Transcript A Novel Concurrency Control Algorithm in Distributed Groupware

The Computer for the 21st Century
Mark Weiser – XEROX PARC
Presented By: Mihail Ionescu
Outline
• Brief presentation of the paper
• What happened in these 10 years in this
domain since the paper was published
• Conclusions
Motivation
• The best technologies are those that
disappear.
• Writing is the best example  it is almost
invisible for us in the sense that it is used
almost without realizing it.
• Possessing the most powerful computer is
like having just one book, does not matter
how big it is.
• Also, the computer screen demands full
attention.
Contributions
• Not real technical contributions, since it is not a
technical paper.
• One of the first (if not The first) papers that try
argue for the need that the silicon technology
should “vanish in the background”.
• Some real life scenarios of using this paradigm.
• Identity the technical requirements of an
infrastructure for supporting the ubiquitous
computing.
Ubiquitous Computing
• The computers will be everywhere: pens, cans,
pads, boards, coffee machines, alarm watches, etc.
• Some of the devices (like traffic lights, ovens, etc.)
already have computers incorporated, but without
the possibility of communicating between each
other, which is very important.
• At least hundreds of components in each room.
• Electronic badges are already in use (I think).
• Current prototypes to build pads, tabs.
Technical Requirements
• Three main parts
– Cheap, low-power computers that include
convenient displays
– A network to tie them together
– Software systems to implement ubiquitous
applications
Low-power Computers
• The first requirement is not so difficult to be met
• Even at the time when the paper was written such
devices existed
• Today there are such devices with processors of
200 MHz (maybe more), RAM of 128 M and even
color displays
• The devices should be simple, no AI or other
complex technologies
Network
• Data transmission rates for both wired and
wireless networks are increasing.
• The current systems cannot (and will not) support
hundreds of machines per room.
• Three types of network connections: tiny range
wireless, long range wireless and very high speed
wired  it is a need of a single kind of network
connection that somehow serve all three functions.
Applications
• New operating system idea that does not assume a
relatively fixed configuration of hardware and
software.
• New systems that have to deal with the diversity
of inputs from the user.
What Happened in 10 Years
• Almost nothing that was described in the
paper (even if Weiser predicted 20 years).
• The devices are here, maybe more powerful
that Weiser imagined.
• However, the network does not exist in the
generality imagined by Weiser.
• Many of the devices contain computers, but
the computers do not communicate in a
“ubiquitous” way.
Why?
• I think that mainly because what Weiser
suggested is not practical nor possible.
• The second requirement (the network part)
is much more complex than initially
thought.
Technical Problems
• It is not clear whether this network will be based
on the current Internet infrastructure (IP based), or
it will require a new, completely different
approaches.
• Even much smaller ad-hoc networks could not use
IP as the based protocol  new protocols like
Blue Tooth, etc.
• New schemes of routing: content based, smart
messages, etc.
Other Problems
• Security would become a nightmare. The
idea that cryptographic techniques will
solve this problem is a joke.
• Flexibility.
Conclusions
• A good starting paper, that tries to present what
ubiquitous computing is and how it can be used.
• However, the paper suggests more that this idea is
not practical and extremely difficult to implement
in a robust manner.
• Low power computers exist and will be used in a
lot of devices, but not in a global network.
• Some much narrow projects might benefit from
low power computers communicating between
each other, like sensor networks.