Because of their speed and accuracy, computers have traditionally been utilized for commercial application development. Commercial applications typically have many, distinct levels, resulting in a multi-tier distributed computing approach. This concept is entirely based on the client/server computer paradigm.
Client: A client is a computer that end-users use to run applications that is linked to a network in order to use the services provided by servers such as a database server, file server, or web server. As a result, a client will only run user programs and communicate with servers for data and file services. End users enter data and interact with the business application, which is run by clients.
Server: A server is a computer system that is connected to the internet and delivers services to other computers on the network. File servers, application servers, database servers, e-mail gateways, and communication servers are all examples of servers. These computers run Novell NetWare, Windows NT, or UNIX OS, which are network operating systems.
Client-Server Architecture aka Two-Tier Architecture:
The client/server computing model is one in which data is captured and validated on a computer known as a client, and validated data (captured by the client) is saved on another computer known as a server.
An application’s architecture is split into two parts: a front-end client component and a back-end server component. On a workstation, the client component collects data from the user, prepares it for the server, and sends a request to the server. The server is waiting for requests from its clients on the back end. When the server receives a request, it processes it and sends the desired data to the client. The data is subsequently presented to the user using the client’s own user interface.
Without the use of an intermediate, the client communicates directly with the server. This model’s weakness is that it is difficult to scale. If the server becomes overburdened by client traffic, the typical approach is to replace the server hardware with a faster processor and additional memory. There is, however, a limit to how fast the CPU can go. The data is saved on the server, and business or transaction rules are applied to each client machine. Every client machine faces the difficulty of software up-gradation whenever business or transaction regulations change.
Please also read-
Multi-Tier Architecture.
Big Data and SQL 
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