Overview  This and the other PowerPoint files represent an outline only. Each student is responsible for additional details specified in the book or in class

 The web site [ has a collection of practice problems and solutions. At the end of each chapter, you should download the exercises, write the solutions and then check them against the published solutions.

Chapter 1:  What is an OS? Coordinate access to resources Make hardware usable Allocate resources Schedule activities Control flow of information among hardware components. Traffic cop

 What actually constitutes an OS is not that simple (see author’s comments on the second paragraph on page 6)

 Overview of a computer system: Fig 1.2  Machine Language instruction format (von Neumann architecture). Fetch-analyze-execute cycle.  Fetch an instruction and store in the Instruction register  Analyze it  Execute it, if possible Registers: general, program counter, instruction register.

 Storage hierarchy: fig 1.4

 Types of environments Batch Time-sharing Interactive Real-Time Single-processor Multiprocessor

 Multiprocessor Asymmetric (master-slave model) Symmetric (processors are peers) – most common Clustered – like multiprocessor except consists of 2 or more entire systems coupled together. Clustered may mean different things to different people.

 Types of OS Single tasking Multitasking (sometimes called timesharing) Multiuser

 Interrupts vs. traps (exceptions). Interrupt: Occurrence of an event that requires that the CPU be interrupted from what it is doing in order to execute an interrupt handling routine (e.g. completion of an I/O or a hardware failure) Trap: an event typically caused by the CPU such as an attempt to divide by 0, numeric overflow, or illegal memory reference. Requires execution of a trap-handling routine.

 Dual modes (user mode; monitor, kernel, or supervisor mode) – defined by an internal CPU bit; privileged instructions.  Process: an entity capable of requesting and using computer resources. E.g. a program in execution.

OS responsibilities  Process management: Creating/deleting processes. Process synchronization. Interprocess Communication. Suspending/resuming processes. Deadlock handling:

 Memory management:  Allocation/deallocation of memory  What processes go into memory and where  What part of memory is occupied/available.  Static/dynamic allocation

 Caching (paging, hardware caching).  Security: protect memory from other processes.

 Scheduling Which processes run? For how long? Which have higher priority? Are they waiting for something?

 File management: Create/delete files Maintain directories Storing files on secondary storage File access File security Manage disk space (auxiliary storeage management)

 Goals Consistency Scalability Ease of use Efficiency Throughput Responsiveness

 Above goals are often contradictory. Ease of use often implies guis which are NOT efficient. Linux is known to be stable and efficient, but not easy to use.  Best throughput may be obtained by ignoring certain activities, which means bad response times for them.

 Examples DOS Various windows flavors Various Unix flavors VMS MVS Mac

 Distributed systems: collection of processors, each with its own local memory, connected by high-speed lines.  Embedded systems: Most common – embedded in consumer devices (cars, DVDs, robotic arms, cell phones, ipods, etc)

 Client-server computing  Peer-to-peer computing.  Can skip this stuff.

Chapter 2:  Shell/command interpreter. Commands are really files (e.g. ls, rm, cat, etc.)  Interface: command line or gui.  Linux flavors have various shells: Bourne shell, C shell, Korn shell. They look alike but there are small differences.  We use the 2 nd version of the Bourne shell. It’s called bash (Bourne Again Shell).

 System Calls: interface to service made available by the OS API (Application programmer interface): set of functions available to the programmer. Examples: fopen, read, write, close, fork, wait, exec, etc. Linux command handout has those we will use in this class.

Types of calls: fig 2.5 Can skip most of the stuff on system calls – not needed for this stage of the course

OS structure  Simple structure: eg - DOS allowed programs to access routines that write directly to display and drives. Vulnerable to crashes. Fig 2.10  Kernel: most critical components; like to keep resident in memory  Layered design: Fig 2.11 and 2.12  Basic design principle to insulate the needs of a layer from the details of the next lowest layer

Microkernel:  As systems evolved, kernels grew larger.  Removes all nonessential components from the kernel and implements as system or user level programs.  Not always consensus on everything kernel should contain.

 Linux and Mac OS use a modular kernel. See example in Fig  Windows XP is a layered system of modules (Figure 22.1)

Virtual machine:  Abstraction of hardware components.  Illusion of having your own machine.  Can be useful for testing OS changes/enhancements.  More secure (each application runs on it's own "machine")  IBM's VM operating system.  Server virtualization.

Java – more than just a language  Language spec - the stuff you learned  API – support for graphics, I/O, database connectivity, networking, server apps, support for telephones, pagers, etc.  Virtual machine spec. Java Virtual Machine (JVM) – Fig 2.17