Open distributed Systems differ from Distributed Operating
systems in a fundamental way:
The support for distributed <#177#> applications<#177#> is provided by each
host in an open way. There is <#178#> middleware<#178#> between the
simple communciations facilities that each host provides and the
application. This layer ensures a high degree of
independence between the underlying system and applications.
In this way, the Distributed System Programmer may provide a
<#179#> different<#179#> Virtual Machine depending on the requirements of the
Application in question.
Each Host's Operating System must be supplemented with the toolset
adequate for the set of distributed applications that are
required for that host to participate. The full set is not
required - the application programmer picks and chooses appropriate
tools.
This has major advantages over monolithic Distributed Operating
Systems in terms of performance, management and scalability.
Distributed OS provide a common interface to the application
regardless of the physical platform, thus supporting homogeneity for
the application programmer.
#figure180#
Figure: Distributed Operating System