• Operating systems have evolved with computer systems
• Expensive machines, efficient operating systems
• Simple machines, simple operating systems
  • Single user machine - no OS needed, input-process-output
  • Batch processing - processes multiple jobs, one after another, with minimal delay
  • Interactive Processing - Allow user interaction as program runs
  • Real Time Processing - respond to hardware events
  • Multitasking - allow multiple tasks to execute simultaneously, switches very fast between tasks
  • Multiprocessing - allow tasks to run on different CPUs
• Examples: Windows XP, Windows 2000, Windows 95, DOS, MacOS, UNIX, Linux, VMS, OS/2

• Software
  • Application - Ex: Word,
  • System
    • Utility - Ex: Windows Explorer
    • Operating System
      • Shell - Ex: GUI Interface, command line
      • Kernel - Implementation

Some software seems to fit somewhere between these units.

The OS kernel contains several key components related to software access to hardware.

• Process Management
  • User interaction
  • batch vs. interactive processing
  • which process is running?
  • What can a particular program access?
• Memory Management
  • Where is a program stored in RAM?
  • Virtual memory management
• File System Management
  • How are files stored on the disk?
  • Can anyone access a file?

We can think of the OS as a broker between our programs and the hardware. One job of the OS is to protect our programs from other programs, and likewise limit what our programs can do.

• A process is a program in action, and has a particular state at any given time
• The process state is either
  • running - actively in CPU
  • waiting - waiting for some event to happen
  • ready - waiting for CPU to become available
• In a multitasking system, processes are constantly being shuffled in and out of the CPU (See fig 3.6, p. 133). This is called a context switch and the following occur:
  • running process is sent an interrupt
  • completes current machine instruction
  • saves current process context
  • executes the interrupt handler (via jump instruction)
  • program is put in ready or waiting queue
• A context switch can occur because of
  • Process has completed a time slice (ready queue)
  • Process has performed an I/O operation (waiting queue)

• A client issues requests which are processed and responded to by a server.
• Separates user oriented I/O from server functions.
• What are some client programs?
• What are some server programs?

• An OS is a resource broker (CPU time, memory, device time, disk space, etc)
• How should we allocate these resources to processes?
• What if 2 or more processes want to access the same device?
• Solution:
  • Mutual exclusion (allow only one)
  • test-and-set instruction

• Deadlock is a state where two processes cannont proceed because they are mutually blocking one another.
• Three conditions must be satified for deadlock to occur:
  • Competition for nonsharable resources
  • Resources are requested on a partial basis (not all at once)
  • No removal of resources once allocated
• Deadlock can be avoided by eliminating one of these conditions
• Deadlock can be corrected by detection then removing the allocation of a resource
  
• Dining Philosophers

• A computer network is a communication channel between two or more computers.
• Network types:
  • LAN - Local Area Network
  • Wan - Wide Area Network
  • Internet - Many LANs linked by WANs
• Network communication follows protocols. Examples: HTTP, SMTP, and FTP
• Networks use different physical media. Examples: Copper, Optical Fiber, and Satelite
• Networks use various topologies. Examples: Star, Ring, and Bus

• Internet was developed in the late 1960s
• Started as DARPA project
• Early applications: file sharing, email, and remote access
• Millions of Machines worldwide
• Uses TCP and IP protocols for low level communications
• Addressing: IP addresses are 32 bits, usually specified as 4 bytes (147.124.43.50)
• Dynamic host/domainname (zeta.albion.edu) to IP (147.124.43.50) address translation
• Controlled by InterNIC
• Predates the web browser (as does hypertext)
• A Uniform Resource Locator (URL) specifies a protocol, machine, and target
• Millions of clients, Millions of servers!
• Not 'Invented' by Al Gore, but he did make significant contributions from a legislativce standpoint
• Internet Timeline

• How do we know a message we send is received on the other end? Protocols!
• Layers of internet connectivity
  • Application Layer
  • Transport Layer
  • Network Layer
  • Link Layer
    • Token Ring
    • CSMA/CD (Carrier Sense, Multiple Access, with Collision Detection)

• How can we protect data and allow access?
  • Passwords
  • Encryption
  • Restricted access
• What are some problems?
  • Vandalism
  • Information Theft
  • Spying/Violation of Personal E-Space
  • Junk Email

Social Issues

• see questions on pages 165 and 166.

• Is Microsoft a monopoloy?
• Can we ever transmit a secure message?
• Who, if anyone, should control access to encryption?
• Who, if anyone, should restrict internet access?
• What should the penaly be for producing/spreading a computer virus?
• What rights do businesses have on control of domainnames?
• Should access ever be anonymous?