1. Operating Systems: A Modern Perspective, Chapter 3

2. Operating System Organization3
Operating System Organization
Operating Systems: A Modern Perspective, Chapter 3

3. Purpose of an OS Coordinate Use of the Abstractions Processes
Create the Abstractions
Operating Systems: A Modern Perspective, Chapter 3

4. Operating Systems: A Modern Perspective, Chapter 3
OS Requirements
Provide resource abstractions
Process abstraction of CPU/memory use
Address space
Thread abstraction of CPU within address space
Resource abstraction
“Anything a process can request that can block the process if it is unavailable”
NT uses “object abstraction” to reference resources
File abstraction of secondary storage use
Operating Systems: A Modern Perspective, Chapter 3

5. OS Requirements (cont)
Provide resource abstractions
Manage resource sharing
Time/space-multiplexing
Exclusive use of a resource
Isolation
Managed sharing
Operating Systems: A Modern Perspective, Chapter 3

6. Operating Systems: A Modern Perspective, Chapter 3
Abstraction & Sharing
Program
State
Process
Program
State
Process
Libraries
Program
State
Process
OS Services
Abstraction
Manage sharing
ROM Routines
Processor(s)
Main Memory
Devices
Operating Systems: A Modern Perspective, Chapter 3

7. Operating Systems: A Modern Perspective, Chapter 3
OS Design Constraints
Performance
Protection and security
Correctness
Maintainability
Commercial factors
Standards and open systems
Operating Systems: A Modern Perspective, Chapter 3

8. Operating Systems: A Modern Perspective, Chapter 3
Performance
The OS is an overhead function  should not use too much of machine’s resources
Minimum functionality is to implement abstractions
Additional function must be traded off against performance
DOS: one process
UNIX: low level file system
Operating Systems: A Modern Perspective, Chapter 3

9. Operating Systems: A Modern Perspective, Chapter 3
Protection & Security
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
Operating Systems: A Modern Perspective, Chapter 3

10. Correctness & Maintainability
Security depends on correct operation of software  trusted vs untrusted software
Maintainability relates to ability of software to be changed
If either is sufficiently important, can limit the function of the OS
Guiding a manned spaceship
Managing a nuclear reactor
Operating Systems: A Modern Perspective, Chapter 3

11. Operating Systems: A Modern Perspective, Chapter 3
OS Functions
Device management
Process, thread, and resource management
Memory management
File management
Operating Systems: A Modern Perspective, Chapter 3

12. Operating Systems: A Modern Perspective, Chapter 3
Device Management
Device-Independent
Part
Device-Dependent
Part
Device-Dependent
Part
Device-Dependent
Part …
Device
Device
Device
Operating Systems: A Modern Perspective, Chapter 3

13. Process, Thread, and Resource Management
Abstraction
Process
Abstraction
Generic
Resource
Manager
Multiprogramming
Other …
Primary
Memory
Abstract
Resources
Processor
Operating Systems: A Modern Perspective, Chapter 3

14. Operating Systems: A Modern Perspective, Chapter 3
Memory Management
Isolation &
Sharing
Virtual
Memory
Block
Allocation
Process
Manager
Primary
Memory
Storage
Devices
Operating Systems: A Modern Perspective, Chapter 3

15. Exclusive Access to a Resource
Processor
Process A
Process B
A’s Protected
Object
Supervisor
Program
Operating Systems: A Modern Perspective, Chapter 3

16. Operating Systems: A Modern Perspective, Chapter 3
Processor Modes
Mode bit: Supervisor or User mode
Supervisor mode
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
Operating Systems: A Modern Perspective, Chapter 3

17. Operating Systems: A Modern Perspective, Chapter 3
Kernels
The part of the OS critical to correct operation (trusted software)
Executes in supervisor mode
The trap instruction is used to switch from user to supervisor mode, entering the OS
Operating Systems: A Modern Perspective, Chapter 3

18. Supervisor and User Memory
Space
User
Process
Supervisor
Process
Supervisor
Space
Operating Systems: A Modern Perspective, Chapter 3

19. Procedure Call and Message Passing Operating Systems
send(…, A, …);
receive(…, B, …);
receive(…A, …); …
send(…, B, …);
send/receive
call(…);
trap
return;
Operating Systems: A Modern Perspective, Chapter 3

20. System Call Using the trap Instruction…
fork();
Trap Table
Kernel
fork() { …
trap N_SYS_FORK() }
sys_fork()
sys_fork() {
/* system function */ …
return; }
Operating Systems: A Modern Perspective, Chapter 3

21. A Thread Performing a System Call
User Space
Kernel Space
Thread
fork();
sys_fork() { }
Operating Systems: A Modern Perspective, Chapter 3

22. Basic Operating System Organization
File
Manager
Process, Thread &
Resource Manager
Memory
Manager
Device
Manager
Processor(s)
Main Memory
Devices
Operating Systems: A Modern Perspective, Chapter 3

23. The UNIX Architecture … … Interactive User Libraries Commands
Application
Programs …
OS System Call Interface
Trap Table
Device Driver
Monolithic Kernel Module
Process Management
Memory Management
File Management
Device Mgmt Infrastructure
Device Driver …
Driver Interface
Device Driver
Operating Systems: A Modern Perspective, Chapter 3

24. Microkernel Organization
Process
Process
Libraries
Process
User
Supervisor
Server
Server
Server
Device Drivers
Microkernel
Processor(s)
Main Memory
Devices
Operating Systems: A Modern Perspective, Chapter 3

25. Windows NT Organization
Process
Process T T
Process T T T T
Libraries T T T
Process Management
Memory Management
File Management
Device Mgmt Infrastructure
Subsystem
Subsystem
Subsystem
User
Supervisor
I/O Subsystem
NT Executive
NT Kernel
Hardware Abstraction Layer
Processor(s)
Main Memory
Devices
Operating Systems: A Modern Perspective, Chapter 3

26. Monitoring the Kernel Process Process Process Libraries Subsystem
Task
Manager T
Process T T T T
Libraries T T T
pview
pstat
Subsystem
Subsystem
Subsystem
User
Supervisor
I/O Subsystem
NT Executive
NT Kernel
Hardware Abstraction Layer
Processor(s)
Main Memory
Devices
Operating Systems: A Modern Perspective, Chapter 3