Optical disc technology now spans the range from simple workstation storage to advanced enterprise-level image storage systems. Once limited to a small number of relatively stable formats, it has recently blossomed into a diverse range of form factors and standards designed to take advantage of new technologies. The 3.5in, 5.25in and 120mm formats are still there, but there have been radical changes in how data is stored, particularly with multi-layer systems and phase change technology. This is particularly noticeable in the 120mm area, due to the need to maintain compatibility with previous systems.
In the 120 mm (CD) world, there is a diverse collection of standards for writable media. DVD-ROM is the standard bearer in the read-only world, so much of the attention is being focused on DVD variants.
These include DVD-RAM and DVD+RW (DVD ReWritable). DVD-RAM is the rewritable DVD standard finalised and published by the DVD Forum. The 1.0 specification (a phase-change design) can hold 2.6GB of data per side on single- or double-sided discs. DVD+RW is a new rewritable DVD format offering larger capacities that has not yet been standardised.
DVD+RW uses single-layer phase-change discs that provide 3GB per side. Pioneer has its own specification, called DVD-R/W. This is based on CD-RW and uses random-access media to hold up to 3.95GB. NEC's Multimedia Video File format (MMVF) is another contender. It provides 5.2GB capacity on one side, and should be available before the end of the year.
Phase-Change Dual (PD) 650MB drives from NEC, Panasonic, and Toray read and write to a rewritable 120mm disc encased in a cartridge, like DVD-RAM, and you can read and write PD discs in 2.6GB DVD-RAM drives.
In the non-DVD categories, there are standard-format 5.25in Magnetic-Optical (MO) drives, offering 2.6GB per double-sided disc or 1.3GB online and Pinnacle Micro's proprietary-format Apex 4.6GB MO drive, with 2.3GB online. Lower capacity 3.5in MO format drives are also available, with 1.3GB drives due out this year also capable of reading and writing older 230MB and 640MB MO discs.
Lack of compatibility
If you thought that all of these different formats might make compatibility difficult, you would certainly be correct. First, of course, there is little to no compatibility across form factors -120mm, 3.5in and 5.25in. Within form factors - and here, we are mainly concerned with the 120mm CDs - compatibility is iffy at best.
One issue that brought standards to the fore was the inability of first generation DVD-ROM devices to read CD-R media. The result was marketplace confusion, delays in DVD acceptance, and a loss of consumer confidence. Next generation DVD-ROM drives incorporated a dual wavelength optical head to maintain read compatibility with previously recorded CD-R and CD-RW discs. But the damage had already been done, and industry standards once again came to the fore.
A movement aimed at straightening out these differences comes from the Optical Storage Technology Association (OSTA) which has proposed MultiRead, an optical-drive specification ratified by members in July 1997. MultiRead enables CD-Audio, CD-ROM, CD-R and CD-RW discs to be read on current and future CD and DVD devices. The 31 vendors seeking applications for use of the specification represent 98 per cent of CD and DVD optical-drive shipments worldwide.
Meanwhile, specifications for the Advanced Storage-Magneto Optical (AS-M-O) disc system, a 120mm diameter 6GB M-O system seen as a potential rival to DVD-RAM, have also been announced by the OSTA. The 120mm diameter gives AS-MO sufficient compatibility with DVD-ROM for a chance to emerge as a rewritable medium. Sixteen companies have announced support for AS-MO, but none have yet disclosed marketing plans for AS-MO products. TeraStor also has a 20GB MO disc system based on Near Field Recording (NFR) in development. The company is now working with Quantum to release a product in 1999 that will compete mainly in the high-end markets.
While attention has turned to the DVD area and compatibility issues within the 120mm format, each of these technologies has a growth path. DVD-RAM and its variants are expected to reach 4.7GB per side by mid 1999, according to the OSTA. In the same time period, the 3.5in (90mm) format is expected to reach 2 to 4MB, while 5.25 media are expected to pass 5.2GB. In cost and popularity, the 120mm format will continue to lead the way, with 5.25in following as a large capacity format. The small, 3.5in discs have failed to catch on in the US, and this will tend to keep them in the background and reduce price advantages. The 5.25in disc appears to have a secure future as a large-scale storage system for enterprise level networks.
Optical disc capacity can also be extended in the same manner as tape and hard disk storage - by providing disc libraries and towers capable of handling multiple optical discs and bringing storage to the multiple terabyte level. These devices have been available for some time with magneto-optical storage as an enterprise level solution. They are now becoming available for the newer and less expensive 120mm CD forms.