1. Chapter 1: Introduction

2. Chapter 1: Introduction
What Operating Systems Do
Computer-System Organization
Operating-System Structure
Operating-System Operations
Process Management
Memory Management
Storage Management
Protection and Security

3. Distributed Systems
Real-Time/Embedded Systems

4. Objectives
To provide an overview of the major operating systems components
To review basic computer system organization

5. What is an Operating System?
A program that acts as an intermediary between a user and hardware
Operating system goals:
Execute user programs and make solving user problems easier
Make the computer system convenient to use
Use the computer hardware efficiently

6. Computer System Structure
Computer system can be divided into four components
Hardware – provides basic computing resources
CPU, memory, I/O devices
Operating system
Controls and coordinates use of hardware among various applications and users

7. Application programs
Word processors, compilers, web browsers, database systems, video games
Users/clients
People, machines, other computers

8. Four Components of a Computer System

9. Operating System Definition
OS is a resource allocator
Manages all resources
Decides between conflicting requests for efficient and fair resource use
OS is a control program
Controls execution of programs to prevent errors and improper use of the computer
Kernel: Core of OS

10. Computer Startup bootstrap program is loaded at power-up or reboot
Firmware stored in ROM or EPROM
Initializates the system
Loads operating system kernel and starts execution

11. Computer System Organization
CPU(s) & device controllers connect through common bus providing access to main memory

12. Storage-Device Hierarchy
Faster
More Expensive

13. Caching Data temporally copied from slower to faster storage
Check cache first
Cache < Storage being cached
How to determine appropriate cache size
Replacement policy
Cache coherency in multiprocessor environment

14. SRAM Stores a bit in a flip-flop Two cross connected NAND or NOR gates
Stores a bit as long as power is applied
Consumes less power than DRAM but more complex circuitry
Generally requires 6 transistors
More expensive

15. DRAM One transistor + Capacitor
Electrical charge on capacitor leaks over time
Periodically refresh
Slower than SRAM
Consumes more power
Cheaper than SRAM
Simpler circuitry

16. Operating System Structure
Multiprogramming
Efficient resource usage
Single user cannot keep CPU and I/O devices busy at all times
Organizes jobs so that CPU always has one to execute
A subset of total jobs in system is kept in memory
When a job blocks, e.g., for I/O, OS switches to another job

17. CPU switches jobs very frequently
Timesharing/Multitasking
CPU switches jobs very frequently
Users can interact with each job while it is running, creating interactive computing
Response time should be < 1 second
Each user has at least one program executing in memory process
If several jobs ready to run at the same time  CPU scheduling
If processes don’t fit in memory, swapping moves them in and out to run
Virtual memory allows execution of processes not completely in memory

18. Memory Layout for Multiprogrammed System

19. Operating System Operations
Hardware Interrupts
Software error or request creates exception or trap
Division by zero
Other problems: infinite loop, processes modifying each other or OS
Accounting & resource management
Protection

20. Basic Protection Dual-mode operation User mode & kernel mode Mode bit
Distinguish whether system is running user code or kernel code
Privileged instructions only executable in kernel mode
System call
Change to kernel mode
Process the system call
Return the result
Switch back to user mode

21. Process Management Unit of work Single- or multi-threaded
A process is a program in execution
Unit of work
Single- or multi-threaded
Resource allocation
Process needs resources to accomplish its task
CPU, memory, I/O, files, data
Resources reclamation at process termination
Program counter indicates the location
Multiple processes can run concurrently on one or more CPUs
Concurrency by multiplexing the CPUs among the processes / threads

22. Process Management Activities
Create and delete both user and system processes
Suspend and resume processes
Provide mechanisms for process synchronization
Provide mechanisms for process communication
Provide mechanisms for deadlock handling

23. Memory Management
Instruction and data need to be in main memory to be processed
Keep track of which parts of memory are currently used and by whom
Decide which processes and data to move into and out of memory
Allocate and deallocate memory space as needed

24. Mass Storage Management
Performance bottleneck
Orders of magnitude performance difference between main memory & secondary storage
OS activities
Free space management
Storage allocation
Disk scheduling
Some storage need not be fast
Tertiary storage includes optical storage, magnetic tape
Still must be managed
Varies between WORM (write-once, read-many-times) and RW (read-write)

25. I/O Subsystem Put data in a designated buffer
Hide peculiarities of hardware devices from the user
I/O subsystem responsible for
Buffering: store data temporarily while it is being transferred
Caching: store parts of data in faster storage
Spooling (Simultaneous Peripheral Operations On-Line)
Put data in a designated buffer
I/O device can pull the data at its own rate
Print spooling can let a user do something else while printing and request several prints without waiting for one print request to finish
Device-driver interfaces

26. Two I/O Methods Synchronous Asynchronous Synchronous I/O
Application is blocked until the I/O finishes
Only one I/O device is active
Easy to determine which device needs service
No concurrent I/O possible

27. I/O Interrupts Extract interrupt service vector
Look up interrupt service table
Save the current process status such as the register values and address of the interrupted instruction
Disable interrupt if necessary
Transfer control to the interrupt service routine

28. Interrupt Timeline

29. Direct Memory Access Structure
Used for high-speed I/O devices able to transmit information at close to memory speed
Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention
Only one interrupt is generated per block, rather than one interrupt per byte
Cycle stealing

30. Device-Status Table

31. Computer system architecture
Single processor systems
Multiprocessor systems
Multiple CPUs sharing main memory
Objectives
Increase throughput
Fault tolerance
Asymmetric multiprocessing
A master processor controls the system
Symmetric multiprocessing (SMP)
All processors are peers
No master-slave relation

32. Multiprocessor systems (continued)
Multicore CPU
Essentially multiprocessors on a single chip
Faster communications between processors
Uses much less power than multiple single-core chips
Good for servers such as web/database servers

33. Clustered systems Distributed systems
A cluster consists of two or more individual systems unlike multiprocessor systems
Clustered computers share storage and linked by a local area network, e.g., Ethernet or InfiniBand
To support fault tolerance and high performance, for example, in a web server farm
Distributed systems

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