A one-system landscape consists of a production system (<PRD>). The following graphic outlines this one-system landscape and its clients as recommended according to the SAP guidelines.

If you own a Ready-to-Run system, your system is already preinstalled according to these guidelines.

The main advantage of a one-system landscape over a two- or multiple-system landscape are the lower hardware costs.

There are, however, the following disadvantages:

• You carry out all Customizing and development tasks in the production system. These changes can affect the current settings of your system directly.

• It is more difficult to introduce applications step-by-step in a one-system landscape.

For these reasons, if you have a one-system landscape, SAP strongly recommends that you make use of some of its additional services, for example the remote upgrade service.

The following graphic displays a one-system landscape in relation to the time-scale and the availability of the individual clients during each phase of its implementation:

In the production system <PRD>, clients CUST (200), SAND (210) and QTST (300), TRNG (310), PROD (400) and PPRD (410) are already available when the system is delivered.

The training client TRNG (310) and the practice client SAND (210) are re-initialized regularly by client copy. The production client PROD (400) is set up in the production system <PRD> after a successful integration test in the preproduction client PPRD (410).

A two-system landscape consists of a development system <DEV> and a production system <PRD>. The following graphic displays the two-system landscape and its clients as recommended in the ASAP guidelines.

If you own a Ready-to-Run system, your system is already preinstalled according to these guidelines.

The following graphic displays the availability of the individual clients in both <DEV> and <PRD> systems with regards to the individual implementation phases:

In the Customizing and development system <DEV>, clients CUST (200), SAND (210), QTST (300) and TRNG are already available when the system is delivered.

In the production system <PRD> the clients PROD (400) and PPRD exist (410).

The training client TRNG (310) and the practice client SAND (210) of the development system <PRD> are re-initialized regularly by client copy.

The production client PROD (400) in the production system <PRD> is set up after a successful integration test in the preproduction client PPRD (410).

A three-system, landscape consists of a development system <DEV>, a quality assurance system <QAS> and a production system <PRD>. The following graphic displays the three-system landscape and its clients as recommended in the ASAP guidelines.

A three-system landscape has additional advantages compared to a two-system landscape:

• You can divide the implementation of SAP applications into smaller, units that are easier to work with.

• You perform Customizing and development tasks in the development system and test them in the quality assurance system first on the project level.

• After performing the tests in the quality assurance system, you can transport specific objects later if an error occurs and the repeat the test.
• A three-system landscape simplifies a multi-step implementation of modules since these can be tested and released independently of each other.
• You can verify if the transports are complete in the quality assurance system without this having an effect in the production system.
• Functional tests (in the quality assurance system) and the integration test (in the production system) are separated from each other.

The following graphic displays the availability of the individual clients in the SAP system landscape in the <DEV>, <QAS> and <PRD> systems with regards to the individual implementation phases:

In the Customizing and development system <DEV> the CUST (200) and SAND (210) clients, and in the quality assurance system the QTST (300) and TRNG (310) clients are already available when the system is delivered. In the production system <PRD> the PROD (400) and PPRD (410) clients are available.

The training client TRNG (310) and the sandbox client SAND (210) for the development system <DEV> are re-initialized regularly by client copy. The production client PROD (400) in the production system <PRD> is set up after a successful integration test in the preproduction client PPRD (410).