The evolution of computer memory: from semiconductors to proteins
semiconductor memory
Conventional computer memory is known as “semiconductor memory” and was invented in 1968. It is based on a technology known as “semiconductor” which was invented in 1947. Many semiconductors grouped together are called “integrated circuit”, more commonly known as ” computer chips”. Examples of semiconductor memory include ROM, RAM, and flash memory. A great advantage of the RAM (main memory) of the computer is the price; ram is cheap. The main disadvantage of RAM memory is volatility; when you turn off your computer, the contents of RAM are lost.
molecular memory
Molecular memory is the name of a technology that uses organic molecules to store binary data. The Holy Grail of this technology would be to use a molecule to store a bit. For the near future, it would be more realistic to expect to have systems that use large groups of molecules to represent a single bit. Different types of molecules have been investigated, including protein molecules. A more precise name for a molecular memory system that uses protein molecules is Protein Memory. Other types of molecular memory would have more precise names derived from the types of molecules the technologies are based on.
protein memory
In the mid-1990s, the development of a protein-based memory system was the project of Robert Birge, professor of chemistry and director of the WM Keck Center for Molecular Electronics. He was assisted by Jeff Stuart, a biochemist and one of Birge’s graduate students. The protein molecule in question is called bacteriorhodospin. Purple in color, it exists in the halobacterium halobium microorganism that thrives in marshes where temperatures can reach 140F.
The protein undergoes a molecular change when exposed to light, making it ideal for displaying data. Each molecular change is part of a series of many different states known as a photocycle. There are three main states: the bR state, the OR state, and the Q state. The OR state binary represents 0 and the Q state represents binary 1, while the bR or quiescent state is neutral. To survive the harsh conditions of a salt marsh, the protein must be incredibly stable, a critical factor if it is to be used to represent data.
While in the bR state, the protein is placed in a clear container called a cuvette, which measures 1 x 1 x 2 inches. The container is then filled with a gel. The protein is fixed in place by solidification of the gel. 2 sets of lasers, one red and one green, are used to read and write data, while a blue laser is used for erasing.
Read, write and storage capacity
We will start in the bR state of the photocycle. A group of molecules is attacked and hit by the green laser array, also known as a paging laser. These molecules are now in the O state which represents binary 0. The OR state allows 2 possible actions:
• Reading: performed with the red laser array set to low intensity
• Write a binary 1: done with the red laser array set to high intensity that moves the molecules to the Q state
The Q state allows 2 possible actions:
• Reading: performed with the red laser array set to low intensity
• Erasing: done with the blue laser that makes the molecules return to the bR state
A bacteriorhodospin storage system is slow. Although the molecules change state in microseconds (millionths of a second), it is slow compared to semiconductor memory which has an access time measured in nanoseconds. Unfortunately, the time required to perform a read or write is even longer, on the order of ten milliseconds (thousandths of a second). The data transfer rate on this type of storage device is also very slow: 10 MBps (MB per second). In theory, the 1 x 1 x 2-inch bucket could hold 1 TB of data, or roughly a trillion bytes. In reality, Birge managed to store 800 MB and hoped to reach a capacity of 1.3 GB (one billion bytes). The technology was tested to the point that NASA was exploring methods to improve the technology during space shuttle missions, which actually resulted in higher storage densities.
conclusion
Birge’s quest to build a protein-based memory system for a desktop computer was unsuccessful. Although Birge’s vision failed, the development of some form of molecular memory (possibly protein memory) for desktop computers seems possible. Scientists have also continued to work on developing other ideas related to memory proteins. An idea from 2006 was to apply a layer of bR proteins to the surface of DVDs to increase storage capacity, theoretically up to 50 TB (more than 50 trillion bytes). A double-layer Blu-ray disc has a capacity of 50 GB (more than 50 billion bytes).