1. Intro and System Overview
Operating Systems
Intro and System Overview
Operating Systems: Internals and Design Principles, 8th ed., Stallings
Modern Operating Systems, 5th ed., Tanenbaum and Bos

2. Intro
Intros
Course Policy
Syllabus, Textbook
Learning Objectives

3. Outline OS Evolution Modern OS Developments System Components
The Execution Cycle
Interrupts
The Memory Hierarchy
Input and Output
Multiprocessors

4. Learning Objectives Describe the key functions of an OS
Discuss the evolution of operating systems, and explain each major achievement
Define and discuss virtual machines
Explain OS design issues raised by multiprocessing

5. Learning Objectives
Name and describe the function of common components in a computer system
Describe the typical CPU instruction cycle
Explain the operation of CPU interrupts
Describe the memory hierarchy, and how its various elements interact
Explain the difference between programmed I/O, interrupt-driven I/O, and DMA
Understand multiprocessor architecture differences

6. OS Evolution

7. Operating System
A program that controls the execution of application programs
An interface between applications and hardware
Main objectives of an OS
Convenience
Efficiency
Adaptability
(image: XKCD)

8. Operating System Services
Program development
Program execution
Access to I/O devices
Controlled access to files
System access
Error detection and response
Accounting
A computer is a set of resources for the movement, storage, and processing of data
The OS is responsible for managing these resources.
(image: XKCD)

9. Evolution of Operating Systems
Serial processing
No OS: programmers work directly with hardware
Users have access to the computer in “series”
Lots of setup time required
Simple batch systems
Multiprogrammed batch systems
Time-sharing systems

10. Simple Batch Systems Monitor: program that switches jobs
User no longer has direct access to the processor
Monitor is always in memory
Operator batches jobs together and places them on an input device
Each program branches back to the monitor when finished
Monitor runs in kernel mode, user jobs run in user mode
Example: IBM 701 (~1953)
IBM 701 (image: IBM)

11. Batch Multiprogramming
Memory is expanded to hold multiple programs
Programs, or "jobs," are not interactive with terminal/user
Controller switches between them without waiting for program completion
Example: UNIVAC 1107 / EXEC II (~1962)
UNIVAC 1107 (image: fourmilab.ch)

12. Time-Sharing Systems Can be used to handle multiple interactive jobs
Processor time is shared among multiple users
Multiple users simultaneously access system terminals
OS interleaves the execution of each user program in a short burst, or quantum, of computation
Example: CTSS / IBM7094 (mid-late 1960s)
Comparison of Multiprogramming Systems
IBM (image: IBM)

13. Modern OS Developments

14. Process Fundamental to the structure of operating systems
A process can be defined as:
A program in execution
An instance of a running program
The entity that can be assigned to, and executed on, a processor
A unit of activity characterized by at least one sequential thread of execution, a current state, and an associated set of system resources

15. Components of a Process
A process contains three components:
An executable program
The associated data needed by the program
The execution context of the program
Execution Context
Internal data the OS uses to supervise and control a process
Register contents
Process priority
Status: run, suspend, blocked, etc.

16. Modern OS Developments
Monolithic Kernel
Common until ~1990s
Single process for everything - scheduling, file system, device drivers, memory management, etc.
Single shared address space
Microkernel
Kernel has only the most essential functions: scheduling, address space, IPC, etc.
All other OS services implemented separately, called as needed
Microkernel Advantages
Flexibility
Fault tolerance
Speed
Simpler implementation

17. Microkernels
Most OS services run as modules that the kernel can load as needed
The kernel contains only the most vital OS components
Simplified structure of the MINIX 3 system

18. Modern OS Developments
Multithreading: a process is divided into threads, which may run concurrently
Process: a collection of one or more threads, and associated system resources
Thread: a dispatchable unit of work, which includes the process' context
Symmetric Multiprocessing (SMP)
OS may take advantage of SMP by scheduling threads appropriately

19. Modern OS Developments
Distributed operating system
Provides the illusion of:
A single main memory space
A single secondary memory space
Unified file system and other features
Object oriented design
Improves OS extensibility, eases development
Examples: .NET framework, Objective-C/Cocoa

20. Virtualization
Enables a single PC or server to simultaneously run multiple OS's or sessions of an OS
A machine can host numerous applications, including those for a different OS, on one platform
Host OS can support a number of VMs

21. Type I VMM - sees hardware state
Virtualization
Type I - VMM/Hypervisor runs on hardware
Examples: VMware ESX, Xen
Type II - VMM/Hypervisor is 'hosted'
Examples: VMware Workstation, Parallels, VirtualBox
Hardware
Type II VMM
Guest OS #1 #2
Apps for
OS #1
OS #2
Apps for Host OS
Host Operating System
Hardware
Type I VMM - sees hardware state
Guest OS #1 #2 #3
Apps for
OS #1
OS #2
Apps for OS #3

22. OS Design for Multiprocessing
Concurrent processes or threads
Re-entrant kernel routines, etc.
Scheduling
Synchronization
Mutual exclusion and event ordering
Memory management
Reliability
Graceful degradation if a processor fails
(image: yogamammaexhales.blogspot.com)

