September 9, 1997
HITACHI DEVELOPS 4.7 GB DVD-RAM TECHNOLOGY
Hitachi, Ltd. today announced that it has developed
basic technologies for DVD-RAM (rewritable DVD) with
a capacity of 4.7 gigabytes(GB) per side, which was
achieved by implementing a recording medium with a
high signal to noise ratio (SNR) and a precise mark
recording strategy. The format based on 2.6 GB DVD-RAM,
which has already been agreed to as the unified DVD-RAM
format, ensures compatibility with the existing 2.6 GB
DVD-RAM and 4.7 GB DVD-ROM.
DVD is the acknowledged image and information storage
media of the next generation multimedia systems for video,
music, computers and a broad range of other applications.
Spurred by the introduction of DVD-Video for image
reproduction and DVD-ROM (read-only memory) for computers,
the market for DVDs has already taken off, and the DVD
family is being looked to as a united infrastructure for
image and information. Thus compatibility among DVD
formats is also essential for
the large capacity DVD-RAM.
Hitachi has been very active in the DVD business,
introducing the world's first DVD products. Hitachi has
been shipping single-speed DVD-ROM sample drives since
June 1996, double-speed DVD-ROM sample drives since March
1997, and DVD-RAM sample drives since June 1997.
Furthermore, Hitachi, the chair of the DVD-RAM working
group in the DVD forum, has greatly contributed to the
completion of the unified DVD-RAM format that takes users'
opinions into consideration.
The key concept for the 4.7 GB DVD-RAM technology is
large capacity without burden on the readout system.
The physical format (specifications for allocation of
information on the disc) is based on that of the 2.6 GB
DVD-RAM; with a reduced track pitch and bit pitch (*1).
The bit pitch, which has a major bearing on the readout
signal quality, was reduced to the same level as the
DVD-ROM. The track pitch was set narrower than that of
the DVD-ROM by making good use of the land and groove
structure.
The main features of the developed technology are as
follows.
(1)High-contrast media
High-contrast media greatly improves the readout signal
to noise ratio, resulting in high data reliability for
high density recording. Both high readout SNR and constant
thermal absorption are realized, which are important
for data overwriting. This resulted from the introduction
of a contrast enhancement layer (*2) and a thermal buffer
layer (*3).
(2)Adaptive recording waveform control
An adaptive recording waveform control method enabled
the accurate formation of recording marks much smaller
than optical spots.
The technologies developed made possible a 4.7 GB DVD-RAM
which is readable by any drive of the DVD family. Through
the developed technology, Hitachi will be contributing to
4.7 GB DVD-RAM format development activities, which start
this fall in the DVD forum.
Notes:
(*1) General Specifications for the DVD-RAM
| Items |
2.6 GB DVD-RAM |
4.7 GB DVD-RAM (This technology) |
4.7 GB DVD-ROM |
| Disc diameter |
120 mm |
<- |
<- |
| Substrate thickness |
0.6 mm x 2 |
<- |
<- |
| Recording layer |
Phase-change |
<- |
- |
| Laser wavelength |
650 nm |
<- |
650/ 635 nm |
| Lens numerical aperture |
0.6 |
<- |
<- |
| Bit length |
0.41 to 0.43 micrometers |
0.28 to 0.30 micrometers |
0.27 micrometers |
| Track pitch |
0.74 micrometers |
0.59 micrometers |
0.74 micrometers |
| Track format |
Wobbled Land & Groove |
<- |
A series of pits |
| Physical address |
Embossed pits |
<- |
<- |
| Recording code |
8 to 16, RLL(2,10) |
<- |
<- |
| Sector length |
2048 bytes |
<- |
<- |
| Error correction code (ECC) |
Reed-Solomon product code |
<- |
<- |
| ECC block length |
16 sectors |
<- |
<- |
| Sector allocation |
ZCLV |
<- |
CLV |
(*2) Contrast enhancement layer
A contrast enhancement layer improves the contrast
(difference between the reflectivity of recorded regions
and unrecorded regions) from 50% to 80 %, which is higher
than that of a DVD-ROM. This results in the high SNR
readout.
(*3) Thermal buffer layer
This layer keeps the thermal absorption in the recording
layer constant, independent of the recording marks before the
overwriting process, resulting in the accurate mark
formation. In phase change recording, the thermal control on
the media is a key to overwriting, since data is recorded by
utilizing the difference in cooling rates.
(*4) Adaptive recording waveform control
A method of controlling the form of the recording laser
pulse, the power and width of which are dynamically
controlled adaptive to the lengths of the recording mark
and the preceding and following spaces. This results
in a uniform thermal profile during the cooling process.
WRITTEN BY Secretary's Office
All Rights Reserved,
Copyright (C)
1997, Hitachi, Ltd.
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