1. OS Organization

2. Basic OS Responsibilities
Create an abstract machine environment
A nicer environment than bare hardware
Consists of multiple, autonomous abstract components
Components may be in use concurrently
Coordinate the use of the components
Resource manager
Manage according to the policies of the machine’s administrator

3. Basic OS Functions
Exact set of functions required depends on engineering and marketing choices but each function falls in one of these categories:
Device management
Process, thread, and resource management
Memory management
File management

4. Basic OS Organization Processor(s) Main Memory Devices
Process, Thread &
Resource Manager
Memory
Manager
Device
File

5. Device Management
OS uses policies chosen by designer or system administrator to manage
Allocation
Isolation
Sharing
Device manager in two parts
Device independent – provides unified interface
Device dependent – device driver: handles those aspects unique to a device

6. Device Management – cont.
Device-Independent
Part
Device-Dependent
Device …

7. Device Management – cont.
Application
Process
File
Manager
Device Controller
Command
Status
Data
Hardware Interface
System Interface
Device-Independent
Device-Dependent

8. Device Management – cont.
read(device, …); 9 1 8b
Data
System Interface
Device Status Table 4 7
Device
Handler
read driver 2
write driver 6 8a
Interrupt
Handler 3
Hardware Interface 5
Command
Status
Data
Device Controller

9. Device Management – cont.

10. Life Cycle of an I/O Request

11. Process Management Process Protection Description Deadlock
Process Mgr
Protection
Deadlock
Synchronization
Resource
Manager
Resource
Manager
Resource
Manager
Scheduler
CPU
Other H/W

12. Process, Thread, and Resource Management…
Processor
Primary
Memory
Abstract
Resources
Multiprogramming
Thread
Abstraction
Process
Generic
Resource
Manager
Other

13. Memory Management Process Manager Primary Memory Block Allocation
Virtual
Isolation &
Sharing
Storage
Devices

14. Memory Management – cont.

15. Memory Management – cont.

16. Memory Management – cont.

17. File System Management

18. Basic OS Functions Scheduler IPC Process/Thread Admin Synchronization
Memory
Allocation
Virtual
File
Management
Device
Resource
Deadlock
Protection
Mechanisms
Interrupt
Handler

19. OS Design (a) Monolithic (b) Modular (c) Extensible (microkernel)
Application
Software
Other System
Other OS Functions
Kernel Functions
Nucleus Functions
Skeletal Nucleus
(a) Monolithic
(b) Modular
(c) Extensible
(microkernel)
(d) Layered

20. Implementation Issues
Two recurring issues in design
Performance
Exclusive use of resources
Three basic implementation mechanisms
Processor modes
Kernels
Method of invoking system service

21. Performance
Must be as efficient as possible in use of resources (especially processor and memory)
Every design issue MUST be evaluated wrt its contribution to functionality of system AND its impact on performance
Seek to minimize “overhead” of the system wrt the applications running on the system
Increased hardware performance does allow added functionality in spite of inefficiency

22. Typical Computer at 1980 and 2000

23. Exclusive Use of Resources
Multiprogramming  resource sharing
Therefore, need software-controlled resource isolation
Security policy: Sharing strategy chosen by computer’s owner
Protection mechanism: Tool to implement a family of security policies

24. Exclusive Use of Resources – cont
Security depends on correct operation of software  trusted vs. untrusted software
Need to insure that untrusted software cannot change trusted software
Can limit the function of the OS
Guiding a manned spaceship
Managing a nuclear reactor

25. Processor Modes Mode bit: Supervisor or User mode
Some processors may have more than one mode
Supervisor mode (privileged, protected)
Can execute all machine instructions
Can reference all memory locations
User mode
Can only execute a subset of instructions
Can only reference a subset of memory locations

26. Processor Modes – cont Ensures proper operation of a computer system
Protect the operating system and all other programs and their data from any malfunctioning program
Protection is needed for any shared resource
Trusted OS software runs in supervisor mode
All other software runs in user mode

27. Processor Modes – cont Supervisor mode User mode
all instructions are legal
all addresses are absolute physical addresses (base and bound are not used)
User mode
instructions that modify control registers are illegal
all addresses must be less than bound and have base added to them

28. Privileged Instructions
Instructions that can only be executed in the supervisor mode are called supervisor, privileged, or protected instructions
I/O instructions are privileged instructions
A user program in user mode cannot perform its own I/O
Instruction to change the mode is a privileged instruction
Instruction to set the halt flag is a privileged instruction

29. Exclusive Access to a Resource
Process A
Supervisor
Program
A’s Protected
Object
Processor
Process B
When A is using processor, register points to its object
When B is using processor, register does not point to A’s object

30. Kernels Kernels Extensions to the OS execute in user mode
Critical parts of OS that run in supervisor mode
Have access to other parts of the kernel
Trusted software
Extensions to the OS execute in user mode
The trap instruction is used to switch from user to supervisor mode, entering the OS

31. Trap Instruction S Trusted Code Mode Branch Table User Supervisor 1 23
Trusted
Code
User
Supervisor

32. Trap Instruction – cont.…
fork();
fork() {
trap N_SYS_FORK() }
sys_fork()
sys_fork() {
/* system function */
return;
Kernel
Trap Table

33. Requesting Services from O.S.
Two techniques
System call
Message passing
call(…);
trap
return;

34. How to Make a System Call
For the system
through a trap instruction which causes an interrupt
Hardware saves PC and current status information
Hardware changes mode to system mode
Hardware loads PC from system call interrupt vector location.
Execute the system call interrupt handler
return from the handler, restores PC and other saved status information
User process continues.

