Protein Coated Disc A Remarkable Invention In The History Of Disc Technology

We know that it shouldn’t come as a shock anymore when researchers announce new storage technologies that promise to hold tantalizingly large amounts of data, but we were still pretty stoked to learn that a recent breakthrough at Harvard Medical School may eventually lead to DVD-size discs whose capacities approach an eye-popping 50TB. Unlike traditional optical or magnetic solutions, the disc developed by Professor V Renugopalakrishnan and his colleagues is coated with thousands of light-activated proteins called bacteriorhodopsin which are found in the membrane of a particular salt marsh microbe — and which temporarily convert to a series of intermediate molecules when exposed to sunlight.

Working with the Japanese NEC Corporation, Renugopalakrishnan’s team created a prototype device and estimated in July, 2006 that a USB disk would be commercialised in 12 months and a DVD in 18 to 24 months. However, no further information has been forthcoming since that time. The technology uses the photosynthetic pigment bacteriorhodopsin created from bacteria.

5 decades

Optical discs have been around for about 5 decades now and technologies around optical discs have been appearing ever since. Optical discs are very common today and play a vital role in storing all sorts of information digitally today. One of such optical disc technologies is the protein coated disc (PCD) technology which introduces optical discs with very high capacities. Here, optical discs are introduced, followed by the different generations of optical discs, then the protein coated discs in particular, the impact of PCD for ministry of defence (MOD), and then tries to conclude on PCD and how it may benefit the MOD.

What are optical discs?

In computing, an optical disc is a flat usually circular disc that acts as a storage medium for electronic data. Data is written to it and read from it using a laser beam or stamping machine. This is made possible by one or both of the surfaces of the discs being encoded with a special material. The encoding pattern on this surface follows a continuous, spiral path forming tracks that covering the entire disc. These tracks are further divided into sectors and contain the data stored in form of light and dark spots sometimes referred to as pits and lands.

The history of optical disc development is often referred to in reference to the different generations of optical discs. A generation normally refers to a timeline and the optical disc generations may be divided into four groups; the first, second, third and fourth. Each of the four generations is characterized by a major technological development that fundamentally changed the way they stored data. These different generations are looked at below.

First generation (1G) optical discs – The first generation of optical discs developed between the 1960s and 1980s comprised of Compact Discs (CDs), Laserdiscs (LDs) and Magneto-optical discs (MDs). The CD is 12cm in size, is able to hold 700mb of data, and was invented in 1965 by James Russell. The LD varies in size from 12cm till 20cm and is able to record 30 minutes or 60 minutes of video per side of the disc while the MD was invented in early 1980s and also varies in size. The MD 130mn (5.25 in) is able to hold 128 megabytes till 2.3 gigabytes and the MD 90mm (3.5 in) disks able to hold 650 MB till 16.7 GB.

Second generation (2G) optical discs – The second generation optical discs came after the first generation in the 90s and early 2000 and comprised of High capacity Mini Disc (Hi-MD), Digital Versatile Disc or Digital Video Disc (DVD), DVD-Audio, DualDisc, Digital Video Express (DIVX), Super Audio CD (SACD), Enhanced Versatile Disc (EVD), GD-ROM, Digital Multilayer Disk (DMD), DataPlay, Fluorescent Multilayer Disc (FMD), Phase-change Dual (PD) and Universal Media Disc (UMD).

Third generation (3G) optical discs – Third generation optical discs are currently being shipped (Blu-ray Disc (BD), High Definition DVD (HDDVD), and Professional Disc for DATA (PPD)) and in development (Forward Versatile Disc (FVD), Total HD disc, Versatile Multilayer Disc (VMD) and Ultra Density Optical (UDO)). 3G optical discs are meant for distributing high-definition video and support greater data storage capacities than 1G and 2G optical discs, accomplished with short-wavelength visible-light lasers and greater numerical apertures. The Blu-ray disc for example uses blue-violet lasers and focusing optics of greater aperture, for use with discs with smaller pits and lands. They can store from 25GB to 50GB of data.

Fourth generation (4G) optical discs – 4G optical discs are currently being researched and prototyped. They have the potential to hold more than 1TB of data. They currently comprise of; Tapestry Media, Holographic Versatile Disc (HVD) and Protein-Coated disc (PCD).

