Chapter 6 - OS

operating system (OS)

System software that provides an INTERFACE between the user or application program AND the computer hardware. 4 MAIN TASKS: 1) Provide user Interface. 2) Offer System Security and Protection. 3) Manage Resources Efficiently. 4) Use Resources Safely AKA The most important software on a computer! OS manages: 1) the hardware 2) the software resources (user wants resources, the OS delivers) 3) the services computer programs want Found in lecture Chapter 6 Part 1 - Operating Systems

4 main tasks of OS

1) Provide User Interface 2) Offer System Security and Protection (OS acts like a security guard) 3) Manage Resources Efficiently 4) Use Resources Safely Found in lecture Chapter 6 Part 1 - Operating Systems

Why do we want an interface between the user and the hardware?

-to hide hardware details -to create a user-friendly environment -to prevent damage to system (hardware and data) Found in lecture Chapter 6 Part 1 - Operating Systems

What are some well-know operating systems?

Desktops/Laptops: Linux, MacOS, Windows Mobile: Apple iOS, Google Android Found in lecture Chapter 6 Part 1 - Operating Systems

GUI

Graphical User Interface User interfaces today are graphical (as users found text interface "cumbersome"). However, text based interface can be very efficient. Found in lecture Chapter 6 Part 1 - Operating Systems

superusers

user(s) who have more privileges (admin) than others privileged users, usually computer center employees, with the ability to access and maintain password files Found in lecture Chapter 6 Part 2 - Operating Systems

process

a program in execution Found in lecture Chapter 6 Part 2 - Operating Systems

fundamental OS task

process management Found in lecture Chapter 6 Part 2 - Operating Systems

running state

the process is executing instructions Found in lecture Chapter 6 Part 2 - Operating Systems

ready state

the process is runnable (ready to run), but not running process is waiting in ready queue Found in lecture Chapter 6 Part 2 - Operating Systems

blocked/waiting state

the process is waiting for some event to occur Found in lecture Chapter 6 Part 2 - Operating Systems

new state

the process is being created by the OS Found in lecture Chapter 6 Part 2 - Operating Systems

exit state

the OS is cleaning up a terminating process Found in lecture Chapter 6 Part 2 - Operating Systems

time slice

process moves from RUNNING to READY occurs when process has run for a MAX length of time exists for processes "hogging" the CPU process kicked off processor (process goes from RUNNING back to READY) if SMALL time slice -> HUGE overhead costs (to move process from ready to running back to ready; think of OS tables that need to be updated / registers that get changed) if LARGE time slice -> system response time is SLOW (turn around time for response gets too slow; users need to wait longer to get processor time) Found in lecture Chapter 6 Parts 2 and 3 - Operating Systems

ready queue

line of processes ready to run Found in lecture Chapter 6 Part 2 - Operating Systems

virtual memory

"virtualizes" memory/RAM locations (abstraction) think of VM as "simulated physical memory (RAM)" Found in lecture Chapter 6 Part 3 - Operating Systems

I/O intensive process

process is often BLOCKED Found in lecture Chapter 6 Part 3 - Operating Systems

compute intensive process

process is mainly RUNNING or READY Found in lecture Chapter 6 Part 3 - Operating Systems

deadlock

when two or more processes are permanently blocked on each other one way to resolve = Deadlock Prevention if process can't get everything it needs, it gets nothing other types of deadlocks (and solutions) exist Found in lecture Chapter 6 Part 3 - Operating Systems

processor utilization

percentage of time that the processor is busy Found in lecture Chapter 6 Part 3 - Operating Systems

What does the OS provide?

- Scheduler - Memory Managers (Loaders, Garbage collectors, Linkers) - Information Managers (File systems, Database systems) - Language Support (Interpreters, Compilers, Assemblers) - I/O manager (Keyboard, printer, network connection) - Utilities (Text editors, graphics routines). Found in lecture Chapter 6 Part 1 - Operating Systems

example OS commands

-Load Program -Run Program -Save info to file/directory -Retrieve previously stored file -List all files for user -Delete file -Rename file -Copy files from one I/O device to another -Print file on specified I/O device -Establish network connection -Let user set password -Let user change password -Relay memory usage -Relay data storage usage