Introduction to Operating Systems

2 Introduction to Operating SystemsIf you are taking an undergraduate Operating Systems course, youshouldalready have some idea of what a computer program does when it not, this book (and the corresponding course) is going to be difficult so you should probably stop reading this book, or run to the near-est bookstore and quickly consume the necessary background materialbefore continuing (both Patt & Patel [PP03] and Bryant & O Hallaron[BOH10] are pretty great books).So what happens when a program runs?Well, a running program does one very simple thing: it executes in-structions. Many millions (and these days, even billions) of times ev-ery second, the processorfetchesan instruction from memory,decodesit ( , figures out which instruction this is), andexecutesit ( , it doesthe thing that it is supposed to do, like add two numbers together, accessmemory, check a condition, jump to a function, and so forth). Afterit isdone with this instruction, the processor moves on to the next instruction,and so on, and so on, until the program finally , we have just described the basics of theVon Neumannmodel ofcomputing2.

the how: what mechanisms and policies are implemented by the OS to attain virtualization? How does the OS do so efficiently? What hardware support is needed? We will use the “crux of the problem”, in shaded boxes such as this one, as a way to call out specific problems we are trying to solve in building an operating system.

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