35. System Call Flow of Control…
fork();
fork() {
trap N_SYS_FORK() }
sys_fork()
sys_fork() {
/* system function */
return;
Kernel
Trap Table

36. How to Make a System Call – cont.
Parameter passing
Through registers
System call number passed through register
Parameters are passed through registers
Returned value is also passed through a register to C/C++
Through a table in memory
Pass the address of the table in a register
Through the stack
Push the parameters on the stack by the user program
Pop the parameters off the stack by the O.S.

37. A Thread Performing a System Call
User Space
Kernel Space
fork();
sys_fork() { }
Thread

38. Requesting Services – cont.
Two techniques
System call
Message passing
send(…, A, …);
receive(…, B, …);
receive(…A, …); …
send(…, B, …);
send/receive

39. Basic OS Organization Processor(s) Main Memory Devices
Process, Thread &
Resource Manager
Memory
Manager
Device
File

40. Operating System Examples
UNIX
MACH
MS-DOS
Windows NT
OS/2
MacOS

41. UNIX One of the most popular operating systems
First version released in 1969
By Ken Thompson & Dennis Ritchie at Bell Labs
ACM Turing Award – 1983
National Medal of Technology – 1999
Japan Prize for Information and Communications – 2011
Widely used in universities and research organizations
Time-sharing system
Supports multiple processes
Disk files and I/O devices are treated similarly

42. History of UNIX Versions

43. Advantages of UNIX Written in a high-level language.
Distributed in source form.
Provided powerful operating-system primitives on an inexpensive platform.
Small size, modular, clean design.

44. UNIX Design Principles
Designed to be a time-sharing system
Has a simple standard user interface that can be replaced.
File system with multilevel tree-structured directories.
Files are supported by the kernel as unstructured sequences of bytes.
Supports multiple processes; a process can easily create new processes.
High priority given to making system interactive, and providing facilities for program development.

45. OS System Call Interface
UNIX System Structure
Libraries
Commands
Device Driver
Interactive User
Application
Programs
OS System Call Interface
Driver Interface …
Monolithic Kernel Module
Process Management
Memory Management
File Management
Device Mgmt Infrastructure
Trap Table

46. Current Status UNIX is copyrighted – now supported by SCO
long litigious story there!
Open source variations
freebsd
Linux
many distributions

47. Windows NT
32-bit preemptive multitasking operating system for modern microprocessors.
Key goals for the system:
portability
security
POSIX compliance
multiprocessor support
extensibility
international support
compatibility with MS-DOS and MS-Windows applications.
Uses a micro-kernel architecture.
Available in two versions, Windows NT Workstation and Windows NT Server.
In 1996, more NT server licenses were sold than UNIX licenses

48. Windows NT Organization
Processor(s)
Main Memory
Devices
Libraries
Process
Subsystem
User
Hardware Abstraction Layer
NT Kernel
NT Executive
I/O Subsystem T
Process Management
Memory Management
File Management
Device Mgmt Infrastructure

49. History of Windows NT
In 1988, Microsoft decided to develop a “new technology” (NT) portable operating system that supported both the OS/2 and POSIX APIs.
Originally, NT was supposed to use the OS/2 API as its native environment but during development NT was changed to use the Win32 API, reflecting the popularity of Windows 3.0.

50. Windows NT Design Principles
Extensibility — layered architecture.
NT executive, which runs in protected mode, provides the basic system services.
On top of the executive, several server subsystems operate in user mode.
Modular structure allows additional environmental subsystems to be added without affecting the executive.

51. Window NT Design Principles - Cont.
Portability — NT can be moved from one hardware architecture to another with relatively few changes.
Written in C and C++.
Processor-dependent code is isolated in a dynamic link library (DLL) called the “hardware abstraction layer” (HAL).
Reliability — NT uses hardware protection for virtual memory, and software protection mechanisms for operating system resources.

52. Window NT Design Principles - Cont.
Compatibility — applications that follow the IEEE (POSIX) standard can be complied to run on NT without changing the source code.
Performance — NT subsystems can communicate with one another via high-performance message passing.
Preemption of low priority threads enables the system to respond quickly to external events.
Designed for symmetrical multiprocessing.
International support — supports different locales via the national language support (NLS) API.

53. Windows NT Architecture
Layered system of modules.
Protected mode — HAL, kernel, executive.
User mode — collection of subsystems
Environmental subsystems emulate different operating systems.
Protection subsystems provide security functions.