Information Technology Reference
In-Depth Information
this to work. How does the operating system enable multiple applications
to commmunicate with each other?
What if two users (or a million) try to request a web page from the server
at the same time? A simple approach might be to handle each request in
turn. If any individual request takes a long time, however, this approach
would mean that everyone else would need to wait for it to complete. A
faster, but more complex, solution is to multitask: to juggle the handling of
multiple requests at once. Multitasking is especially important on modern
multicore computers, as it provides a way to keep many processors busy.
How does the operating system enable applications to do multiple things
at once?
For better performance, the web server might want to keep a copy, some-
times called a cache, of recently requested pages, so that the next user to
request the same page can be returned the results from the cache, rather
than starting the request from scratch. This requires the application to
synchronize access to the cache's data structures by the thousands of web
requests being handled at the same time. How does the operating system
support application synchronization to shared data?
To customize and animate the user experience, it is common for web
servers to send clients scripting code, along with the contents of the web
page. But this means that clicking on a link can cause someone else's
code to run on your computer. How does the client operating system
protect itself from being compromised by a computer virus surreptitiously
embedded into the scripting code?
Suppose the web site administrator uses an editor to update the web page.
The web server needs to be able to read the file that the editor wrote; how
does the operating system store the bytes on disk so that later on the web
server can nd and read them?
Taking this a step further, the administrator probably wants to be able to
make a consistent set of changes to the web site, so that embedded links
are not left dangling, even temporarily. How can the operating system
enable users to make a set of changes to a web site, so that requests either
see the old pages or the new pages, but not a mishmash of the two?
What happens when the client browser and the web server run at different
speeds? If the server tries to send the web page to the client faster than
the client can draw the page, where are the contents of the file stored in
the meantime? Can the operating system decouple the client and server
so that each can run at its own speed, without slowing the other down?
As demand on the web server grows, the administrator is likely to want
to move to more powerful hardware, with more memory, more processors,
faster network devices, and faster disks.
To take advantage of this new
