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Evolution of Client-Server Computing

The evolution of Client-Server Computin has been driven by business needs, as

well as the increasing costs for host (mainframe and midrange) machines and

maintenance, the decreasing costs and increasing power of micro-computers

and the increased reliability of LANs( Local Area Networks).In the past twenty years, there are dramatic improvements in the hardware and

software technologies for micro-computers. Micro-computers become

affordable for small businesses and organisations. And at the same time their

performances are becoming more and more reliable. On the other hand, the

drop in price for mainframe is growing at a slower rate than the drop in its

price. Little developments have achieved with mainframes.

The following are the improvements made by micro-computers:

Hardware: The speed of desktop microprocessors has grown exponenetially,from a 8MHz 386-based computers to 100Hz-based pentium-based

microprocessors. These mass-produced microprocessors are cheaper and more

powerful than those used in mainframe and midrange computers. On the other

hand, the capacity of main memory in micro-omputers has been quafrupling

every three years. Typically main memory size is 16 Megabytes nowadays.

Besides, the amount of backup storage and memory such as hard disks and CD-

ROMs that are able to support micro-computers has also puts an almost

unlimited amount of data in reach for end-users.

Software: The development and acceptance of GUIs ( Graphical User

Interfaces) such as Windows 3.1 and OS/2 has made the PC working

environment more user-friendly. And the user are more efficient in learning

new application softwares in a graphical environment. Besides GUIs, the use of

multithreaded processing and relational databases has also contributed to the

popularity of Client-Server Computing.

Evolution

Client/server computing was created because of a need for computer managers to be

able to respond quickly to business demands, which they could not do easily with the

central, mainframe-based applications. Application development time was too slow,

and the results could not be tailored for the special needs of each department. The

personal computer environment allowed the users to have computing power and data

under their control. Unfortunately, this environment did not lend itself to collaboration

between workers. There was a great need to create a system that would work for each

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departmental to have control over their own formatting and data usage standards. This

led to departmental level client/server. (Stallings & Van Slyke, 1997)

The next step was a move to a two-tier, client/server system. The only real change

here was that a true DBMS was substituted for the File Server. This database server is

a computer that is responsible for database storage, access, and processing in aclient/server environment. The client workstation here is responsible for managing the

user interface, including presentation logic, data processing logic and business rules

logic. The database server is responsible for database storage, access, and processing.

This allowed for a multi-user system that was very reliable which made it a good

solution for many different problems. The problems with two-tier unfortunately soon

became obvious. A two-tier system does not scale well and is not suitable for

enterprise computing. Management problems grow with the size of the system.

This led to the development of a three-tier system. Adding an application server, to

handle business and data logic, created the three-tier system. This improvementprovided more power, reduced the need for software on the client and added more

power and scalability at reduced support costs. Three-tier architecture has the database

as the top tier. It works like any client-server environment on a server, waiting to

process data requests from approved users.

The middle tier acts as a mediator, processing requests coming from the user and from

the database. It maintains a full-time connection to the database using either native

drivers, open database connectivity (ODBC) or Java database connectivity (JDBC).

The middle tier often has its own user login to make that connection. The database

interaction all occurs at the middle tier. Significantly, the database thinks that there is

only one user presently accessing it in this model. Therefore, with a client-server

database like Oracle or Sybase or SQL Server facilitating 500 people, the system can

only detect the one user.

At the bottom of the structure is a very thin "client" tier probably written in Java or a

type of Web-based technology that allows it to be used within your browser. The

connection from the client tier to the middle tier is carried out through technologies

designed specifically to accommodate requests depending on the hardware platform

and the development environment.

This type of technology has several advantages. First, the part of the software which

must be transmitted to the user's terminal, can be quite small. Having a very thin client

lets a limited amount of data load, this allows faster start-up times. In large businesses

this kind of architecture provides a simple means of centralized configuration

management. As this layer needs only to handle the results of the application, the thin

client can easily handle a multi-platform environment. These improvements also came

with some challenges. Within this type of system there are more potential points of

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failure with few tools are available, performance sometimes suffers and upgrades

become a significant task.

The Internet is an example of a successful adaptation of a three-tier client/server

system that uses an open set of standards, which allows various networks to

interconnect. The introduction of a separate Web server expands the power and use ofthe system. A mainframe can be brought into the system allowing the use of existing,

legacy applications in a new context. Microsoft, IBM, and Netscape are coming

together to promote their own version of what should be. (Anonymous, 1996;

Vandersluis, 1999)