Definition

optical storage

Contributor(s): Rodney Brown

Optical storage is any storage type in which data is written and read with a laser. Typically, data is written to optical media, such as compact discs (CDs) and DVDs. Initially targeted as a potential replacement for hard disk drives (HDDs) in computing systems, the lack of growth in capacity compared to both hard disk and later solid-state flash storage has relegated optical storage use mostly to long-term archiving and data backup.

Optical media is more durable than tape, HDDs and flash drives and less vulnerable to environmental conditions. However, it tends to be slower than typical HDD speeds and offers lower storage capacities. According to the Optical Storage Technology Association (OSTA), current optical speeds are approaching those of HDDs.

The current standard optical format is Blu-ray, which uses a blue laser to dramatically increase capacities.

History

The first method for storing data using light on a hard medium was invented by James T. Russell in the late 1960s.

Russell's creation bears little resemblance to current optical storage technology. His invention used micron-sized dots of light and dark to indicate the presence or absence of a digital bit. That pattern was read by having light pass through the otherwise transparent medium it was encoded on.

Modern optical storage discs started with the CD format released by Philips and Sony in 1982. In contrast to Russell's system, these modern discs use a laser to create pits on a reflective surface, such as aluminum foil under a hard transparent plastic covering. The size of the pit is determined by the wavelength of the laser light.

optical storage media formats
A variety of optical storage disc formats

Because the blue light laser used with Blu-ray discs is short in wavelength, 27 gigabytes of storage can be encoded on a single-sided, 12-centimeter disc. That's up from 680 megabytes for the original CD and 4.7 GB for the DVD. That makes Blu-ray the current standard in optical disc storage.

The development of greater optical storage capacity, while slower than that of HDD or solid-state drives, hasn't stopped. In 2016, Sony announced a Blu-ray disc that can hold up to 3.3 terabytes of data.

Advantages/disadvantages

Optical storage has one major advantage over magnetic storage: durability. Optical discs are not vulnerable to data loss due to power failure like volatile memory; not as subject to wear like most non-volatile memory, such as flash; and much more physically sturdy than magnetic tape, which is the leading archival storage medium.

Another advantage of optical disc is that the storage medium is inexpensive to manufacture. The materials are mainly aluminum foil and plastic.

To take full advantage of the low manufacturing cost of optical discs requires bulk production of discs containing the same data, as in the case of a Blu-ray movie or audio CD. This is done using a die and stamp technique that presses the tiny dots into the reflective foil medium in an assembly line process.

Optical discs for storage needs to be rewritable, unlike those used for movies that are written to once, which changes the material used in the disc. Instead of using a low-cost reflective foil layer -- like with rewritable discs -- the dots are written into a more expensive layer of phase-change material that enables the data to be erased and written over multiple times.

The biggest disadvantage of optical storage is disk capacity. Currently topping out at 27 GB for a 12-centimeter Blu-ray Disc, flash storage has that capacity beat handily on a per-centimeter basis. While Sony is developing a 3.3 TB Blu-ray Disc, IT administrators can currently purchase an enterprise-grade 10 TB HDD.

This was last updated in November 2018

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