System Architecture & Hardware Configurations Dr. D. Bilal IS 582 Spring 2009

System Architecture Two major system architectures: Hierarchical Client/Server

Hierarchical Architecture Processing and activities are controlled by the host system Remote computers connected to host system have limited functions (input/output)

Hierarchical Architecture Remote computers connected to the host system emulate “dumb” terminals in communicating with the host system. “Dumb” terminals have no or limited processing capabilities.

Client/Server Architecture Client: a user’s computer Server: a dedicated computer in a network shared by multiple users More than one server can exist in this architecture (e.g., database server, Web server, application server, e-mail server)

Client/Server Architecture A computing architecture in a LAN or WAN environment Clients on network perform certain processing functions when requesting information from a server in the network

Client/Server Architecture TCP/IP to establish communications between clients and servers Clients handle the user interface screen formatting, display of results, input/output make requests and send them to the application server

Client/Server Architecture Server searches for requested information and sends results to the client(s) Server performs database management, information retrieval, transaction and processing tasks. Server delivers access to files, applications, and network communications.

File Server Architecture User requests information from a server Entire database file is downloaded in the computer making the request results in slow communication between the user’s computer and the server.

File Server Architecture Software programs are loaded onto the server only Updates are performed in server Updates take less time to install than those in client/server architecture

Client/Server Architecture One client may connect to one or more servers: OPAC server, T-mail server, and other servers One server may connect to multiple clients concurrently.

Client/Server Architecture Each client that is connected in a client/server network must have part of the automation software (e.g., user interface) loaded into client hard disk to perform certain application tasks.

Client/Server Architecture If all OPACs in a network must have access to the Web, all clients must have a Web browser. If all clients must provide access to e-mail, they must have the e-mail client software loaded on them.

Client/Server Architecture Servers may be large scale computers, mid-range computers, or high speed microcomputers. True client/server means that the application was originally designed to run on a network (LAN or WAN).

Client’s Functions/Tasks Handles the user interface. Translates the user's request into the desired protocol. Sends the request to the server. Waits for the server's response. Presents the results to the user.

Server’s Functions/Tasks Receives a request/query from the client. Processes the query. Returns the results back to the client. Client presents the results to the user.

Two-Tier Server: Processes database tasks such as search and retrieval. Client: Processes application tasks. A request is generated in the client and transmitted to the server. The Database Management System that resides on the server searches for the desired information and transmits the results of the request to the client. The client present the information to the user on the screen.

Three-Tier Used when applications are in high demand. An additional server is used for application processing tasks. Both the client and the additional server perform application processing tasks. The other server performs the database management tasks (searching, retrieval, etc.).

Types of Client/Server: Thin Clients Computer terminals rather than desktop computers. Do little or no data processing tasks. Process information (input/output). Used to lower PCs and Macs cost used in a network.

Types of Client/Server: Thin Clients May be used as e-mail stations, Web access stations, and/or OPACs stations. Can co-exist with thick or fat clients in a network.

Options for Hardware Configurations Non-networked (a.k.a. stand-alone) Advantages Disadvantages Difference between stand-alone hardware configuration and stand-alone software configuration.

Options for Hardware Configurations Networked: LAN-based Advantages Disadvantages Networked: WAN-based