第一课 笔记
Goal:
. What is an Operating System? And what is it not?
. Examples of OS design
. Why study OS?
. How does this class operate?
** Interactive is important! **
Ask Questions!
#为何要学习OS？
底层组件越来越多
设备越来越多
软件复杂度不断攀升（30行代码一个bug，一个月？）
The latency is not change
Heat is a major problem
*Complexity
. How to manage complexity at all levels?
. Many issues and many tradeoffs
. Need a global view of systems(decompose into components)
. Need a global understanding of systems(applications, networks, databases, os, security, software engineering...)
Examples: some Mars Rover Requirements
- 20Mhz powerPC processor, 128MB of RAM
- cameras, scientific instruments, batteries, solar panels, and locamotion equipment
- Many independent processes work together
- Can't hit reset button very easilly
- Must reboot itself if necessary
- Always able to receive commands from Earth.
- Individual programs must not interfere
- Suppose the MUT(Martion Universal Translator Module) buggy
- Better not crash antenna positioning software
- Aall software may crash accasionally
- Automatic restart with diagnostics sent to Earth
- Periodic checkpoint of results saved?
- Certain functions time critical
-Nee to stop before hitting something
- Must track orbit of Earth for communication
How do we tame complexity?
# Every piece of computer hardware different
- Different CPU
- Different amount of meory, disk
- Different types of devices
- Different networking environment
Questions:
- Does the programmer need to write a single program that performs many idependent activities?
- Does every program have to be altered for every piece of hardware?
- Does a faulty program crash everything?
- Does every program have access to all hardware?
OS Tool: Virtual Machine Abstraction
Application
----------------------------- Virtual Machine Interface
Operating System
----------------------------- Physical Machine Interface
Hardware
#Software Engineering Problem:
- Trun hardware/software quirks (what programmers want/need)
- Optimize for convenience, utilization, security, reliability, etc...
# For any OS area (e.g. file systems, virtual memory, networking, scheduling)
- What's the hardware interface? (physical reality)
- What's the application interfaces (nicer abstraction)
Software
******** instruction set *********
hardware
# Why do interfaces look the way that the do?
- History, Functionality, Stupidity, Bugs, Mangement
- CS152 => Machine interface
- CS160 => Human interface
- Cs169 => Software engineering/management
# Should responsibilities be pushed across boundaries?
- RISC architectures, Graphical Pipelien Architecture
Course Website:
http://inst.eecs.berkeley.edu/~cs162/fa08/Webcast/Podcast:
http://webcast.berkeley.edu/courses/index.phpNewsgroup: ucb.class.cs162 (use authnews.berkeley.edu)
Text book: Operating System Concepts, 7th Edition Silbershatz, Golvin, Gogne
Topic Coverage
1 week Fundamentals (OS structures)
1.5 weeks Process Central and Threads
2.5 weeks Synchronization and scheduling
2 weeks Protection, Address translation, Caching
1 week Demand Pagine
1 week File Systems
2.5 weeks Networking and Distributed Systems
1 week Protection and Security
1 week Software Engineering
?? Advanced topics
Grading
# Rough Grade Breakdown
-Two Midterms: 15% each
One Final: 15%
Four Projects: 50% (i.e 12.5% each)
Participation: 5%
# Four Projects:
- Phase I: Build a thread system
- Phase II: Implement Multithreading
- Phase III:Caching and Virtual Memory
- Phase IV: Parallel and Distributed Systems
#Late Policy:
- Each group has 5 "slip" days
- Far Projects, slip days deducted from all partners
- 10% off per day after slip days exhausted
Group Project Simulates Industrial Environment
# Project teams have 4 or 5 memebers in same discussion section
- Must work in groups in "the real world"
# Communicate with colleagues (team members)
- Communication problems are natural
- What have you done?
- What answers you need from others?
- You must document your work!!!!
- Everyone must keep on on-line notebook
# Communicate with supervisor(TAs)
- How is the team's plan?
- Short progress reports are required:
> What's the team's game plan?
> What is each member's responsibility?
# Typical Lecture Format
Attention: (minutes) 20m25m25m"In Conclusion,..."
1 -Minute Review
20-Minute Lecture
5 -Minute Administrative Matters
25-Minute Lecture
5 -Minute break(water, stretch)
25-Minute lecture
Instructor will come to class early & stay after the answer questions
(44 Minute)
Virtual Machines
# Software emulation of an abstract machine
- Make it look like hardware has features you want
- Programs from one hardware & OS on another one
# Programming simplicity
- Each process thinks it has all memory/CPU time
- Each process thinks it owns all devices
- Different Devices appear to have same interface
- Device Interfaces more powerful than raw hardware
> Bitmapped display => windowing system
> Ethernet card => reliable, ordered, networking(TCP/IP)
# Fault Isolation
- Processes unable to directly impact other processes
- Bugs cannot crash whole machine
# Protection and Portability
- Java interface safe and stable across many platforms
Four Components of a Computer System
Hardware, Operating System, Application, User
Definition: An operating system implements a virtual machine that is (hopefully) easier and safer to program and use than the raw hardware.
