Encyclopedia of Computer Science and Technology

monitor 317cities. After the mixing and combining is completed, separationand sequencing techniques can be used to find theshortest strand that includes all the cities. This representsthe solution to the problem.The attractiveness of molecular computing lies in itsbeing “massively parallel” (see multiprocessing). Althoughmolecular operations are individually much slower thanelectronics, DNA strands can be replicated and assembledin great numbers, potentially allowing them to go throughquintillions (10 18 ) of combinations at the same time. In1996, Dan Boneh designed an approach using DNA combinationsthat could be used to break the Data EncryptionStandard (DES) encryption scheme by testing huge numbersof keys simultaneously.In 2002 researchers at the Weizmann Institute of Sciencein Rehovot, Israel, announced that they had constructeda DNA computer that could perform 330 teraflops(trillions of operations per second). Two years later Weizmannresearchers described their new DNA computer,which could be used to diagnose and treat cancer on thecellular level.Although this application suggests the potential powerin molecular computing, the approach has significantdrawbacks. There are many ways that damage can occurto DNA strands during combination and processing, leadingto errors. Even for the combinatorial problems that aremolecular computing’s strong suit, conventional electroniccomputers using large arrays of parallel processors are ableto offer comparable power and a much easier interface.However, molecular computing illustrates the rich way inwhich information and information processing are embeddedin nature and the potential for harnessing it for practicalapplications.Further ReadingAmos, Martyn. Genesis Machines: The New Science of Biocomputing.New York: Overlook, 2008.———. Theoretical and Experimental DNA Computation. New York:Springer, 2005.———, ed. Cellular Computing. New York: Oxford UniversityPress, 2004.Calude, Christian, and Gheorghe Păun. Computing with Cells andAtoms: An Introduction to Quantum, DNA and Membrane Computing.New York: Routledge, 2001.Păun, Gheorghe, Grzegorz Rozenberg, and Arto Salomaa. DNAComputing: New Computing Paradigms. New York: Springer,1998.Ryu, Will. “DNA Computing: A Primer.” Ars Technica. Availableonline. URL: http://arstechnica.com/reviews/2q00/dna/dna-1.html. Accessed August 15, 2007.monitorAs designers strove to make computers more interactiveand user-friendly, the advantages of the cathode ray tube(CRT) already used in television became clear. Not onlycould text be displayed without wasting time and resourceson printing but the individually addressable dots (pixels)could be used to create graphics. While such displays wereused occasionally in defense and research systems in the1950s, the first widespread use of CRT video monitors camewith the new generation of smaller computers developedin the 1960s (see minicomputer). Since such computerswere often used for scientific, engineering, industrial control,and other real-time applications, the combination ofvideo display and keyboard (i.e., a Video Display Terminal,or VDT) was a much more practical way for users to overseethe activities of such systems. (This oversight function alsoled to the term monitor.)A monitor can be thought of as a television set thatreceives a converted digital signal rather than regular TVprogramming. To send an image to the screen, the PC firstassembles it in a memory area called a video buffer (modernvideo cards can store up to 64 MB of complex graphicsdata. See computer graphics). Ultimately, the graphics arestored as an array of memory locations that represent thecolors of the individual screen dots, or pixels. The videocard then sends this data through a digital to analog converter(DAC), which converts the data to a series of voltagelevels that are fed to the monitor.The monitor has electron “guns” that are aimedaccording to these voltages. (A monochrome monitor hasA standard computer monitor works much like an ordinary color TV set. The difference is that the signal is derived not from a broadcast program,but from the contents of video memory as processed and converted by the computer’s graphics card.