From: Mobile and disconnected computing

Two significant aspects of mobile computing give applications in this
environment a very different flavour.

- The dynamic nature of the environment forces applications to handle
  changes in the availability and allocation of software resources.
  Dynamic changes to environment variables [Schilit, 93], change in
  the available version of a library [Goldstein, 94] and the ability
  to lookup and retrieve objects from remote locations [Theimer, 93]
  are all required to solve this problem.  For the very same reasons,
  user interfaces add on an extra dimension, an issue which very few
  have addressed so far [Landay & Kaufmann, 93]. All this has caused
  certain vendors to move towards interpreted environments, based on
  scripting(??) languages as such as Script-X (Kaleida) and Open
  Scripting Architecture (Apple).

- Money will be a constituent of many of the transactions and
  applications that mobile computers will typically be used for.
  Hence, many pieces of system software will be required to handle,
  understand and optimise the use of money [Kulkarni, 94].  As
  mentioned by Ed Frank at the ICDCS '93 panel discussion on mobile
  computing, transaction involving `money and sex' may well become the
  biggest uses of the mobile computer.  Some initial forays into
  reviewing policies for pricing Internet services [Shenker, 93] may
  prove to be very useful and so will the experience of current
  consumer service providers such as CompuServe and America Online.
  This area will perhaps show the biggest divergence in the years to
  come, since applications will be far more customer-needs driven than
  technology-driven, as they have been in the past.

Finally, aspects of hardware support are critical to positioning any
discussion on mobile computing.  The most ambitious system is perhaps
the ParcTab system [Schilit, 93] under development at Xerox PARC.  The
ParcTab is a PDA that communicates via infrared data packets to a
network of infrared transceivers.  The network, designed for use
within a building, designates each room as a communication cell.  This
infrastructure has the responsibility for providing reliable service
as the ParcTab user moves from room to room.  More general purpose but
less ambitious PDAs are currently available from AT&T (EO), Apple
(Newton), IBM (Simon) etc.  Almost all recognise some alternate form
of input, such as handwriting.  The capabilities of these PDAs are
sure to increase in the coming years, and hopefully their prices will
not follow a similar trend.