Sony has been actively involved in the development of rewritable data disks, beginning with the 5.25-inch MO disk system (650MB) in 1988. Since then, Sony has doubled (1.3GB) the capacity in 1993, quadrupled it (2.6GB) in 1996, octupled it (5.2GB) in 1988, and is now working to develop 9.1GB system at 14 times the original capacity.

MO systems have gained popularity in the data storage market for features such as random access, high transfer rate, large capacity and long term reliability. In addition to PCs and workstations, MO systems are widely used to store data for LAN/Web servers and for storing medical image data and official public documents. In 1999, 120,000* units of the 5.25-inch MO system were shipped globally (Source: IDC report).


In anticipation of the ever-growing size of digital data in the network era, the market is now requesting an even higher capacity disk storage system with the 5.25-inch form factor. This is especially the case for data servers used for archival purposes, where large volumes of data must be quickly accessed and transferred.

In light of this market demand, Sony decided to develop the "5.25-inch UDO format," a next generation storage system based on a high density optical disk technology. By utilizing violet laser at 405nm wavelength and a land-groove recording system, the new format realizes 40GB of recording capacity. Dimensions of the external cartridge are the same as the current 5.25-inch MOs, which will facilitate future upgrades and expansions of the library systems. Sony is also developing a "Write Once Media Format" for archiving official public documents.

Sony will actively promote the "5.25-inch UDO format" as the optical disk storage system that offers a high capacity storage solution for data servers. In the future, development efforts will be undertaken to further increase the recording capacity to 80GB and 120GB.

Specifications of the "5.25 inch UDO Format"

	5.25-inch UDO Format		5.25-inch MO system (9.1GB)*under development
	Rewritable	Write-Once
Disk Diameter	130mm	130mm	130mm
Disk Thickness	2.4mm	2.4mm	2.4mm
Cartridge Size	Same as ISO 130mm (135 x 153 x 11 mm)	Same as ISO 130mm (135 x 153 x 11 mm)	ISO 130mm (135 x 153 x 11 mm)
Number of physical tracks	96,964	96,964	49,728
Sector size	8KB	8KB	4KB
Number of sectors	2,504,407	2,504,407	1,118,880
Data area	29.0-61.0mm	29.0-61.0mm	29.7-62.5mm
Laser wavelength	Violet (405nm)	Violet (405nm)	660nm
Objective lens (NA)	0.85	0.85	0.575
Recording layer	Phase change	Phase change	Magneto Optical
Recording format	Land & Groove	Land & Groove	Land & Groove
Recording side	both sides	both sides	both sides
Track Pitch	0.33um	0.33um	0.65um
Minimum bit length	0.13um	0.13um	0.3um
Recording density	15.0 Gb/inch2	15.0 Gb/inch2	3.3 Gb/inch2
Transfer rate	4-8MB/sec	4-8MB/sec	3-6MB/sec
Error correction	LDC	LDC	LDC
Modulation	RLL (1,7)	RLL (1,7)	RLL (1,7)