What is Centralized System ?

Centralized systems run on a single computer system and do not interact with other computer systems.

It is a single user database system which can be used on personal computer and also on the mainframe system.

A centralized computer system shown in above Fig. consists of one to a few CPUS and a number of device controllers, that are connected through a common bus that provides access to stored memory. The CPU and device controllers can execute concurrently competing for memory access. The CPU have local cache memory that stores local copies of parts of memory to speed up access to data and to reduce the number of times that the CPU needs to access the shared memory.

A single user system is a desktop unit used by a single person. It has only one CPU and one or two hard-disks. It has an operating system that may support only one user.

Database system designed for a single user system does not provide many of the facilities that a multiuser database system provides. Such types of systems are intended for a specific work goal and are capable of operating on their own without any need of communication with other nodes.

Advantages:

• Increased Throughput : Number of queries executed per unit of time can be increased with more than one processor.
• High Execution Speed: Query intercommunication delay involved.

Disadvantages:

• No Support for Failure Recovery : As there is only one node, if it fails/crashes whole system will crash and there is no means or very few chances of recovery after failure. Thus, operating node itself becomes a major bottleneck.
• No support for concurrency control and SQL : Many such systems do not support concurrency control and querying using SQL. Rather such systems provide simpler query languages, such as a variant of Query by Example (QBE).