SAP BASIS.

SAP Basis is the foundation of SAP software functioning like an operating system in the SAP environment. The ABAP language environment, including the syntax checking, code generation and runtime system, is part of the SAP Basis component. SAP Basis is the technological platform that supports the entire range of SAP applications, now typically implemented in the framework of the SAP Web Application Server. In that sense SAP Basis can be seen as the 'operating system' on which SAP applications run. Like any operating system, SAP Basis contains both low-level services (for example memory management, database communication or servicing Web requests) and high-level tools for end users and administrators. These tools can be executables ("SAP kernel") running directly on the underlying operating system, transactions developed in ABAP, or Web-based interfaces.
SAP Basis also provides a layer of abstraction between the business applications and the operating system and database. This ensures that applications do not depend directly upon a specific server or database platform and can easily be ported from one platform to another.So the SAP AG had offer ERP in Multi OS platforms and Databases.Currently Support OS like Windows, RHEL, SUSE, HP-UX, AIX, Oracle-SunSolaris etc and DB: Oracle, DB2-LUW, MaxDB, MS-SQL Server and plant to include Sybase in his portfolio.

Source: http://en.wikipedia.org/wiki/ABAP

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