1. Course Overview Introduction Computer System Structures
Operating System Structures
Processes
Process Synchronization
Deadlocks
CPU Scheduling
Memory Management
Virtual Memory
File Management
Security
Networking
Distributed Systems
Case Studies
Conclusions

2. Chapter Overview Operating System Structures
Motivation
Objectives
OS Components
OS Services
System Calls
System Programs
OS Structure
Kernel
Virtual Machines
Characteristics of Modern Operating Systems
Important Concepts and Terms
Chapter Summary

3. Motivation
to understand the functioning of an operating system, it is important to have an overall view of it
many components can’t considered in isolation because they interact with and depend on each other
different design approaches are possible with different underlying hardware capabilities

4. Objectives get to know the important components of an operating system
understand the interrelationships between the components
identify different approaches to the overall design of operating systems
be aware of current trends in operating system design

5. OS Components process management main memory management
secondary storage management
file management
I/O system management
networking
protection
user interface

6. OS Services program execution I/O operations
file and directory services
communication
error detection and handling
resource allocation
protection
accounting

7. Producing an Executable.
Source Code
Object File
Executable
Compile
Link
Libraries and
other Object files
[David Jones

8. System Calls interface between processes and operating system
used to request services from the OS
provides operations on objects that processes can not or are not allowed to handle directly
used by programmers, not by users
types of system calls
process control
file manipulation
device manipulation
information maintenance
communications

9. System Calls Functions supplied by system libraries.
These functions will contain a
trap instruction.
#include <sys/types.h>
#include <dirent.h>
#include "ourhdr.h"
int main(int argc, char *argv[]) {
DIR *dp;
struct dirent *dirp;
if (argc != 2)
err_quit("a single argument (the directory name) is required");
if ( (dp = opendir(argv[1])) == NULL)
err_sys("can't open %s", argv[1]);
while ( (dirp = readdir(dp)) != NULL)
printf("%s\n", dirp->d_name);
closedir(dp);
exit(0); }
[David Jones]

10. Interrupt Handling Main Memory User Mode 1. Program performs trap
User Program #2
1. Program performs trap
2. OS determines service
number
3. Service is located and
executed.
4. Control returns to user
program.
User Program #1
Main Memory
trap 002 4 1 3
Based on a diagram from
“Modern Operating Systems” by
Andrew Tanenbaum. 2
System/Kernel Mode
Kernel
[David Jones]

11. System Programs
programs providing more convenient functions to utilize the system
directly accessible by the user
types of system programs
file manipulation and modification
programming environments
communication
status information
command interpreter

12. OS Structure monolithic approach layered approach
the whole OS is one large program
often used under resource constraints (processing power, memory space)
example: PC DOS
layered approach
functionalities are grouped into layers from hardware to user programs
better separation of functions
example: OS

13. Kernel
core part of the operating system comprising the minimal set of functionalities
process dispatching
basic memory management
interprocess communication
protection
is always kept in main memory
porting is made easier

14. Virtual Machines software abstraction by the OS
provides an interface identical to the corresponding hardware
emulates different hardware architectures on the same hardware
isolates users, programs, and processes from each other
example: Java Virtual Machine

15. Characteristics of Modern Operating Systems
microkernel architecture
multithreading
symmetric multiprocessing
distributed operating systems
object-oriented design

16. Microkernel Architecture
kernel contains only a few essential functions
address spaces, interprocess communication, basic scheduling
the kernel must be adapted to a specific hardware
server processes provide the remaining functionality in the form of services
services can be offered by local or remote server processes
flexible approach, especially for distributed systems
previous architectures: large, monolithic kernel includes most of the OS functionality

17. Multithreading an application is executed by one or more processes
each process may be divided into threads
threads are the basic unit of work in an OS
threads are also known as lightweight processes
switching between threads is simpler than between processes
the general treatment of threads and processes by the OS is essentially the same
a thread shares resources with its peers
good for the modularity of applications
allows modules to execute largely independently

18. Symmetric Multiprocessing
provides more processing power through multiple processing elements
the processes share main memory and I/O devices
the processors are either identical, or can at least perform the same functions

19. Distributed Operating Systems
all resources within the distributed system are available to all processes if they have the right permissions
the execution of tasks can be distributed over several nodes
there is one single file system encompassing all files on all nodes

20. Object-Oriented Design
development method for modular systems
the interface of modules is independent of the actual implementation
internal details of modules are not accessible to others
goes well with the microkernel method and distributed systems

