(Origina l Sony page)
                                          1996 / 12 / 16 


Technology / Research and Development

A data use MD has been developed that provides a 650 megabyte memory capacity, enlarging the MD data standard's designed capacity through a 4X increase in density.

Left: 4X Density MD, enlarged surface image.
Right: Current Data MD,enlarged surface image.

Sony has developed a 4X density MD, which realizes a memory capacity of 650MB through the use of a data media providing small size, large capacity and excellent portability.

Due to MD's characteristic high sound quality and quick access, the audio MD market is currently growing, through wider use in applications ranging from portable use to car audio use. Furthermore, MD data (memory capacity 140MB), standardized in 1993, has seen increasing use in areas such as document archiving, using the Sony "Data Eater" personal MD file, as well as in home and office information appliances.

The new "4X density MD" realizes a factor of 4.6 increase in memory capacity to 650MB by pursuing a densification of the current MD data format. This densification has been achieved using new techniques such as laser strobe magnetic modulation technology, high density magnetic film technology, and a miniaturization of the beam spot by reducing the wavelength of the record / playback laser and increasing the numerical aperture of the lens. Through the establishment of this new technology, it has become possible to freely conduct the recording and playback of still and motion video images on a compact MD media holding the CD-ROM equivalent of 650 MB of information.

Henceforth, we plan in the spring of 1997, based on this technology, to establish a standard together with Sharp Corp., from whom we have received participation in the development of this technology, and then call extensively upon other industry firms to adopt this technology.

Main Technology Summary
1. Beam Spot Reduction
By both reducing the recording and playback laser's wavelength to 650 nanometers (presently 780nm), and enlarging the numerical aperture of the lens to 0.52 (presently 0.45) a reduction in beam spot size has been realized. By way of this, signals recorded at a track pitch of 0.9um can be accurately read.

2. Laser Strobe Magnetic Modulation Technology
During the time when the recording magnet is being modulated, timing is set by pulsing the laser light. Doing this, inter- (intra-?) track interference is reduced, and it is possible to realize wide recording margins.

3. High Density Magnetic Film Technology
Corresponding to the increase in density, an optimizaton of the the groove shape, as well as the magnetic film, has been carried out. A high S/N has been achieved.

4. Signal Processing Technology
Partial response, compound viterbi, digital equalization, etc. technology has been employed, resulting in an improved reproduction ability, and even though the recording density has been increased, stable readout is made possible.

5. High Transfer Rate
Through the development of high data transfer rate technology, it has even become possible to record MPEG2 level data, making possible its use in various image applications.

6. Compatability with present MD Data
By making the disc the same 1.2mm size as the current MD data it is possible to unify the optical system, in a system in which 4X density MD has been adopted, the ability to record and playback current MD data discs is being considered.


Memory Capacity 650MB
Data Transfer Rate 580kB/s
Sector Size 2048B
Recording Data Unit 32kB
Cartridge Dimensions 68 X 72 X 5mm
Disc Diameter 64mm
Disc Thickness 1.2mm
Track Pitch 0.9um
Laser Wavelength 650nm
Lens Numerical Aperture 0.52
Recording Method Magnetic Modulation Direct Overwrite
Disc Linear Velocity 2.05m/s
Signal Encoding Method RLL(1, 7)
Error Correction Method Reed Solomon Code


Regarding the present MD Data Standard

(Standard Completed 1993/7)
Memory Capacity140MB
Data Transfer Rate150kB/s
Sector Size 2048B
Recording Data Unit64kB
Cartridge Size68 X 72 X 5mm
Disc Diameter 64mm
Disc Thickness1.2mm
Track Pitch1.6um
Laser Wavelength780nm
Lens Numerical Aperture 0.45
Recording MethodMagnetic Modulation Direct Overwrite
Disc Linear Velocity1.2m/s
Signal Encoding Method EFM
Error Correction MethodACIRC

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