Second generation computers did not have the necessary hardware to protectthe operating system from malicious user programs.Ħ. A CPU could do other work if the I/O were slowfor other reasons (arriving on a serial line, for instance).ĥ. This of course assumes the major delay is thewait while data are copied. No matter how much I/O a program does, theCPU will be 100 percent busy. If there is no DMA, the CPU is fully occu-pied doing I/O, so there is nothing to be gained (at least in terms of CPU utili-zation) by multiprogramming.
The prime reason for multiprogramming is to give the CPU something to dowhile waiting for I/O to complete. Input spooling on a personal computer isnot very likely, but output spooling is.Ĥ. Output spooling consists of firstcopying printable files to disk before printing them, rather than printingdirectly as the output is generated. Input spooling is the technique of reading in jobs, for example, from cards,onto the disk, so that when the currently executing processes are finished,there will be work waiting for the CPU. It is commonly used to keep the CPU busy while oneor more processes are doing I/O.ģ. Multiprogramming is the rapid switching of the CPU between multipleprocesses in memory. An operating system must provide the users with an extended (i.e., virtual)machine, and it must manage the I/O devices and other system resources.Ģ. Vrije UniversiteitAmsterdam, The Netherlandsġ.
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