Lecture 1 - Introduction to Operating Systems¶

1.0 A bit of history¶

Father of Linux - Linus Torvalds (at age 21)
LLVM - Low Level Virtual Machine by Chris Lattner
Ubuntu - Linux Core Plus GNU
Unix - Multitasking, multi-user OS

1.1 What is an Operating System?¶

An operating system is a software that acts as an intermediary between the computer hardware and the user. It provides an environment in which a user can execute programs conveniently and efficiently.

Resource Abstractor and Allocator

Starting an OS¶

The first program that runs when a computer starts up is the bootloader -- the bootstrap program initializes the computer.
Locates and loads the OS kernel into memory
Wait for 'event' to occur

Multi-programming¶

Multi-programming with rapid context switching -- Actually not working all the same time.
jobs are called processes

The running OS¶

The kernel is not a running job -- It's code that resides in memory and is ready to be executed at any moment
OS be executed on behalf of a job whenever requested
OS do special/dangerous things that user programs can't do
When designing a kernel : Lean and Mean
Lean - Only the necessary features
Mean - single minded, focused on the job
Size of Linux Kernel when loaded in memory is about x MBs to xx MBs
No memory protection with the kernel
The kernel's the one saying to a process "segmentation fault"
Nobody's watching over the kernel

Designing an OS¶

Design CPU to support OS
User / Kernel mode -- add a 'mode bit'
User mode - restricted mode
Kernel mode - unrestricted mode

------------------------------------
| APP --> Unprivileged instructions |
------------------------------------
| OS --> Privileged instructions    |
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|  Hardware                         |
------------------------------------

OS Events¶

An event stops execution, changes mode, and changes context

System Call - Request to the OS

System Calls¶

When a user program need sto do something privileged, it makes a system call

A special kind of trap
Every ISA provides a system call instruction that
Causes a trap,which maps to a kernel handler

Timers¶

The timer interrupts the computer regularly

The OS always makes sure the timer is set before turning over control to user code

A process is a program in execution¶

Program: passive entity
Process: active entity

The OS is responsible for :

Creating and deleting processes

Suspending and resuming processes

Providing mechanisms for process synchronization

Providing mechanisms for process communication

Providing mechanisms for deadlock handling

最后更新: 2024年9月30日 11:27:07
创建日期: 2023年11月11日 10:26:46