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Page 448
SEC. 5.7
and other things that used to require PC software. It is even possible that eventually
the only software people run on their PC is a Web browser, and maybe not even
It is probably a fair conclusion to say that most users want high-performance
interactive computing but do not really want to administer a computer. This has led
researchers to reexamine timesharing using dumb terminals (now politely called
thin clients
) that meet modern terminal expectations. X was a step in this direc-
tion and dedicated X terminals were popular for a little while but they fell out of
favor because they cost as much as PCs, could do less, and still needed some soft-
ware maintenance. The holy grail would be a high-performance interactive com-
puting system in which the user machines had no software at all. Interestingly
enough, this goal is achievable.
One of the best known thin clients is the
It is pushed actively
by Google, but with a wide variety of manufacturers providing a wide variety of
models. The notebook runs
which is based on Linux and the Chrome
Web browser and is assumed to be online all the time. Most other software is
hosted on the Web in the form of
Web Apps
, making the software stack on the
Chromebook itself considerably thinner than in most traditional notebooks. On the
other hand, a system that runs a full Linux stack, and a Chrome browser, it is not
exactly anorexic either.
The first general-purpose electronic computer, the ENIAC, had 18,000 vacuum
tubes and consumed 140,000 watts of power.
As a result, it ran up a nontrivial
electricity bill.
After the invention of the transistor, power usage dropped dramati-
cally and the computer industry lost interest in power requirements. However, now-
adays power management is back in the spotlight for several reasons, and the oper-
ating system is playing a role here.
Let us start with desktop PCs.
A desktop PC often has a 200-watt power sup-
ply (which is typically 85% efficient, that is, loses 15% of the incoming energy to
heat). If 100 million of these machines are turned on at once worldwide, together
they use 20,000 megawatts of electricity. This is the total output of 20 aver-
age-sized nuclear power plants.
If power requirements could be cut in half, we
could get rid of 10 nuclear power plants. From an environmental point of view, get-
ting rid of 10 nuclear power plants (or an equivalent number of fossil-fuel plants) is
a big win and well worth pursuing.
The other place where power is a big issue is on battery-powered computers,
including notebooks, handhelds, and Webpads, among others. The heart of the
problem is that the batteries cannot hold enough charge to last very long, a few
hours at most. Furthermore, despite massive research efforts by battery companies,
computer companies, and consumer electronics companies, progress is glacial.

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