Optical media options

Posted on July 01, 1999

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Optical media options

Richard A. Pollnow

The optical storage market includes a wide variety of formats. Here`s a quick rundown of the advantages and disadvantages of the major technologies.

MO 5.25-inch (ablative and CCW)

- Reads at 5MBps (maximum)

- Current capacity of 5.2GB per platter (dual-sided)

- Media life of >30 years

- Single-ended 10MBps SCSI interface

- ISO standard media format

Magneto-optical (MO) storage is portable, moderately fast, and durable. With decent random access speeds and a long media life, MO can be a good archive solution. The media is protected from outside magnetic radiation by a durable caddy.

MO is available in two WORM (Write-Once Read-Many) formats: ablative and CCW (Continuous Composite WORM). Ablative WORM physically changes the media so the recorded data cannot be altered. Using a hardware-based method, CCW WORM prevents data from being altered by disabling all erase and overwrite software functions.

MO is particularly suited to applications such as document imaging, hierarchical storage management (HSM), and archiving, or any application that requires WORM media and random access.

The list price for a 5.2GB platter is about $95, or 1.83 cents per MB.

Optical 12-inch (WORM)

- Reads at 2.7MBps (maximum)

- Highest storage capacity of 12GB per platter (dual-sided)

- Media life of >30 years

- Single-ended 10MBps SCSI interface

- Media is not an ISO standard; drives and media from different vendors are incompatible

Optical 12-inch media has the same attributes as 5.25-inch optical except that it is ablative WORM only. Once written, the media cannot be altered.

Although 12-inch optical has a slower transfer rate than 5.25-inch MO, its time-to-data rate is faster since a large amount of data is under the heads at all times. In addition, the drives have two heads, allowing simultaneous access to both sides of the platter. This configuration puts 12GB of data under the heads in each drive.

The price for a 12GB disc is about $525, or 4.38 cents per MB. Although this is relatively expensive for an optical solution, it is the only technology that meets certain governmental and legal requirements for document security.

A new version of 12-inch optical is due this fall, with a capacity of 30GB per platter and a read speed of 6.2MBps. The price for media will be approximately $595, or 1.98 cents per MB.

120mm (CD-ROM, CD-R, CD-RW)

- Requires "authoring software," and data usually needs to be staged before it is written

- Media life >30 years

- Current 40X reads at up to 6MBps

- Capacity of only 650MB on single-sided media

- Single-ended 10MBps SCSI interface

CD technology is widespread and standardized. The media is inexpensive, easily transported, and impervious to outside magnetic forces. CD-R can only be written to once. CD-RW media can be written to multiple times, but is much more expensive.

CD`s main disadvantage lies in its operational complexities. This is changing, though, as software programs increasingly use drag-and-drop methods. Secondly, at 640MB, CD has a low capacity per disc. Despite this drawback, CD is often used as an archive solution.

Writable CD technologies are available in two main formats: CD-R and CD-RW. CD-R is essentially a WORM media; it cannot be altered once it has been written. For this reason, CD-R is often used in archive applications. Also, at about a dollar a disk (0.154 cents per MB), CD-R media is one of the most affordable options.

CD-RW, on the other hand, can be rewritten and used for quick reusable backup. However, the media is still relatively expensive at around $17 per disc. Currently, CD-RW has reached only 4X speed, while CD-R is up to 8X speed.

120mm (DVD)

- More than one format (standards in dispute)

- 2.6GB on single-sided DVD-RAM media

- 5.2GB on double-sided DVD-RAM media

- 4.7GB on single-sided DVD-R media

- Media life >30 years

- DVD-RAM sustained read speed >1MBps

- DVD-RAM read of DVD-ROM media approximately 2.76MBps

- DVD-RAM media is transportable and impervious to extraneous magnetic interference. It has a low cost-per-MB (0.96 cents) and can store a large amount of data in a small space. Unfortunately, the media is slow (1MBps) and DVD standards are still under dispute.

DVD-RAM drives can read all forms of CD media; backward compatibility is one of DVD-RAM`s main advantages.

Currently, most library manufacturers are planning to use single-sided 2.6GB DVD-RAM media. Although double-sided media is more efficient, it requires a flipping mechanism not currently available. As speeds and capacities increase, DVD-RAM will compete more directly with MO and other optical formats.

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Richard A. Pollnow is an applications engineer at Plasmon IDE, in Minneapolis. www.plasmon.com.


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