Operating Sysems Study Guide

Operating Systems I Mid-­term Review and Study Guide Basic Concepts:

What is an operating system?

A program that acts as an intermediary between a user of a computer and the computer hardware

- basic functions?

1.) OS is a resource allocator

2.) manages all resources

3.) decides between conflicting requests for efficient and fair resource use

4.) OS is a control program

5.) controls execution of programs to prevent errors and improper use of the

computer

6.) a program running at all times on the computer, usually called the kernel

7.)everything else is either a

a.) system program: associated with the OS but not part of the kernel

b.) application program: not associated with the OS

user/kernel modes of operation?

1.) The operating system must ensure correct operation of the computer system. To prevent user programs from interfering with the proper operation of the system, the hardware has two modes: user mode and kernel mode. Various instructions (such as I/0 instructions and halt instructions) are privileged and can be executed only in kernel mode.

2.) Kernel Mode

In Kernel mode, the executing code has complete and unrestricted access to the underlying hardware. It can execute any CPU instruction and reference any memory address. Kernel mode is generally reserved for the lowest-level, most trusted functions of the operating system. Crashes in kernel mode are catastrophic; they will halt the entire PC.

3.) User Mode

In User mode, the executing code has no ability to directly access hardware or reference memory. Code running in user mode must delegate to system APIs to access hardware or memory. Due to the protection afforded by this sort of isolation, crashes in user mode are always recoverable. Most of the code running on your computer will execute in user mode.

-services it provides?

1.) CPU moves data from/to main memory to/from local buffers

2.) I/O is from the device to local buffer of controller

3.) Helpful...