operating system

operating system

1. CPU

   • modern processors can execute 4 billion instructions every second.
   • while a processor waits for other components to catch up, it is not doing anything
   • an OS will make use of this dead time by allocating CPU time to do different processes
   • multi-tasking
     • multi- tasking is where a processor is doing two tasks simultaneously. in reality the processor runs the commands separately, filling the time when waiting for other components

2. why have an OS?

   • each PC has a combination of CPU, hard disk, etc. writing software to talk directly to every different piece of hardware would be impossible.
   • If we programmed directly for the hardware, we would have to implement all of these things manually. An operating systems deal with all the things mentioned above, leaving the program to only focus on its own function.
   • if we write a program in C++, it can compile for windows, Linux, mac or android. this means you don't have to worry about what hardware the user has.

3. interrupts

   • an interrupt is a method to immediately pause execution of all processes and execute a new one
   • the OS will manage the interrupt requests, and backing up the existing processes so they can be resumes when the interrupt is finished
     • backing store
       • manages backups of important data
         • local
         • cloud
   • interrupts can be triggered by hardware or software

4. RAM

   • each program needs RAM, the allocation or RAM must be managed
   • in order to ensure there is enough memory for each program that is running, RAM is split into "pages"
   • this prevents the other programs from getting data from other programs

5. peripherals

   • a peripheral is a device that connects to a computer, such as a printer or game controller
   • a PC can connect two different game console controllers. the operating system handles the different controllers
   • drivers
     • operating systems is device drivers use to communicate to different peripherals
     • a device driver maps out the operating system's commands to the devices commands

6. security

   • operating systems have a range of security features
   • an OS will do things like verify a username and password, and ensure that the program doesn't damage system files
   • interface
     • an interface is the mechanism by which the user controls the function of the computer
     • most operating system support two types of interface- a GUI (graphical user interface) and a CLI (command line interface)
     • a GUI is used by most PC and phone operating systems. there is a graphical representations of the computer functions are shown to the user and controlled by touchscreen, mouse and keyboard.
     • a CLI is a text-based interface. this is where the user types commands, and results are shown as text. nearly every operating system provides CLI. CLI is harder to use but is lightweight and robust, they use fewer system resources and are unlikely to break or crash.