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Cloud Software
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Figure1.5: Cloud computing
{ Glue. Cloud services often distribute their work across dierent ma-
chines. What abstractions should the cloud software provide to help
services coordinate and share data between their various activities?
Web browsers (Figure 1.6) such as Chrome, Internet Explorer, Firefox, and
Safari each play a role similar to an operating system. Browsers load and
display web pages, but as we mentioned earlier, many web pages embed
scripting programs that the browser must execute. These scripts are often
buggy and sometimes malicious; hackers have used them to take over vast
numbers of home computers. Like an operating system, the browser must
isolate the user, other web sites, and even the browser itself from errors
or malicious activity by these scripts. Similarly, most browsers have a
plug-in architecture for supporting extensions, and these extensions also
need to be isolated from causing harm.
{ Referee. How can a browser ensure responsiveness, when a user has
multiple tabs open and each tab is running a script from a different
web site? How can we sandbox web scripts and plug-ins to prevent
bugs from crashing the browser, and to prevent malicious scripts from
accessing sensitive user data?
{ Illusionist. Many web services are geographically distributed for
better fault tolerance. This way, if one server crashes or if its net-
work connection has problems, the browser can connect to a different
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