SAP BASIS forms the layer where the R/3 system functionality lies. Each R/3 has its own BASIS component. All SAP clients and modules use the BASIS layer through the R/3 system. What exactly does BASIS do in an SAP R/3 environment? The SAP R/3 BASIS module takes care of structures and control, processing, programming, data and storage in the SAP R/3. I am listing some of the important SAP BASIS alongwith their functions in short.

SAP BASIS T-Codes with explanations

SPRO - Display Implementation Guide IMG
SM35 - Display Batch Jobs
SE38 - ABAP/4 Editor (viewing ABAP codes and program documentation)
SE16 - Data browser (viewing and download tables)
SM31 - Table maintenance (viewing and download tables)
SU01 - Display users
SU02 - Display profiles
SU03 - Display authorizations
SECR - Repository Information System
SU24 - Authorization objects check under transactions
SUIM - Authorization Report Tree
Functional X-actions - Display access to all FI and SD functional transactions

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