How 4G Optical discs are different

Over the years, optical storage density has been increased in the first 3 generations by shortening the wavelength of light used to read and write however fourth generation optical discs have deviated from the trend by not going in for shorter wavelength lasers but for a variety of large-capacity optical disc technologies including near-field recording, supper-resolution, recording, multilayer recording and holographic data storage. The following Protein Coated Disc (PCD) is the 4G optical discs technologies.

Protein Coated Disc (PCD)

PCD is a theoretical optical disc technology currently being developed. It entails covering a regular DVD with a special light-sensitive protein, which would in theory permit storage of up to 50 Terabytes on one disc. We are going to look at this technology in more detail in the next section.

How does it work?

This idea was presented at the International Conference on Nanoscience and Nanotechnology in Brisbane. Developed by Professor V. Renugopalakrishnan and colleagues, the protein coated disc technology unlike other optical technologies coats the disc with thousands of light activated proteins called bacteriorhodopsin (BR) which temporarily convert to a series of intermediate molecules when exposed to sun light and can withstand temperatures as high as 140C and pressures above 300GPa. This property allows the proteins to act as individual bits capable of representing or storing digital signals (1s and 0s) and ideal candidates for protein based building blocks for future electronic devices. However since the molecules have a tendency to return to their original state after a short period, Renugopalakrishnan and his colleagues have modified the required microbes’ DNA to create proteins capable of remaining in that intermediate state for several years. So if the ground state is taken to represent 0 and the intermediate taken to represent 1 and can be kept in this state for years then we have digital storage medium. The resultant protein based disc will have advantages over current optical storage technologies because data will be stored in proteins that are only a few nanometres (about 2nm) across. This is far smaller than the size of current pits and lands on discs today.

Possible benefits of PCD technology

With the demand for greater data density storage and memory devices growing exponentially, particularly with the ever-increasing use and explosive growth of broadband communication, Internet, increasingly complex multimedia mobile devices, and rapid expansion of on-demand databases serving multinational businesses PCD technology would benefit users and organizations alike if commercialized by allowing for a range of large capacity storage devices with unparallel data access rates. This seems obvious as one looks around at proposals and other technologies coming up for example standards for Ultra High Definition Television currently proposed by BBC, SH and RAI with data size of about 194GB/min.

Potentiality of PCD Technology

This technology was being developed and looked into by Renugopalakrishnan’s team and a Japanese corporation called NEC. NEC is a global company with a net income of about ¥110.267 billion. The PCD technology has the potential of recording higher densities and rates than other optical disc technologies, high durability against environmental conditions, high life-time for storage and by-passing the basic limit to the laws of scaling currently plaguing today’s storage technologies. It may also leap frog advances in electronics and could be used for devices for fast non destructive optical processing. With the potential of providing 2D protein based storage, it could relatively be cheaper than other 3D recording technologies that are usually more complex and bulky.

Feasibility of PCD Technology

With respect to feasibility, there is a possibility for cost-effective mass production through genetic engineering advances to increase the lifetime of the states (1 or 0). There also is the possibility of achieving data transfer rates of a few picoseconds. These data rates are far beyond the limits of competing technologies. There are also currently different ways to implement read and write mechanisms in protein disc recording and conventional methods employed to track the position of bits in today’s magnetic and optic drives could be used for the reading mechanism in protein coated discs. All these made this technology a feasible venture and it had a lot of positive feedback from the media, researchers and scientists. However, it is very less likely that the standards for today’s optical technology would suite PCD technology.

Challenges faced by PCD Technology

Despite what has been said so far, two main challenges face PCD implementation these are: the development of thin overcoats that would protect the protein films from environment and ensure adequate lifetime of the memory device; and the technology to provide adequate power in a Nano scale beam spot for read and writes. However, Renugopalakrishnan’s team and NEC have succeeded in creating a prototype for such a disc, they think it can be used for hard drives and USB drives for the future.


Still the concept is at the theoretical stage under the process of development but yes it is something which we cannot oversee or brush-off. Just imagine the time when this concept will turn into a reality we all would look at that disk and say “Oh God, proteins…!” The idea itself for the “Protein Coated Disks” excites us.

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