Multiple Users Utilizing a Single System
In business and enterprise computing, it is much more common to encounter systems with multiple simultaneous users. This is often because the computer and software being shared are more powerful and more costly than the typical consumer system. To maximize efficiency, a business might maintain a database on a single shared system. Multiple users can simultaneously access this system to add or retrieve data. These users might just as easily be other applications as well as humans.
For many years, multiuser operating systems like UNIX and Linux have enabled shar-ing of compute resources between multiple users. Each user gets a “slice” of the available compute resources. In this way, multicore systems provide more compute resources for the users to share.
Figure 3.3 illustrates the situation with multiple users of the same system. Multicore systems can be very well utilized running multiple applications, running
multiple copies of the same application, and supporting multiple simultaneous users. To the OS, these are all just multiple processes, and they will all benefit from the capabilities of a multicore system.
Multiuser operating systems enforce separation between the applications run by dif-ferent users. If a program one user was running were to cause other applications to crash or to write randomly to disk, the damage is limited to only those applications owned by that user or the disk space they have permission to change.
Such containment and security is critical for supporting multiple simultaneous users. As the number of users increases, so does the chance that one of them will do something that could “damage” the rest of the system. This could be something as simple as deleting critical files or enabling someone to get unauthorized access to the system.
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