What does an Operating System do?
# Silerschatz and Govin:
"An OS is simplilar to a government"
- Begs the question: does a government do anything useful by itself?
# Coordinator and Traffic Cop
- Manages all resources
- Settles conflicting requests for resources
- Prevent errors and improper use of the computer
- Facilitator:
Provides facilities that everone needs
Standard Libraries, Windowing systems
Make application programming easier, faster, less error-prone
# Some fetures reflect both tasks
- E.g. File Sstem is needed by everone (Facilitator)
- But File system must be protected (Traffic Cop)
What is an Operating System, ... Really?
# Most Likely:
- Memory Management
- I/O Management
- CPU Scheduling
- Communications? (Does Email belong in OS?)
- Multitasking/multiprogramming?
#What about?
- File System?
- Multimedia Support?
- User Interfaces?
- Internet Browser?
#Is this only interesting to Academics??
# No universally accepted definition
# "Everything a vendor ships when you order an operating system" is good approximation
- But varies widly
#"The one program running at all times on the computer" is the kernel.
- Everything else is either a system program (ships with the operating system) or an application program
What if we didn't have an OS
# Source code => compiler => object code => hardware
#How do you get object code onto the hardware?
#How do you print out the answer?
#Once upon a time, had to toggle in program in binary and read out answer from LED's!
Simple OS: what if only one application
#Examples:
- Very early computers
- Early PCs
- Embedded controllers(elevators, cars, etc)
# OS becomes just a library of standard services
- Standard device drivers
- Interrupt handlers
- Math library
(MS-Dos)
#What about Cell-phones, Xboxes, etc?
- Is this organization enough?
# Can OS be encoded in ROM/Flash ROM?
# Does OS have to be software?
-Can it be hardware?
-Custom chip with predefined behavior
-Are these even OSs?
More complex OS: Multiple Apps
# Full coordination and protection
- Manage interactions between different users
-Multiple programs running simultaneously
- Multiplex and protect Hardware resources
> CPU, Memory, I/O devices like disks, printers, etc
Example: Protecting processes from each other
#Problem: run multiple application in such a way that they are protected from one another
#Goal:
- Keep User Programs form Crashing OS
- Keep User Programs from Crashing each other
- [Keep parts of OS form crashing other parts?]
# (Some of the required) Mechanisms:
- Address Translation
- Dual Mode Operation
# Simple policy:
- Programs are not allowed to read/write memory of other programs or of Operating System
#Address Space
- A groups of memory addresses usable by something
- Each program (process) and kernel has potentially different address spaces.
#Address Translation:
- Translate from Virtual Addresses (emitted by CPU) into Physical Addresses(of memory)
- Mapping often performed in hardware by Memory Management Unit(MMU)
Virtual Addresses Physical Address
CPU ---------------------> MMU ---------------------> RAM HW
Address translation
Dual Mode Operation
#Hardware provides at least two modes:
- "Kernel" mode (or "supervisor" or "protected")
- "User" mode: Normal programs executed
User Mode --> system calls --->User Mode
| |
kernel mode ----------
# Some instructions/ops prohibited in user mode:
- Example: cannot modify page tables in user mode
> attempt to modify => exception generated
# Transitions from user mode to kernel mode:
- System calls, interrupts, other exeptions
OS Systems Principles
#OS as illusionist:
- Make hardware limitatins go away
- Provide issulsion of dedicated machine with infinite memory and infinite processors
# OS as government:
- Protect users from each other
- Allocate resources efficiently and fairly
# OS as complex system
- Constant tension between simplicity and functionality or performance
# OS as history teacher
- Learn form past
- Adopt as hardware tradeoffs change
Why Study Operating Systems
# Lear how to build complex systems
- How can you manage complexity for future projects?
# Engineering issues
- Why is the web so slow sometimes? Can you fix it?
- What features should be in the next mars Rover?
- How do large distributed system work? (Kazoo, etc)
# Buying and using a personal computer
- Why different PCs with same CPU behave differently
- How to choose a processor (Opteron, Itanium, Celeron, Pentium, Hexium)? [Ok, made last one up]
- Shoulw you get Windows XP, Vista, Linux, Mac OS...?
- Why does Microsoft have such a bad name?
#Business issues:
- Should your division buy thin=clients vs PC?
#Security, viruses, and worms
- What exposure do you have to worry about?
"In conclusion"
# OS provide a virtual machine abstraction to handle diverse hardware
# OS coordinate resources and protect users from each other
# OS simplify application development by providingn standard services
# OS can provide an array of fault containment, fault tolerance, and fault recovery
