Advantages of Distributed Systems over Centralized Systems:
Economics:
Microprocessors
offer a better price/performance than mainframes
Speed:
A
distributed system may have more total computing power than a mainframe
Inherent
distribution:
Some
applications involve spatially separated machines
Reliability:
If
one machine crashes, the system as a whole can still survive
Incremental
growth:
Computing
power can be added in small increments
Advantages of Distributed Systems over Isolated Computers:
Data
sharing:
Allow
many users access to a common data base
Device
sharing
Allow
many users to share expensive peripherals like color printers
Communication
Make
human to human communication easier, for example, by electronic mail
Flexibility
Spread
the workload over the available machines in the most cost effective way
Disadvantages of Distributed Systems:
Software:
Little
software exists at present for distributed systems
Networking
The
network can saturate or cause other problems
Security
Easy
access also applies to secret data
- With the current state of the art, we do not have much experience in designing, implementing and using distribute software.
What kinds of operating systems,
programming languages, and applications are appropriate for these systems?
How much should the users know about the
distribution?
How much should the system do and how
much should the users do?
Applying more research, this problem
would diminish, but in the present situation, it is still a concern.
- It can lose messages, which requires special software to be able to recover, and it can become overloaded. When the network saturates, it must either be replaced or a second one must be added. In both cases, some portion of one or more buildings may have to be rewired at great expense, or network interface boards may have to be replaced (e.g, by fiber optics). Once the system comes to depend on the network, its loss or saturation can negate most of the advantages the distributed system was built to achieve.
- If people can conveniently access data all over the system, they may equally be able to conveniently access data that they have no business looking at. In other words, security is often a problem. For data that must be kept secret at all costs, it is often preferable to have a dedicated, isolated personal computer that has no network connections to any other machines, and is kept in a locked room with a secure in which all the floppy disks are stored.
