2 system privileges :SYSDBA & SYSOPER

SYSDBA and SYSOPER
Administrative privileges that are required for an administrator to perform basic database operations are granted through two special system privileges, SYSDBA and SYSOPER. You must have one of these privileges granted to you, depending upon the level of authorization you require.
The following are the operations that are authorized by the SYSDBA and SYSOPER system privileges:
System Privilege Operations Authorized SYSDBA Perform

1. STARTUP and SHUTDOWN operations
2. ALTER DATABASE: open, mount, back up, or change character set
3. CREATE DATABASE
4. CREATE SPFILE
5. ARCHIVELOG and RECOVERY
6. Includes the RESTRICTED SESSION privilege

Effectively, this system privilege allows a user to connect as user SYS.

SYSOPER Perform

1. STARTUP and SHUTDOWN operations
2. CREATE SPFILE
3. ALTER DATABASE OPEN/MOUNT/BACKUP
4. ARCHIVELOG and RECOVERY
5. Includes the RESTRICTED SESSION privilege

This privilege allows a user to perform basic operational tasks, but without the ability to look at user data.
The manor in which you are authorized to use these privileges depends upon the method of authentication that you choose to use.
When you connect with SYSDBA or SYSOPER privileges, you connect with a default schema, not with the schema that is generally associated with your username. For SYSDBA this schema is SYS; for SYSOPER the schema is PUBLIC.