Operating Systems Flashcards
An operating system consists of layers. What are they and give a brief explanation?
1.1) Command Layer (shell/GUI) - Interface for the operating system. Accepts commands and requests.
1.2) User Applications
2) Service Layer - contains a set of functions called by programs and command layer for loading, managing and executing programs.
3.1) Kernel - Directly interacts and manages system and hardware resources allocating them to users and applications as needed.
3.2) Device Drivers - special programs that allow OS to communicate with hardware devices.
Describe what bootstrapping is
Bootstrapping is the process of loading the operating system into main memory from the hard disk and then transferring control to the starting location of the OS.
What are the three steps of bootstrapping?
1) At start, PC points to fixed address in BIOS where bootstrap loader is stored.
2) Bootstrap loader directs computer copy data from given memory locations into RAM
3) PC points to address in RAM where OS has been copied
What part of the operating system is loaded into RAM during the boot sequence?
The kernel
What are the six things the kernel performs?
1) Process Management
2) CPU Management
3) Memory Management
4) User Management
5) IO Device Management
6) File System and secondary storage Management
What is a process?
A process is an environment in which a program can execute and is managed independently by the OS
What are the three states a process can be in?
Ready - ready to execute
Wait - waiting for some resource
Active - currently being executed
Difference between single process and multitasking?
Single process - OS grants exclusive use of all unused resources. CPU is often idle waiting for IO
Multitasking - CPU switches rapidly back and forth between different programs using time slicing. Selecting which process to become active is down to the scheduler and dispatcher
What are the three scheduling techniques used?
First-come first-served
Explicit priority
Shortest Remaining Time
What is the difference between the Scheduler and Dispatcher?
Scheduling is the process of deciding which process to make active next, whereas dispatching is the actual task of switching between processes.
What are the three steps the dispatcher makes when switching to another process?
Save registers
Select new process
Restore new process registers
Briefly describe what virtual memory is
Virtual memory makes use of main and secondary memory to make it appear as if there is more memory than there physically is.
This is done by mapping memory addresses in the virtual memory space to physical memory addresses and storing pages of data that is not accessed in memory to secondary memory. When data is requested, it is either retrieved from memory of moved from secondary to main and then retrieved.
