Protein-Coated Disc is a theoretical optical disc technology currently being developed by Professor Venkatesan Renugopalakrishnan, formerly of Harvard Medical School

Harvard Medical School

Harvard Medical School is the graduate medical school of Harvard University. It is located in the Longwood Medical Area of the Mission Hill neighborhood of Boston, Massachusetts....

 and Florida International University

Florida International University

Florida International University is an American public research university in metropolitan Miami, Florida, in the United States, with its main campus in University Park...

. PCD would greatly increase storage over Holographic Versatile Disc

Holographic Versatile Disc

The Holographic Versatile Disc is an optical disc technology developed between April 2004 and mid-2008 that can store up to several terabytes of data on an optical disc the same size as a CD, DVD or Blu-ray disc. It employs a technique known as collinear holography, whereby a green and red laser...

 optical disc systems. It involves coating a normal DVD

DVD

A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

 with a special light-sensitive protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 made from a genetically altered microbe, which would in principle allow storage of up to 50 Terabyte

Terabyte

The terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...

s on one disc.
Working with the Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

ese NEC Corporation

NEC

, a Japanese multinational IT company, has its headquarters in Minato, Tokyo, Japan. NEC, part of the Sumitomo Group, provides information technology and network solutions to business enterprises, communications services providers and government....

, 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.

The technology uses the photosynthetic pigment bacteriorhodopsin

Bacteriorhodopsin

Bacteriorhodopsin is a protein used by Archaea, the most notable one being Halobacteria. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell...

 created from bacteria.
The information in such discs would be highly dense, due to being stored in proteins that are only a few nanometres across.