24. Computer System Overview

25. Operating System Functions
Employs hardware resources of one or more processors
Provides a set of services to system users
Manages secondary memory and I/O devices

26. Key Interfaces Instruction set architecture (ISA)
Components: registers, flags, timers, interrupts, etc.
Machine code instruction definitions
Examples: IA64, x86, MIPS, SPARC
Application binary interface (ABI)
Conventions: e.g. 2's complement, big endian, etc.
How functions are called and arguments are passed
How the OS should manage syscalls
Format of binary executable files
Application programming interface (API)
Exported to applications by the OS

27. Computer System Elements
Processor (or CPU)
Controls system operation
Main Memory
Volatile, stores data and programs
Also called "real memory" or "primary memory"
I/O Modules
Move data between computer and external environment, such as hard disk, display, keyboard, etc.
System Bus
Facilitates communication among processors, main memory, and I/O modules

28. Special-Purpose Processors
GPUs - graphical processing units
Efficient computation on arrays using Single-Instruction Multiple Data (SIMD)
Numeric processing, physics simulations, games, large spreadsheet computation
Parallel computing standards: CUDA, OpenCL
DSPs - digital signal processors
Streaming audio or video ('codecs'), encryption
Radeon HD 7970M (image: diit.cz)
28nm, OpenGL, DirectX, 2.2 TFLOPS, 75W
(image: ti.fleishman.de)

29. Special-Purpose Processors
SoC - system on chip
Components like DSP, GPU, main memory, cache, and I/O controllers can all go onto a single chip (or "die")
May include analog and mixed-signal components
Often used in embedded applications
A8X SoC for iPad Air 2:
Tri-core ARM v8 CPU
Eight-core PowerVR GPU
(image: anandtech.com)

30. CPU and Execution

31. CPU Components Registers Program Status Word (PSW) Execution Pipeline
General Purpose (x86: $EAX, $EBX, $ECX, $EDX)
Base Pointer ($EBP in x86)
Instruction Pointer ($EIP in x86)
May be called Program Counter
Stack Pointer ($ESP in x86)
Program Status Word (PSW)
Conditions, flags, etc.
Set by instructions, comparisons, CPU mode, etc.
Execution Pipeline

32. Execution Pipeline
Simple Processor
Superscalar
Execution

33. Memory

34. Memory Going down the hierarchy: Decreasing cost per bit
Increasing capacity
Increasing access time
Decreasing frequency of access by the processor

35. Memory Levels CPU Registers Cache Internal Memory Secondary Storage
Access in as little as 1 clock cycle
Cache
Invisible to the OS
Exploits the principle of locality
Internal Memory
Usually volatile
Secondary Storage
Usually external, non-volatile
Used for programs and files

36. Cache Principles Contains a copy of a portion of main memory
Processor first checks cache
If not found, a block of memory is read into the cache
single-level cache
multi-level cache

37. Memory
(a) A quad-core chip with a shared L2 cache (b) A quad-core chip with separate L2 caches

38. Memory Performance 5:1 106:1 Main Memory Cache (RAM vs. Cache)
Virtual Memory
(Paging)
(Disk vs. RAM)
Disk Cache
(Disk swapfile)
Typical Access Time Ratios
5:1
106:1
Management System
Hardware
Hardware and Software
Software
Typical Block Size
4-128 bytes
bytes
Processor Access
Direct
Indirect

39. Locality Spatial Locality Temporal Locality
Tendency of execution to involve a number of memory locations that are clustered
Temporal Locality
Tendency for a processor to access memory locations that have been used recently

40. Input and Output

41. Programmed I/O
The I/O module performs the requested action then sets the appropriate bits in the I/O status register
The processor polls the I/O module status
System performance is severely degraded

42. Interrupt-Driven I/O
Processor issues an I/O command to a module, then goes on to do some other useful work
I/O module interrupts processor when it has acquired the data in a buffer
Processor transfers the data from buffer to memory
More efficient than Programmed I/O, but still requires the processor to transfer the data

43. Direct Memory Access (DMA)
Performed by a separate module on the system bus
Transfers the entire block of data directly to and from memory without going through the processor
More efficient than interrupt-driven or programmed I/O
Processor issues a command to the DMA module containing:
Read or write
I/O device address
Starting address in memory
Number of words to be read/written

44. Intel x86 System Structure Example
Buses
Intel x86 System Structure Example

45. Multiprocessor Architectures

46. Multiprocessing SMP - Symmetric multiprocessors Advantages
Two or more similar processors of comparable capability
All processors can perform the same functions
Interconnected, share main memory and I/O
Advantages
Performance
Scalability
Fault tolerance

47. Multiprocessing Multicore
Two or more processors (cores) on a single die
Each core has execution unit, registers, local cache
Core may employ multiple threads
Intel Core-i7 990X

49. Multiprocessing Challenges Workload balance (scheduling)
Fault redundancy
Scalability of intercommunications (bus traffic)
Coherency of distributed operations
Cache coherency
Instruction ordering

50. Summary OS Evolution Modern OS Developments System Components
The Execution Cycle
Interrupts
The Memory Hierarchy
Input and Output
Multiprocessors