1. Operating System Structure
Introduction of Topics
OS Components
OS Services
System Calls
System Programs
Different types of System Structure
Virtual Machines
System Design and Implementation

2. OS Components Process Management Main-Memory Management
Secondary-Storage Management
I/O System Management
File Management
Protection System
Networking
Command-Interpreter System

3. Process Management Program - static entity Process - active entity
a process is a program in execution with its current values (PC, other registers, variable values, status flags)
Processes require resources (memory, CPU, I/O)
OS is responsible for:
creation/deletion of user and system processes
suspension and resumption of processes
provisions and mechanisms for process synchronization, communication and deadlock handling

4. Main-memory Management
Main memory is generally the only storage that the CPU directly addresses
The OS must provide means for
mapping program logical addresses to memory physical (or absolute) addresses
allocating and deallocating memory for processes
keeping track of which parts of memory are being used by which processes
which processes should be loaded into memory when space becomes available and which processes should be removed when space is needed

5. Secondary-storage and I/O Management
OS is responsible for the following storage activities:
Free-space management
Storage allocation
Disk scheduling
OS is responsible for the following I/O activities:
Device driver communications
Device driver installation
Resource allocation and management

6. File Management
The OS is responsible for the following file activities:
creation/deletion of files
creation/deletion of directories
support of primitives for manipulating files and directories (including editors)
mapping of files onto secondary storage
automatic backup of files

7. Protection Concurrent processes must be protected from each other
processes must gain proper authorization to use/access files, memory, CPU, other resources
memory-addressing hardware ensures that a process can only access its own address space
timer ensures that a process will eventually relinquish the CPU
users are not allowed to directly perform I/O and therefore the OS directly protects against unauthorized I/O

8. Networking
A distributed system is a collection of processors that do not share memory or a clock
Processors communicate to each other through communications lines
high-speed bus, telephone, network lines, etc
OS manages network communications and possibly all network resources depending on the type of network

9. Command-Interpretation
Interface between the user and the OS
Some OS’s have this ability within the OS kernel, others (MS-DOS) use special programs
Modern OS’s use a user-friendly interpreter in the form of a GUI (graphical user interface)
Commands deal with all aspects of the OS

10. OS Services Program execution I/O operations File-system manipulation
Interprocess Communications
Error detection
Resource Allocation
Accounting
Protection/Security

11. System Calls Provide the interface between the program and OS
Available in assembly & machine instruction sets
Might be available in high level languages (like C)
System Calls will require parameters so that the OS can determine specifics
such as what input device should be read from
Three means of parameter passing:
through registers
through a block of memory reserved
through a stack
5 categories of system calls
process control, file manipulation, device manipulation, info maintenance and communications

12. Process Control End or Abort Process initiation
normal vs abnormal termination
includes performing memory dump or process trace
Process initiation
Load, execute, create, terminate
Get and set process attributes
Wait for time or wait for event, signal an event
timer, traps and interrupts
Allocate and free memory for process

13. File and Device Manipulation
Create, delete files
Open, close files
Read, write, reposition file marker
Get or set file attributes
Request device, release device
Read, write, reposition device marker
Get or set device attributes
Logically attach or detach device

14. Information and Communication
Get or set time or date
Get or set system data
Get or set process, file, device attribute
Create or delete communication connection
Send, receive messages
Transfer status information
Attach or detach remote devices

15. System Programs Programming support Program loading Communications
compilers, assemblers, interpreters for common languages
Program loading
loaders, linkers, debuggers
Communications
interprocess communication, user communication
Command-line interpreter
Applications programs
File manipulation
create, delete, copy, rename, print, dump, list
Status information
date, time, available memory, disk capacity, # of users
File modification
editors and others

16. Simple System Structure
OS’s that start small with no well-defined structure but are later enhanced
e.g., MS-DOS or the original Unix)
MS-DOS is essentially a resident system program and device drivers
Original Unix consisted of a kernel and the systems programs where the kernel contained the various device drivers and interfaces)
See figures 3.6 and 3.7, pages 69-70

17. Layered Approaches
A layered approach gives implementers more freedom in the inner workings of a system without affecting the OS or user applications
Overall functionality and features are separated into distinct components
Information hiding and modularity (two fundamentals of programming) can be achieved
Examples include THE OS (figure 3.9) and Venus OS (figure 3.10) pages

18. Virtual Machines Conceptually, a computer is made up of layers:
hardware, kernel, OS, user interface, applications, user
A virtual machine can be created by allowing applications programs to directly call and control systems programs
The application programs view everything underneath them as part of the hardware which allows for a uniform interface among all components
This allows for easy:
Multitasking
Virtual Memory
File handling is a problem

19. Benefits of VM implementation
Environment is protected from system resources
No security problems (VM is isolated)
Useful for OS research and development
Allows for emulation of other types of machines (e.g., running MS-DOS on a Sun workstation or Windows on a Macintosh)

20. Java
Java is implemented by a compiler that generates bytecode output which are instructions that run on a Java VM
Each platform (IBM, Mac, Sun, etc…) has its own JVM implementation (the JVM is actually an interpreter)
This allows source code to be transported over the internet and executed no matter what the machine is
Has built-in security to disallow unsafe and unsecure operations

21. OS Design and Implementation
Design Goals - type of OS - batch, time-shared, single- vs multi-user, distributed, real-time, etc...
Mechanisms and Policies - separation of how things will be done and what will be done
Implementation - assembly language, C, lisp
Generation - configuration of the OS to the hardware -- what CPU will be used? how much memory is available? what devices are available?