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When you log on to an SAP System, you log on to a particular client of this system. Any activities you carry out in the system are always carried out in one client. When you plan your SAP system landscape, you must consider which clients you need for which activities.

By assigning activities to be performed in a client, you give each client a particular role. This section describes the most important client roles.

Since you need to adapt the SAP software for your own business needs, each SAP system landscape requires a client where Customizing settings, and possibly ABAP Workbench developments, can be made. This client is known as the Customizing and development client, or Customizing client for short. The abbreviation CUST is used for this client.

Before you can use the Customizing settings and Workbench developments productively, you need to test them extensively for errors. Any faulty settings can seriously disrupt productive operations, and at worst, lead to the loss of productive data. The integrated nature of the various SAP applications means that there are many dependencies between the different Customizing settings. Even an experienced Customizing developer may not discover these dependencies immediately. The correctness of the settings can only be guaranteed with extensive testing. The client where these tests are made is the Quality Assurance Client, QTST for short.

A separate client is required for productive use of the SAP System. So that this client can be used without disruption, it is essential that no Customizing settings or Workbench developments are made here, and also that no tests are carried out. This client is known as the Production Client, PROD for short.

These three clients, CUST, QTST and PROD, are the central clients that exist in every system landscape. Standard system landscapes have precisely one client for each of these client roles.

We recommend that you make all your Customizing settings in a single Customizing client, and then use the CTS to transport them to the other clients.

We also recommend that you do not make any Customizing settings or Workbench developments in the quality assurance or production clients. You can make sure of this by making appropriate client settings.

In addition to the central clients, you can also set up other clients for other tasks. However, you must remember that each extra client takes up additional system resources (main memory and database space). They also need to be administrated. For example, you need to set up and administrate access authorization for the users, and also distribute any changes to other clients with the CTS. You must weigh up the advantages and disadvantages of setting up other clients.

Examples of other client roles are:

Development test client (TEST)
Developers can use this client to test their Customizing settings and Workbench developments, before they release their change requests. In this client the developers can create test application data for realistic tests. If they discover errors, they can remove them in the Customizing client. A development test client is always set up in the same SAP System as the Customizing client. This means that any changes that are made to cross-client data in the Customizing client are also immediately visible in the development test client. Changes to client-specific data are copied from the Customizing client to the development test client using a special client copy function. The client copy function uses the unreleased change requests from the Customizing client to do this. The development test client is set so that you cannot make changes to Customizing data and Repository objects.
Prototype or sandbox client (SAND)
You can use this client to test any client-specific Customizing settings if you are not sure whether you want to use them in this form. Any settings that you want to keep are then entered in the Customizing client. To prevent conflicts between the prototype client settings and real settings in the Customizing client, you cannot make changes to cross-client Customizing data and Repository objects in the prototype client. The CTS does not record changes made to client-specific Customizing data, and does not transport them from the prototype client. You can make sure of this by making appropriate client settings.
Training client (TRNG)
To prepare end users for new functions that are to be transported into the production client, you can set up a training client. The users can use the new functions in this client with specially created application data. This client is set so that you cannot make changes to Customizing data and Repository objects.