What is a client in SAP

       Clients in R/3 system and default users with passwords:

 There are 3 standard clients in sap r/3  system. They are 000, 001 and 066. These three clients come with default  users along with default passwords. I have listed in the following  paragraphs.

What is a client: A client is an independent unit within the R/3 system or an area in the system with data on which a user works.
We have to do client copy right after  installation of the software as our first job to begin the technical  phase of implementation. We have to copy from one of the standard  clients available. We can use copied clients for testing, training or  for starting real customization.
We will discuss about what is data and  what types of data is available in the sap R/3 system before going into  the explaining of definition of the standard clients.

Data: The information  residing in the database tables is called data. There are different  types of data involved in the R/3 system. They are client dependent  data, client-independent data and the client repository data.

Client dependent data: The data which is accessible through a particular client is called  client dependent data. The user data is one of the examples of client  dependent data.

Client-independent data: The data which can be accessible from any client or which is common to  any client in the system is called client-independent data. The  transaction code or t-code data is example of the client-independent  data.

Client repository data: The different application programs which makes SAP runs is called  client repository data. The transaction data, application data,  customizing data are other different types of data of the sap r/3  system.

Standard clients of the SAP R/3 system:

000 Client: This client  is called as master client in the r/3 system. This client is included  in the sap r/3 system as default. We can find this client in the system  as soon as we install sap r/3 software. Client 000 contains a simple  organizational structure of a test company and includes parameters for  all applications, standard settings, configurations for the control of  standard transactions and examples to be used in many different profiles  of the business applications. For these reasons, 000 is a special  client for the R/3 system since it contains the client?independent  settings. We can access the entire standard data with this client. We  should not do any changes in the data through master client. The default  users of this client are mentioned below along with default passwords.
 - User name: sap* - Password: This password will be set by the person during the sap r/3 installation - User name: ddic - Password: This password will be set by the person during the sap r/3 installation

001 client: This client is best example  for customizing or development client and we can access entire  customizing data. This client is a copy of the 000 client including the  test company. This client?s settings are client-independent if it is  configured or customized. This client is reserved for the activities of  preparing a r/3 system for the production environment. The customers of  the SAP normally use this client as a source for copying other new  clients. The default users and passwords of this client are listed  below.
   
 - User name: sap* - Password: 06071992 - User name: ddic - Password: 19920706

066 Client: This client  also called as early watch client which is reserved for sap access. SAP  will access their customer systems using this client to perform the  Early Watch service. SAP will generate the performance report of its  customer system and this report is called as Early Watch report. The  default users of this client are listed below.
 - User name: sap* - Password: 06071992 - User name: earlywatch - Password: support