21. OS Design Goals user perspective system perspective
convenient, responsive, easy to use, reliable, safe, fast
system perspective
efficient, flexible, reliable, easy to design, implement, and maintain
difficult task, requires many tradeoffs

22. Microkernel OS Applications Operating System Micro-Kernel Hardware CPU
Main Memory
I/O Devices
System Bus
Control Unit
Registers
Arithmetic Logic
Unit (ALU)
Controllers
Hardware
[David Jones

23. Microkernel OS Applications Server Processes Operating System
Services
File System
Device
Drivers
Personalities
Operating
System
Micro-Kernel
CPU
Main Memory
I/O Devices
System Bus
Control Unit
Registers
Arithmetic Logic
Unit (ALU)
Controllers
Hardware
[David Jones

24. Microkernel OS Microkernel OS Applications Users and User Programs
Server Processes
Personalities
System
Services
Device
Drivers
File System
Operating
System
Micro-Kernel
CPU
Main Memory
I/O Devices
System Bus
Control Unit
Registers
Arithmetic Logic
Unit (ALU)
Controllers
Hardware
[David Jones

25. Distributed OS Applications Users and User Programs Server Processes
Personalities
System
Services
Device
Drivers
File System
Operating
System
Micro-
Kernel
Computer
Node
Micro-
Kernel
Computer
Node
Micro-
Kernel
Computer
Node
Micro-
Kernel
Computer
Node
Micro-
Kernel
Computer
Node
Micro-
Kernel
Computer
Node
Hardware
[David Jones

26. Future Operating Systems
micro-kernel based
multiple personalities
emulate appearance and functionality of existing OSes
distributed systems

27. OS Structure Examples
MS-DOS & Windows
Windows NT
Unix

28. MS-DOS & Windows Structure
originally (DOS 1) monolithic due to space and processing power restrictions (Intel 8086, 8 KBytes main memory)
slow incorporation of advanced concepts
hard disk, hierarchical file systems, I/O redirection, background printing, networking, ...
fresh start with Windows NT
single-user, multitasking
designed for 32-bit microprocessors (Intel Pentium)

29. Windows NT Structure hardware abstraction layer (HAL) microkernel
provides adaptation to the underlying hardware through a generic hardware interface
microkernel
thread scheduling, process switching, exception handling (interrupts), multiprocessor synchronization
executive services
modules for system functions
I/O manager, object manager, process manager, virtual memory manager, security reference monitor, windows modules
system services
interface to software running in user mode

30. Hardware Abstraction Layer (HAL)
Windows NT Structure
Microkernel OS
Users and
User Programs
Applications and
User Interface
POSIX
Subsystem
Win32
Subsystem
OS/2
Subsystem
Security
Subsystem
System Services
Local
Procedure
Call
Facility
I/O
Manager
Object
Manager
Security
Reference
Monitor
Process
Manager
Virtual
Memory
Manager
Window
Manager
Windows NT
Executive
Cache
Manager
File System
Drivers
Micro-Kernel
Graphic
Device
Drivers
Network
Drivers
Hardware Abstraction Layer (HAL)
Device
Drivers
Hardware
[Stallings 98]

31. Unix Structure single processor, multi-user, multitasking system
portable through implementation in a high-level language (C), in contrast to assembly language
relatively large, non-modular kernel
access to kernel functions through system calls
shells as user interface, GUI (XWindows) added later
modern Unix variants have been redesigned around microkernel

32. Modern Unix Kernel Common Facilities a.out elf exec switch file
mappings
NFS
device
mappings
virtual
memory
framework
vnode/vfs
interface
FFS
RFS
anonymous
mappings
Common
Facilities
time-sharing
processes
block
device
switch
scheduler
framework
disk
driver
system
processes
tape
driver
Streams
network
driver
tty
driver
[Stallings 98]

33. Important Concepts and Terms
command interpreter
communication
device management
directory system
distributed system
file system
interrupt
kernel
layered structure
memory management
microkernel
monolithic structure
multiprocessing
multiprogramming
multitasking
operating system
process
process control block (PCB)
process management
protection
resource allocation
secondary storage management
shell
system call
system program
task
thread
time-sharing
user interface
virtual machine

34. Chapter Summary
the operating system provides services and manages resources
user processes request services from the OS through system calls
protection, resource management, abstraction
modern operating systems separate functions into modules
layered approach, microkernel, object-oriented, virtual machine