Distributed Systems: Concepts and Design. by George Coulouris. Exercise Solutions

Edition 3
By George Coulouris, Jean Dollimore and Tim Kindberg
Addison-Wesley, ©Pearson Education 2001
Chapter 1 Exercise Solutions


1.1 Give five types of hardware resource and five types of data or software resource that can usefully
be shared. Give examples of their sharing as it occurs in distributed systems.
1.1 Answer



Hardware:
CPU: compute server (executes processor-intensive applications for clients), remote object server
(executes methods on behalf of clients), worm program (shares cpu capacity of desktop machine with the
local user). Most other servers, such as file servers, do some computation for their clients, hence their cpu
is a shared resource.
memory: cache server (holds recently-accessed web pages in its RAM, for faster access by other local
computers)
disk: file server, virtual disk server (see Chapter 8), video on demand server (see Chapter 15).
screen: Network window systems, such as X-11, allow processes in remote computers to update the
content of windows.
printer: networked printers accept print jobs from many computers. managing them with a queuing
system.
network capacity: packet transmission enables many simultaneous communication channels (streams of
data) to be transmitted on the same circuits.
Data/software:
web page: web servers enable multiple clients to share read-only page content (usually stored in a file, but
sometimes generated on-the-fly).
file: file servers enable multiple clients to share read-write files. Conflicting updates may result in
inconsistent results. Most useful for files that change infrequently, such as software binaries.
object: possibilities for software objects are limitless. E.g. shared whiteboard, shared diary, room booking
system, etc.
database: databases are intended to record the definitive state of some related sets of data. They have been
shared ever since multi-user computers appeared. They include techniques to manage concurrent updates.
newsgroup content: The netnews system makes read-only copies of the recently-posted news items
available to clients throughout the Internet. A copy of newsgroup content is maintained at each netnews
server that is an approximate replica of those at other servers. Each server makes its data available to
multiple clients.
video/audio stream: Servers can store entire videos on disk and deliver them at playback speed to multiple
clients simultaneously.
exclusive lock: a system-level object provided by a lock server, enabling several clients to coordinate their
use of a resource (such as printer that does not include a queuing scheme).

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