses the Universal Disc Format (UDF) defined by the Optical Storage Technology Association (OSTA). This file system is designed to support both the random access needed for data file applications, and the sequential access needed for video recording.

7.3 4.7 GB DVD-RAM Format

 

Recording media phase change disc
disc dimensions 120 mm diameter, bonded 0.6 mm thick substrates
laser wavelength, NA 650nm, 0.6
modulation method 8/16 encoding
sector size 2kB
ECC block size 32kB
error correction method RSPC
capacity 4.7 GB (one sided)
disc format ZCLV
number of data area zones 35zone
addressing method CAPA (Complimentary Allocated Pit Addressing)
recording bit length 0.28m/bit
recording method mark edge recording
track pitch 0.615 m,   land and groove
tracking method push-pull
file system UDF
user data rate 22.16Mbps
Table 1 Basic Specifications of DVD-RAM version 2.0
(changes from version 1.0 highlighted with bold text)

 After the release of the DVD-RAM version 1.0 specification, version 2.0 for 4.7 GB discs was created. The major differences between version 1.0 and version 2.0 are given below.

  1. 4.7 GB capacity
    Version 2.0 increases the capacity of a single disc side from 2.6 GB to 4.7 GB, the same as for DVD-ROM. This was accomplished by decreasing track pitch from 0.74 m to 0.615m and recording bit length from 0.41 m/bit to 0.28 m/bit.
  2. 22.16 Mbps standard data rate
    VThe data rate of version 1.0 is the same as DVD-ROM, at 11.08 Mbps. Version 2.0 doubles the standard data rate to 22.18 Mbps to improve data recording capability.
  3. Defect management method
    Version 2.0 incorporates a new defect management method to support real-time recording of audio and video data.


7.4 1.46 GB (8 cm) DVD-RAM Format

 

Recording media phase change disc
disc dimensions 80 mm diameter, bonded 0.6 mm thick substrates
laser wavelength, NA 650nm, 0.6
modulation method 8/16 encoding
sector size 2kB
ECC block size 32kB
error correction method RSPC
capacity 1.46 GB (one sided)
disc format ZCLV
number of data area zones 14zone
addressing method CAPA (Complimentary Allocated Pit Addressing)
recording bit length 0.28m/bit
recording method mark edge recording
track pitch 0.615 m, land and groove
tracking method push-pull
file system UDF
user data rate 22.16Mbps
Table 1 Basic Specifications of the DVD-RAM 8 cm Specification
(changes from version 2.0 12 cm specification highlighted with bold text)

 

 

 

The DVD-RAM version 2.1 specification was based on the 4.7 GB DVD-RAM version 2.0 specification to define an 8 cm disc. The major differences between the 8 cm disc and the 4.7 GB, 12 cm disc are as follows.

  1. 8 cm diameter
    The disc size was reduced from 12 cm to 8 cm. In addition, an 8 cm case is also provided.
  2. 1.46 GB capacity
    The recording capacity dropped from 4.7 GB to 1.46 GB as a result of the decrease in size. The track pitch is 0.615 m, and the recording bit length is 0.28 m/bit, the same as with the 4.7 GB disc.
  3. 14 zones
    The number of zones was reduced from 41 in the 4.7 GB disc to 14.

All the remaining specifications are the same as for the 4.7 GB disc.

 

7.5 Land and Groove Format

 

 

 

 

 

 

 The figure above shows a typical DVD-RAM structure. A DVD-RAM disc holds 2.6 GB per side (5.2 GB for both sides), or 4.7 GB (9.4 GB for both sides). This high recording density was achieved through the use of mark edge recording, along with the use of land and groove recording, which is effective for use with narrow track pitches. Previous optical discs used continuous groove recording, in which data is recorded only within the tracking grooves. Land and groove recording increases recording density by writing data both in the grooves and on the lands between the grooves. There is a limit to how much track pitch can be reduced as a means of increasing recording density, as narrow track pitch tends to weaken the tracking servo signal and increase crosstalk. The solution is land and groove recording. In phase change discs the groove depth is designed to be /6n, where is the pickup laser wavelength and n is the optical index of the substrate. This reduces crosstalk between the lands and the grooves, and allows conventional tracking signal schemes to be used with narrow track pitches.
The reduction in crosstalk with the land and groove method is a result of the fact that the reduction in reflected light due to interference with a neighboring track when in crystalline state is approximately the same as decrease in reflectivity when in amorphous state at a particular depth. That depth is about /6n, which is about 70 nm for a 650 nm laser wavelength.
DVD-RAM uses this kind of land and groove recording, with a track pitch of 0.74 m (the same as in DVD-ROM) in the 2.6 GB version 1.0, and 0.615 m in the 4.7 GB version 2.0.


7.6 CAPA (Complimentary Allocated Pit Addressing)

 

 

 

 

 

 The address signal uses a method called CAPA (Complimentary Allocated Pit Addressing) as a Physical ID (PID), and is recorded once per sector. In CAPA, the pits which record the PID are offset by one-half track from the data recording track (land or groove), to form a structure like that shown in the figure above. When groove tracking the address may be obtained from the CAPA signal behind, and when land tracking the address is obtained from the CAPA signal ahead. In each zone, the CAPA is aligned radially to allow CAV operation. The data recording area (land or groove) between each CAPA header is wobbled. Counting the number of wobbles allows the drive to accurately know the position of the next CAPA header.

7.7 Sectors

 

 

 

 

   

Sectors are comprised of CAPA headers, where the address is recorded using embossed pits, and a data recording area on a land or in a groove. The data recording area has a structure as shown in the figure above. Reading is performed by extracting the clock in the VFO area and determining a binary slice level. The PS field allows detection of the start point, and data is read. This data area contains one DVD-ROM sector of data. The buffer areas ahead and behind are there to prevent influence on data reading due to degradation of the recording layer. Further, to help prevent surface degradation, the recording position is moved about at random, to prevent degradation of the recording layer at any particular point.
Sixteen sectors of data make up one ECC block, with error correction performed on the entire block.


7.8 ZCLV (Zoned Constant Linear Velocity) Format

 

  
Figure 1 2.6 GB DVD-RAM Zone Structure
(The structures of 4.7 GB and 1.46 GB, 8 cm discs are essentially the same, with the exception of the number of zones.)

The ZCLV (Zoned Constant Linear Velocity) method divides the disc into regions with different numbers of sectors, based on radial distance. This method provides for recording at a constant data rate via zone-based rotational control, and provides high recording density and easy rotational control and signal processing.
A version 1.0 2.6 GB disc is divided into 24 zones, with 17 sectors per rotation in the innermost zone, and 41 sectors per rotation in the outermost zone.
As shown in Figure 1, a DVD-RAM is divided into a lead-in area, a data area, and a lead-out area. The lead-in area is divided into an embossed pit area and a rewritable area. The embossed pit area contains control data such as the disc type, format, and recording method. The rewritable portion of the lead-in area use used for disc or drive testing, data for processing defects in a disc, etc.

 

Chapter 2 Physical Format of Read-Only Discs

Chapter 3 Read-Only Disc File Format

Chapter 4 Video Format

Chapter 5 Audio Format

Chapter 6 DVD-R and DVD-RW

Chapter 7 DVD-RAM

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