DIFFERENCE BETWEEN SYS and SYTEM

The following administrative user accounts are automatically created when you install Oracle Database. They are both created with the password that you supplied upon installation, and they are both automatically granted the DBA role.

• SYS
  This account can perform all administrative functions. All base (underlying) tables and views for the database data dictionary are stored in the SYS schema. These base tables and views are critical for the operation of Oracle Database. To maintain the integrity of the data dictionary, tables in the SYS schema are manipulated only by the database. They should never be modified by any user or database administrator. You must not create any tables in the SYS schema.
  The SYS user is granted the SYSDBA privilege, which enables a user to perform high-level administrative tasks such as backup and recovery.
• SYSTEM
  This account can perform all administrative functions except the following:
• Backup and recovery
• Database upgrade

SYS

• Automatically created when Oracle database is installed
• Automatically granted the DBA role
• Has a default password: CHANGE_ON_INSTALL (make sure you change it)
• Owns the base tables and views for the database data dictionary
• The default schema when you connect as SYSDBA

Tables in the SYS schema are manipulated only by the database. They should never be modified by any user or database administrator, and no one should create any tables in the schema of user SYS. Database users should not connect to the Oracle database using the SYS account.

SYSTEM

• Automatically created when Oracle database is installed
• Automatically granted the DBA role
• Has a default password: MANAGER (make sure you change it)
• Used to create additional tables and views that display administrative information
• Used to create internal tables and views used by various Oracle database options and tools

Never use the SYSTEM schema to store tables of interest to non-administrative users.