A centralised database (sometimes abbreviated CDB) is a database that is located, stored, and maintained in a single location. This location is most often a central computer or database system, for example a desktop or server CPU, or a mainframe computer.  In most cases, a centralised database would be used by an organisation (e.g. a business company) or an institution (e.g. a university.) Users access a centralised database through a computer network which is able to give them access to the central CPU, which in turn maintains to the database itself.
All of the information stored on the CBS is accessible from a large number of different points, which in turn creates a significant amount of both advantages and disadvantages.
The first ever created computers were overly expensive and did not have separate terminals. Thus, the need for centralised computing quickly arose. As a result, a way for data to be not just be processed, but to also be organised and stored was discovered. This gave way to the earliest versions of databases, their respective database management systems (DBMS) and, in turn, centralised databases.
With the growing popularity of computers, more and more types of database orientation and design were introduced. Centralised databases however are still used today, especially where storing and processing data in large enterprises is concerned.
Centralised databases hold a substantial amount of advantages against other types of databases. Some of them are listed below:
- Data integrity is maximised and data redundancy is minimised, as the single storing place of all the data also implies that a given set of data only has one primary record. This aids in the maintaining of data as accurate and as consistent as possible and enhances data reliability.
- Generally bigger data security, as the single data storage location implies only a one possible place from which the database can be attacked and sets of data can be stolen or tampered with.
- Better data preservation than other types of databases due to often-included fault-tolerant setup.
- Easier for use by the end-user due to the simplicity of having a single database design.
- Generally easier data portability and database administration.
- More cost effective than other types of database systems as labour, power supply and maintenance costs are all minimised.
- Data kept in the same location is easier to be changed, re-organised, mirrored, or analysed.
- All the information can be accessed at the same time from the same location.
- Updates to any given set of data are immediately received by every end-user.
Centralised databases also have a certain amount of limitations, such as those described below:
- Centralised databases are highly dependent on network connectivity. The slower the internet connection is, the longer the database access time needed will be.
- Bottlenecks can occur as a result of high traffic.
- Limited access by more than one person to the same set of data as there is only one copy of it and it is maintained in a single location. This can lead to major decreases in the general efficiency of the system.
- If there is no fault-tolerant setup and hardware failure occurs, all the data within the database will be lost.
- Since there minimal to none data redundancy, if a set of data is unexpectedly lost it is very hard to retrieve it back, and in most cases it would have to be done manually.
Centralised databases vs. Distributed databases
The underlying idea of centralised databases is that they should be able to receive, maintain, and complete every single request that the main system must perform by themselves. There is only one database file, kept at a single location on a given network.
A distributed database, however, is a database in which all the information is stored on multiple physical locations. Distributed databases are divided into two groups: homogeneous and heterogeneous. It relies on replication and duplication within its multiple sub-databases in order to maintain its records up to date. It is composed of multiple database files, all controlled by a central DBMS.
The main differences between centralised and distributed databases arise due to their respective basic characteristics. Differences include but are not limited to:
- Centralised databases store data on a single CPU bound to a single certain physical/geographical location. Distributed databases, however, rely on a central DBMS which manages all its different storage devices remotely, as it is not necessary for them to be kept in the same physical and/or geographical location.
- As outlined above, centralised databases are easier to maintain up to date than distributed databases. This is so because distributed databases require additional (often manual) work to keep the data stored relevant, and to avoid data redundancy, as well as to improve the overall performance.
- If data is lost in a centralised system, retrieving it would be much harder. If, however, data is lost in a distributed system, retrieving it would be very easy, because there is always a copy of the data in a different location of the database.
- Designing a centralised database is generally much less complex than designing a distributed database, as distributed database systems are based on a hierarchical structure.
- Lake, Peter (2013). Concise Guide to Databases: A Practical Introduction. New York City: Springer. p. 37. ISBN 978-1447156000.