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Holographic Storage

Hard drives have nearly been around for 50 years now and in that time the storage capacity has increased while the physical size decreased. Hard disk drives still have a spinning disc with a read and write head floating above it.

Holographic storage sounds like something from Star Wars, but it is actually an existing technology. It is an optical storage and it makes use of light to read and write the data. Similar to a CD and DVD in that regard, but where it differs is that the data is stored in three dimensions. The ability to store the data in multiple depths means that holographic storage offers high capacity.

In a standard hard disk drive, the platter needs to spin up and the head needs to move to where the data is. It is the same in an optical disc. However, it is different in holographic storage because everything is read in parallel. This means that there are increased data rates.

Holographic storage works by using two laser beams: a signal beam and a reference beam. The signal beam goes through a liquid crystal display, which then displays binary information. The beam then goes into a light sensitive polymer or crystal substrate. The reference beam comes from a different angle onto the substrate. The point where the two beams intersect creates an interference pattern, which is then used as a hologram.

The data is read by pointing the beams into the substrate at precisely the same angle as they were to make the data. This means that, through many different beam angles, that data can be stored in thousands of different layers. The data is then read by a Charged Couple Device.

A company called InPhase was one of the main developers of holographic storage, but their drive was huge and they were never able to meet the data transfer rates that they set out to achieve. They did produce a commercial holographic drive, but this used an optical disc system very similar in looks to a CD or DVD. It had 300 GB capacity but a frankly disappointing transfer rate of 20 MB/s. Perhaps tellingly, the company went bankrupt in October 2011.

One problem with holographic storage is that the speeds to write data to the system are very slow compared to the read speeds. As such, using it as a replacement for a hard drive isn’t really an option as you wouldn’t be able to access your data quickly. The technology is instead being fronted as an archival format; for companies that might need to store a lot of data it could be useful, since the life span is supposedly 50 years.

At the moment the technology is not close to where it needs to be to be marketed as a viable data storage solution. It may perhaps find a use for archiving, but even then recent developments in DNA as data storage seem far superior. The equipment may get smaller and with quicker access times, but it won’t be replacing hard drives or flash memory too soon.


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