In MS SQL database server some user have total access of the server so they can do what ever they want while some usiers can only able to manage security. To Limit the amount of administrative access for a user Server Roles are defined. All the server roles are described as under with highest administrative access granted:
Sysadmin have the authority to perform any task in SQL server. This role is only for the Database Administrators [DBA].
Serveradmin can set server wide configuration options. Like..how m,uch memory SQL server can use, how much information to send over the network in a single frame etc..,
Setupadmin can install replication and manage extended stored procedures.
Securityadmin user can manage security issues such as creating and deleting logins, reading the audit logs, granting users permissions to create database.
SQL server can run more than one task at a time by executing multiple processes. Processadmin can ebd/kill a process whenever any suspecious or hanged process are running on the server.
DBCreator can create database for a user and maintain it.
Diskadmin can manage and maintain files on the disk.