1. CS U480: Systems & Networks 1. Introduction Donghui Zhang

2. Syllabus Instructor: Donghui Zhang
Class page linked from my home page:

3. Your Background CSU380: Computer organization C/C++ programming
System architecture: Processors, memory, I/O devices
Processor architecture: ALU, instruction execution
Assembly-level programming
C/C++ programming
Familiarity with the C language and the standard C library
Please consult with me if you are unsure your background is sufficient

4. Why Programming For CS: must. For IS: also important.
A pilot must know how to fly an airplane.
For IS: also important.
A project manager needs to have technical background.
Bill Gates used to be a superb programmer.
Guest speaker: Prof. Hafner.

5. Why C (and not Java) Talked with Mr. Feuer and Prof. Hafner.
We provide guidance to what you should learn. (If you say “give us A without any exam or project”…)
Most OS are implemented in C.
Java hides many low-level details.
This is a place to strengthen your C skills.

6. What is an Operating System?
An operating system is a program that acts as an intermediary between a user of a computer and the computer hardware.
Goals:
Execute user programs and make solving user problems easier.
Make the computer system convenient to use.
Performance measures:
Throughput: The total amount of work done over a period of time.
Turnaround: The total time it takes to complete a job.

7. Concept Map Applications GUI Console OS CPU ALU Registers Memory
Peripherals
Disks
Keyboard
Mouse
Display

8. Software Layers Application c = getc() Library read(…)
Operating System kb_driver_read(…)
Device driver
read_device(…)

9. Compilation vs. Execution
During compilation, statements in higher-level languages are converted into machine code
During execution, machine code is interpreted by a processor
Memory
Compiler
High-level language program
Assembly language
Assembler
Machine code
Link editor
Libraries of
Executable
Shared
Libraries
Operating
System
Device
Drivers

10. Evolution of the OS In the beginning
Whirlwind at MIT
PDP-1 from DEC
Altair from MITS
Program stored in a hardware patch board or toggled in using switches
Program can access all of memory
Program starts at location zero
Loading programs by hand is slow and error-prone and painful, so . . . n
Program
Memory

11. Evolution of the OS: The Loader
Create a very short program to load longer programs
Toggle in bootstrap loader
Primitive loader may load in program or a more complex loader to read from cards or tape
Loading from cards is very slow, often took longer to load than to run, wasting (expensive) processor cycles, so . . . n
Loader
Program
Memory

12. Evolution of the OS: Batch Processing
Batch Loader
Jobs are spooled on tape
While one batch of jobs is running, card reader writes next batch of jobs on tape
Jobs are read sequentially from tape into memory
Tape is still relatively slow compared to processing
Program
Memory

13. The Concept of a Job
With the introduction of programming languages, a translator is needed to convert a program into machine code
When a program is stored on cards in the programming language, e.g., assembler or Fortran, it must be translated before it can be run
Example: To run a program written in Fortran
Load (machine code for) Fortran compiler
Run compiler:
Compiler reads program, writes machine code
Load (machine code for) program
Run program

14. Evolution of the OS: Multiprogramming
Load next program while previous program is running
But now both programs can’t begin at address zero (in fact, starting address isn’t known in advance)
Solutions?
Programs that perform lots of I/O waste (expensive) processor cycles n
Loader
Program 2
Program 1
Memory

15. Evolution of the OS: Multitasking
Share execution time among programs
When one program starts I/O, let the other run.
What is needed to switch from one program to another?
A program bug in one program can overwrite another program, or the system programs and data, so . . . n
Loader + scheduler
System data
Program 2
Program 1
Memory

16. Evolution of the OS: Protection
Run programs in separate address spaces
System programs need to cross address spaces.
System runs in privileged mode.
The more programs in memory, the less memory available for each program, so . . .
Memory
Loader, scheduler, memory mgr
Program 1
Program 2
System data
Program 3 n

17. Evolution of the OS: Virtual Memory
Address space implemented in both main and secondary memory
Broken into pages
A program’s address space is a set of pages.
The address space for a program may be larger than main memory!
Pages are swapped in and out of main memory as needed.
Memory
Loader, scheduler, memory mgr, resource mgr
Disk n

18. OS Diversity Great diversity of programmable hardware
Super computers: simulation, scene generation, data mining
Servers: database, web, video
Personal: desktop, laptop
Embedded: PDA, phone, media device
Nature of the OS depends on
Application mix
Hardware capability
Real-time requirements
With the proliferation of embedded systems, most processors do not run a general purpose OS

19. OSes are complex programs developed over many years by many people
They confront common problems that reappear in other contexts
The problems have been formalized
A variety of solutions have been proposed and implemented
Choosing a solution requires evaluating tradeoffs of space, time, and complexity
OSes are a rich source of well-designed sample programs
We will study OSes by exploring common components
Understand the motivation for each component
Understand the tradeoffs for each implementation

20. Common System Components
Process Management
Main-Memory Management
File System
I/O System
Network Management
Let’s take a high-level tour of these components

21. Process Management A process is a program in execution
To accomplish its task, a process needs certain resources:
CPU time
Memory
Files
I/O devices.
The OS is responsible for the following activities in connection with processes:
Process creation and deletion
Process suspension and resumption
Mechanisms for:
Process synchronization
Inter-process communication

22. From Program to Process
Memory
Compiler
High-level language program
Assembly language
Assembler
Machine code
Link editor
Libraries of
Executable
Shared
Libraries
Operating
System
Device
Drivers

23. Memory Management Main memory is a large array of words
Each word (or, often byte) has its own address
Data in memory is shared by the CPU and I/O devices
Main memory is (usually) volatile
It loses its contents in the case of system failure.
The OS is responsible for the following activities in connection with memory management:
Keep track of which parts of memory are currently being used and by whom.
Decide which processes to load when memory space becomes available.
Allocate and deallocate memory space as needed.

24. Memory Management (cont.)
Loader, scheduler, memory mgr
Program 1
Program 2
System data
Program 3 n

25. Secondary-Storage Management
Secondary storage is (usually) a large array of blocks
Each block has its own address
Data is moved between main memory and secondary storage in units of blocks
Secondary storage is non-volatile and can be very large
Disks are the most common in general purpose systems
Memory cards and stick are common on portable devices
The OS is responsible for the following activities in connection with secondary storage management:
Free space management
Storage allocation
For disks, scheduling of block transfers

26. Secondary-Storage Management (cont.)
Memory
Loader, scheduler, memory mgr, resource mgr
Disk n

27. File Management A file is a collection of related information
Files are stored within a file system
From the view of most systems, a file is an array of bytes
The OS is responsible for the following activities in connections with file management:
File creation and deletion
Directory creation and deletion
Support of primitives for manipulating files and directories
Mapping files onto secondary storage.
File backup on stable (nonvolatile) storage media

28. I/O System Management
Input/Output refers to the movement of data between main memory and peripheral devices
Devices vary widely in their operation and behavior
Devices are partitioned into classes to factor common behavior
A device driver translates between general OS operations and device-specific commands
I/O managements consists of
A buffer-caching system
A general device-driver interface
Drivers for specific hardware devices

29. I/O System Management (cont.)

30. Network Management
Networking allows distinct computer systems to exchange data
Communication takes place using a protocol
Networked computers vary widely in their degree of coupling:
They may share a common OS and processes may be visible across systems
They may share nothing except a communication port
Networking allows users to access to non-local resources, allowing:
Computation speed-up, through special purpose hardware or parallel processing
Availability of data from other systems
Enhanced reliability through redundancy

31. Network Management (cont.)