Thick clients, also called heavy clients, are full-featured computers that are connected to a network. Unlike thin clients, which lack hard drives and other features, thick clients are functional whether they are connected to a network or not.
While a thick client is fully functional without a network
connection, it is only a "client" when it is connected to a server. The
server may provide the thick client with programs and files that are
not stored on the local machine's hard drive. It is not uncommon for
workplaces to provide thick clients to their employees. This enables
them to access files on a local server or use the computers offline. When a thick client is disconnected from the network, it is often referred to as a workstation.
A fat client still requires at least periodic connection to a network
or central server, but is often characterized by the ability to perform
many functions without that connection. In contrast, a thin client
generally does as little processing as possible and relies on accessing
the server each time input data needs to be processed or validated.
Introduction
In designing a client–server application, a decision is to be made as
to which parts of the task should be executed on the client, and which
on the server. This decision can crucially affect the cost of clients
and servers, the robustness and security of the application as a whole,
and the flexibility of the design to later modification or porting.
The characteristics of the user interface often force the decision on
a designer. For instance, a drawing package could choose to download an
initial image from a server and allow all edits to be made locally,
returning the revised drawing to the server upon completion. This would
require a thick client and might be characterized by a long time to
start and stop (while a whole complex drawing was transferred) but quick
to edit.
Conversely, a thin client could download just the visible parts of
the drawing at the beginning and send each change back to the server to
update the drawing. This might be characterized by a short start-up
time, but a tediously slow editing process
History
The original server clients were simple text display terminals including Wyse VDUs,
and thick clients were generally not used until the increase in PC
usage. The original driving force for thin client computing was often
cost; at a time when CRT terminals and PCs were relatively expensive,
the thin-client–server architecture enabled the ability to deploy the
desktop computing experience to many users.
As PC prices decreased,
combined with a drop in software licensing costs, thick client–server
architectures became more attractive. For users, the thick client device
provided a more-responsive platform and often an improved Graphical User Interface (GUI)
than could be achieved in a thin client environment. In more recent
years, the Internet has tended to drive the thin client model despite
the prodigious processing power that a modern PC has available.
Centrally hosted thick client applications
Probably the thinnest clients (sometimes called "Ultra Thin") are remote desktop applications, for example the X Window System, Citrix products and Microsoft's Terminal Services,
which effectively allow applications to run on a centrally-hosted
virtual PC and copy keystrokes and screen images between the local PC
and the virtual PC. Ironically, these ultra-thin clients are often used
to make available complex or data-hungry applications which have been
implemented as thick clients but where the true client is hosted very
near to the network server
Advantages of thick clients
- Lower server requirements. A thick client server does not
require as high a level of performance as a thin client server (since
the thick clients themselves do much of the application processing).
This results in drastically cheaper servers.
- Working offline. Thick clients have advantages in that a constant connection to the central server is often not required.
- Better multimedia performance. Thick clients have advantages
in multimedia-rich applications that would be bandwidth intensive if
fully served. For example, thick clients are well suited for video gaming.
- More flexibility. On some operating systems software products
are designed for personal computers that have their own local
resources. Running this software in a thin client environment can be
difficult.
- Using existing infrastructure. As many people now have very fast local PCs, they already have the infrastructure to run thick clients at no extra cost.
- Higher server capacity. The more work that is carried out by
the client, the less the server needs to do, increasing the number of
users each server can support.
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