Encyclopedia of Computer Science and Technology

music, computer 325program’s priority would ordinarily entitle it to a greatershare of the CPU.Multitasking should be distinguished from two severalsimilar-sounding terms. Multitasking refers to entirely separateprograms taking turns executing on a single CPU.Multithreading, on the other hand, refers to separate piecesof code within a program executing simultaneously butsharing the program’s common memory space. Finally, multiprocessingor parallel processing refers to the use of morethan one CPU in a system, with each program or threadhaving its own CPU (see multiprocessing).Further ReadingSilberschatz, Abraham, Peter Baer Galvin, and Greg Gagne. OperatingSystem Concepts. 7th ed. New York: Wiley, 2004.Tanenbaum, Andrew S., and Albert S. Woodhull. Operating SystemsDesign and Implementation. 3rd ed. Upper Saddle River,N.J.: Prentice Hall, 2006.Windows users can bring up a window listing all processes or tasksrunning on the system, and shut down any task that has stoppedresponding to input.might be happening to the previous program. Thus, if a program“crashes,” the CPU will still be switched to the nextprogram, and the user can maintain control of the systemand shut down the offending program.Systems with preemptive multitasking often give programsor tasks different levels of priority that determinehow big a slice of CPU time they will get. For example, the“active” program (in Windows, the one whose window hasbeen selected for interaction by the user) will be given preferenceover a background program such as a print spooler.Also, the operating system can more intelligently assignCPU time according to what a given program is doing.Thus, if a program is waiting for user input, it may be givenonly an occasional slice of CPU time so it can check to seewhether input has been received. (The user, after all, ismillions of times slower than the CPU.) When some input(such as a menu selection) is ready for processing, the programcan be given higher priority.Priority can be expressed in two different ways. Oneway is to move a program up in the list of running tasks (seequeue). This ensures it gets a turn before any lower-prioritytask. The other way is to have turns of varying length, withthe higher-priority program getting a longer turn.Even operating systems with preemptive multitaskingcan provide facilities that programs can use to communicatetheir own sense of their priority. In UNIX systems,this is referred to as “niceness.” A “nice” program givesthe operating system permission to interrupt lengthy calculationsso other programs can have a turn, even if themusic, computerComputers have had a variety of effects on the performance,rendering, and composition of music. At the same time,the sound capabilities of standard personal computers haveimproved greatly, and music and other sounds have becomean integral part of games and educational software (seemultimedia).After the invention of the vacuum tube, a number of electronicinstruments were devised. The best known is the theremin,invented by Lev Termin, a Russian physicist, in 1919.The instrument consists of a vacuum tube connected to twoantennas. The player varies the pitch and volume of its eeriesound by moving his or her hands near the antennas.Some composers became fascinated by electronic music,both for its sense of modernity and its promise of breakingthe bonds of traditional form and instrumentation. In 1953,German composer Karlheinz Stockhausen (1928–2007)founded an Electronic Music Studio in Cologne and createdelectronic works.Meanwhile, inventors experimented with electronic synthesizerssuch as the RCA MKI and MKII, which used vacuumtubes and could be programmed with punched papertape. The advent of solid-state circuitry in the 1960s madesynthesizers far more reliable and compact. The Moog synthesizerin particular became a staple of leading-edge rockand avant-garde music. It was now time for the computer tocatch up to the potential of electronic sound.In the 1970s, digital music synthesizers with keyboardsand microprocessor-controlled sound generation becameavailable to adventurous (and fairly well-to-do) musicians.Ray Kurzweil’s digital music synthesis system, introducedin 1984, achieved a new level of sonic realism by usingprogramming stored in read-only memory (ROM) to emulatesubtle characteristics such as attack and timbre, realisticallyre-creating the sounds of many types of orchestralinstruments.Computer music synthesis enabled composers to experimentwith algorithmic composition. That is, they could useprograms to create new works by combining randomizationwith the permutation of patterns (serialism). Compositions