A criterion for classifying a database system is according to the number of users who can use the system concurrently. It can be divided into single-user and multi-user database systems.
1. Single User Database Systems :
In these DBMS, at one time, only a single user can access the database. Hence, the user can use all the resources at all times. All these systems are used for personal usage, such as personal computers experience. In this type of DBMS, both the physical and application layer can be used by the user.
2. Multi User Database Systems :
These DBMSs supports two or more than two users accessing the database simultaneously. Multi-user systems contains all the mini-computers and mainframe computers. In mainframe computer, the database may exist on a single computer and in other computers, the database may be distributed in multiple computers. Multiple users can update data while working together simultaneously.
Databases of Banks, insurance agencies, stock exchanges, supermarkets, etc.
Difference between Single User and Multi User Database Systems :
|Single User Database Systems||Multi User Database Systems|
|A DBMS is single-user if at most one user at a time can use the system.||A DBMS is multi-user if many/multi users can use the system and hence access the database concurrently.|
|Single-User DBMSs are mostly restricted to personal computer systems.||Most DBMSs are multi user, like databases of airline reservation systems, banking databases, etc.|
|Single user databases do not have multiprogramming thus, single CPU can only execute at most one process at a time.||Multiple users can access databases and use computer systems simultaneously because of the concept of Multiprogramming.|
|Example: Personal Computers.||Example: Databases of Banks, insurance agencies, stock exchanges, supermarkets, etc.|
A single central processing unit (CPU) can only execute at most one process at a time. However, multi-programming operating systems execute some commands from one process, then suspend that process and execute some commands from the next process, and so on. A process is resumed at the point where it was suspended whenever it gets its turn to use the CPU again.
Hence, concurrent execution of processes is actually interleaved, as illustrated in figure below –
The above figure shows two processes, A and B, executing concurrently in an interleaved fashion.
Interleaving keeps the CPU busy when a process requires an input or output (I/O) operation, such as reading a block from disk. The CPU is switched to execute another process rather than remaining idle during I/O time
Interleaving also prevents a long process from delaying other processes. If the computer system has multiple hardware processors (CPUs), parallel processing of multiple processes is possible, as illustrated by processes C and D in the above figure.
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