1. Introduction to Operating Systems Concepts
Chapters 1 and 2
These slides include text, figures, and information from Operating Systems Concepts, by Silberschatz, Galvin, and Gagne. They also include material from the slides that accompany that textbook and from slides made by Dr. Roger deBry.

2. Four components of a computer system
Users
User
User
User
Four components of a computer system
Programs
System and Application Programs
API: Language Libraries and System Calls OS
Operating System Kernel
Hardware
CPU

3. OS as an abstract machine
This program does not need to have information about the particular hardware in the computer system. It sees the computer as an abstract machine.
Executing
Program
Operating System
Details of the actual hardware and devices are hidden.
Hardware
Device
Device
Device

4. OS as a resource manager
This program has no sense of sharing the system’s resources with other programs. It sees an abstract machine that has all of the resources that it needs.
Executing
Program
Resources
Memory
CPU
General purpose registers
Status registers
Stack
Input/Output devices
Execution
Context
Operating System
Hardware
Device
Device
Device

5. Computer system organization
app
app
app
cpu
memory
system bus
. . .
disk
controller
device
controller
device
controller
printer
keyboard

6. Computer system operation
app
app
app
cpu
memory
The CPU and devices
work concurrently.
system bus
Each device controller is in charge of a particular device type.
. . .
disk
controller
device
controller
device
controller
printer
keyboard

7. Interrupts
An interrupt causes control to branch to an interrupt
service routine through an interrupt vector.
The address of the interrupted instruction is saved.
Incoming interrupts are disabled while an interrupt
is being processed.
A trap is a software generated interrupt.
An operating system is interrupt driven.
The operating system saves the state of the CPU (registers, PC), handles the interrupt, and then resumes where it left off.

8. von Neumann architecture

9. I/O Processing Synchronous Asynchronous requesting process
device driver
wait
interrupt handler
hardware
data
requesting process
device driver
interrupt handler
hardware
data

10. I/O Processing Synchronous I/O requesting process
device driver
wait
interrupt handler
hardware
data
1. A process starts an I/O operation
2. The requesting process waits until the I/O completes

11. I/O Processing Asynchronous I/O requesting process
device driver
interrupt handler
hardware
data
1. A process starts an I/O operation.
2. An acknowledgement is returned.
3. The process continues execution.
4. The device interrupts the process when the I/O is complete.

12. Storage-device hierarchy
Speed
Cost
Volatility
Caching
Device drivers

13. Performance of various levels of storage
Silberschatz Figure 1.11

14. Processor Modes
Modern computing hardware provides multiple modes of operation:
User Mode
Cannot execute all machine instructions (e.g. I/O).
Can only access memory allocated to the process.
Privileged Mode
Executes any instruction in the repertoire.
Can access protected memory.
Only executes trusted software (The OS kernel).

15. Dual-mode operation User mode Kernel mode
Protect the OS and other system components
User mode
Kernel mode
System calls
Privileged instructions

16. Process management
Schedules the processor so that each thread/process receives an equitable fraction of the available time, and maintains the execution context for each thread (stack, registers, etc)
Allocates resources to processes when they are requested and keeps track of resources when a thread is finished with them. Isolates access to resources or allows sharing of resources as required.

17. Threads
A thread, or thread of execution, is the set of instructions being executed in a process.
Single-threaded environment
Multi-threaded environment
Each thread has its own runtime stack, registers, and state information, but they all share the same address space in memory (program and data),
and the same files.

18. Memory management
Keeps track of which parts of memory are currently being used and by whom.
Decides which processes (or parts thereof) and data to move into and out of memory.
Allocates and deallocates memory space as needed.
Provides virtual memory (address space larger than physical memory).

19. File Management
Works with the device managers to give applications a logical view of storage (byte stream, indexed data, text files, etc), and manage the flow of information between the actual storage device and the program.

20. Device Management
The OS manages the allocation, isolation, and sharing of devices.
* Terminals
* Disk Drives
* Printers
* Networks
* Keyboard
* etc

21. Device Drivers Device Independent Part
Application Programming Interface
Device Independent Part
Device Driver Interface
Vendor
Specific
Part
Vendor
Specific
Part
Vendor
Specific
Part

22. Operating system services

23. Command interpreter
CLI or command interpreter allows direct command entry
Sometimes implemented in kernel, sometimes by systems program
Sometimes multiple flavors implemented – shells
Primarily fetches a command from user and executes it
Sometimes commands built-in, sometimes just names of programs
If the latter, adding new features doesn’t require shell modification

24. System calls

25. System calls

26. Standard C library example

27. Operating System Structure
Monolithic: MS-DOS, Unix
Layered: iOS
Microkernel: Mach (used in macOS)
Modules: Solaris, Linux

28. Monolithic: MS-DOS

29. Monolithic: Unix

30. Layered
iOS

31. Microkernel: Mach
Move as much as possible from kernel space into user space.
Message passing

32. macOS

33. Modules: Solaris Kernel modules are loaded as needed.
Modules communicate with each other over known interfaces.

34. Structure summary Structure Examples Advantages Disadvantages
Monolithic
Unix, MS-DOS, Windows
Performance
Hard to implement and maintain
Layered
iOS
Modular, easy to implement and debug
Hard to define layers, less efficient
Microkernel
Mach, macOS
Easy to extend, easy to port, more stable
Performance is not as good
Modules
Hybrids that include modules: Linux, Solaris, and Windows
Modular, more flexible

35. System boot Bootstrap loader stored in ROM or
ROM code loads bootstrap loader from boot block
Bootstrap loader loads kernel and starts it running