1. Operating Systems CMPSCI 377 Lecture 1
Emery Berger
University of Massachusetts, Amherst

2. Information Course web page:
My contact info:
Phone:
Office hours by appointment
TA’s:
Gene Novark, Louis Theran
Discussion section:
W 12:20 – 1:10, Hasbrouck 138

3. Today’s Class Administrivia:
Course organization & outline
Prerequisites & course sign-up
Introduction & History of Operating Systems

4. Course Organization Capacity is 50 Class: junior or senior-level
Not for freshman or sophomores
Enrollment policy
If space becomes an issue, graduating seniors get preference

5. Prerequisites CMPSCI 187 (Data Structures) CMPSCI 201 (Architecture)
Textbook:
Operating Systems (Deitel, Deitel & Choffnes)

6. Course Requirements
Class participation: 10% (includes in-class quizzes)
Homework: 10%
Programming projects: 40%
Exams (two in-class, one final): 40%
Programming assignments: Java
Strict late policy – not accepted late
Cheaters will be found and punished
Will use sophisticated software to detect plagiarized programs

7. Course Organization Accounts in EdLab: 30+ Linux PC’s
Discussion section to help you with lab assignments
Office hours and location of TA’s:
Gene Novark: to be announced
Louis Theran: to be announced

8. Introduction to Operating Systems
What’s an operating system? (OS)
Why are OS’s important?
Historical perspective on operating systems

9. What’s An Operating System?
Definition has changed over years
Originally, very bare bones
Now, includes more and more
Bill Gates: Windows =
Everything in other operating systems
Internet Explorer
Media player
“even a ham sandwich” (DOJ vs. Microsoft)

10. OS: More Traditional View
Interface between user and architecture
Hides architectural details
Implements virtual machine:
Easier to program than raw hardware (hopefully)
Provides services and coordinates machine activities
User-level Applications
virtual machine interface
Operating System
physical machine interface
Hardware

11. Operating Systems: Key Features
Provides standard services (interface) that hardware implements
File system, virtual memory, networking, scheduling, time-sharing…
Coordinates multiple applications and users to achieve safety, fairness and efficiency (high throughput)
Concurrency, memory protection, networking, security
OS design challenges: convenient and efficient
Software engineering & systems engineering problems

12. Introduction to Operating Systems
What’s an operating system? (OS)
Why are OS’s important?
Historical perspective on operating systems

13. Importance of Operating Systems
Key component of computer systems
Meeting point of software & hardware
Understanding how computers work = understanding operating systems
OS provides key services required by all application programs
Rich topic:
OS = most complex software on your PC
Windows XP kernel: 40 million lines of code

14. Why So Complex? Provides high-level of abstraction
Illusion of:
Infinite memory
Complete control of resources
Requires sophisticated system design:
Tradeoffs:
Performance vs. convenience (OS abstractions)
Performance vs. simplicity (OS design)
Putting functionality in hardware vs. software
As systems changes, OS must adapt (new hardware, software)

15. New Developments in OS Design
Operating systems: very active field of research
Demands on OS’s growing
New application spaces (Web, Grid)
Rapidly evolving hardware
Advent of open-source operating systems – Linux
You can contribute to and develop OS’s!
Excellent research platform

16. Background You Need OS: software that manages hardware Hardware:
Must understand both
Hardware:
CPU: instruction sets, memory hierarchies
I/O systems
Software:
Complex data structures
Object-oriented programming (esp. for encapsulation)
Java (although…)

17. Introduction to Operating Systems
What’s an operating system? (OS)
Why are OS’s important?
Historical perspective on operating systems

18. The Dark Ages (1940’s-1960’s) Hardware: expensive; humans: cheap
Evolution of functionality:
One user
Batch processing
Overlap of I/O & computation
Multiprogramming

19. 1. Single-User Computers
One user at a time on console
Computer executes one function at a time
No overlap: computation & I/O
User must be at console to debug
Multiple users = inefficient use of machine

20. 2. Batch Processing Execute multiple “jobs” in batch:
Load program
Run
Print results, dump machine state
Repeat
Users submit jobs (on cards or tape)
Human schedules jobs
Operating system loads & runs jobs
More efficient use of machine, complicates debugging

21. 3. Overlap I/O and Computation
Before: machine waits for I/O
New approach:
Allow CPU to execute while waiting
Add buffering, interrupt handling
More efficient use of machine, but still one job at a time

22. 4. Multiprogramming Allow several programs to run at same time
Run one job until I/O
Run another job, etc.
OS manages interaction between programs:
Which jobs to start
Protects program’s memory from others
Decides which to resume when CPU available

23. OS Complexity Increased functionality & complexity First OS failures
Multics (GE & MIT): announced 1963, released 1969
OS/360 released with 1000 known bugs
Need to treat OS design scientifically
Managing complexity becomes key to…

24. The Renaissance (1970’s) Hardware: cheap; humans: expensive
Users share system via terminals
The UNIX era
Multics:
army of programmers, six years
UNIX:
three guys, two years
“Shell”: composable commands
No distinction between programs & data
But: response time & thrashing

25. The Industrial Revolution (1980’s)
Hardware very cheap;
humans expensive
Widespread use of PCs
IBM PC: 1981, Macintosh: 1984
Simple OS (DOS, MacOS)
No multiprogramming, concurrency, memory protection, virtual memory, …
Later: networking, file-sharing, remote printing…
GUI added to OS (“WIMP”)

26. The Modern Era (1990’s-now)
Hardware cheap; Processing demands increasing
“Real” operating systems on PC’s
NT (1991); Mac OS X; Linux
Different modalities:
Parallel: Multiple processors, one machine
Distributed: Multiple networked processors
Real-time: Strict or loose deadlines
Sensor networks: Many small computers

27. Moral of the Story The only constant: Change
In 50 years, almost every computer component now 9 orders of magnitude faster, larger, cheaper
Example:
1983
1999
MIPS
0.5
500
cost/MIP
$100,000
$500
memory
1 MB
1 GB
network
10 Mbit/s
1 GB/s
disk
1 Tbyte

28. Moral of the Story, II
No counterpart in any other sphere of human existence!
Transportation:
200 years to go from horseback (10 mph) to Concorde (1000 mph) = 2 orders of magnitude
Communication is closest:
100 years to go from Pony Express (10 mph) to nearly speed of light (600 million mph) = 7 orders of magnitude
And operating systems must adapt…

29. Next Time
Operating Systems & Architecture
Work on Lab 1!