●●● ●●●● 2.1 Operating System Services :: ● ●●●● Accounting(登账) To keep track of which users use how much and what kinds of computer resources o Protection and security o Protection involves ensuring that all access to system resources is controlled o security requires user to authenticate himself to the system, extends to defending external l /O devices from invalid access attempts9 2.1 Operating System Services ⚫ Accounting （登账） ⚫ To keep track of which users use how much and what kinds of computer resources ⚫ Protection and security ⚫ Protection involves ensuring that all access to system resources is controlled ⚫ Security requires user to authenticate himself to the system, extends to defending external I/O devices from invalid access attempts