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Modern Operating Systems by Herbert Bos and Andrew...
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Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 1056
SEC. 12.6
share the objects in a general way. Such a design would clearly lead to very dif-
ferent operating systems than we now have.
Another operating system issue that will have to be rethought with 64-bit ad-
dresses is virtual memory. With 2
bytes of virtual address space and 8-KB pages
we have 2
pages. Conventional page tables do not scale well to this size, so
something else is needed. Inverted page tables are a possibility, but other ideas
have been proposed as well (Talluri et al., 1995).
In any event there is plenty of
room for new research on 64-bit operating systems.
12.6.4 Seamless Data Access
Ever since the dawn of computing, there has been a strong distinction between
machine and
machine. If the data was on
machine, you could not ac-
cess it from
machine, unless you explicitly transferred it first. Similarly, even
if you had the data, you could not use it unless you had the right software installed.
This model is changing.
Nowadays, users expect much of the data to be accessible from anywhere at
any time. Typically, this is accomplished by storing the data in the cloud using stor-
age services like Dropbox, GoogleDrive, iCloud, and SkyDrive. All files stored
there can be accessed from any device that has a network connection. Moreover,
the programs to access the data often reside in the cloud too, so you do not even
have to have all the programs installed either. It allows people to read and modify
word-processor files, spreadsheets, and presentations using a smartphone on the
toilet. This is generally regarded as progress.
To make this happen seamlessly is tricky and requires a lot of clever systems’
solutions under the hood. For instance, what to do if there is no network con-
nection? Clearly, you do not want to stop people from working. Of course, you
could buffer changes locally and update the master document when the connection
was re-established, but what if multiple devices have made conflicting changes?
This is a very common problem if multiple users share data, but it could even hap-
pen with a single user. Moreover, if the file is large, you do not want to wait a long
time until you can access it. Caching, preloading and synchronization are key is-
sues here.
Current operating systems deal with merging multiple machines in a
seamful way (assuming that ‘‘seamful’’ is the opposite of ‘‘seamless’’) We can
surely do a lot better.
12.6.5 Battery-Powered Computers
Powerful PCs with 64-bit address spaces, high-bandwidth networking, multiple
processors, and high-quality audio and video, are now standard on desktop systems
and moving rapidly into notebooks, tablets, and even smartphones. As this trend

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