• A program that manages the computer hardware.
• Basis for application programs.
• Intermediatary between computer user and hardware.
• Convience vs. Effeciency.

• Hardware, Operating System, Application Programs, and the Users.

• CPU, Memory, and I/O Devices.
• Provides basic computing resources for the system.

• Browsers, word processors, etc
• Defines ways in which hardware is sued to solve users computing problems.
• OS controls proper use of hardware.

• How various hardware and software resources are shared.

• Multiple users access same computer through other terminals.

• Workstation(s) connects to networks of other workstations and servers.
• Dedicated resources, shared resources.

• Another name for Operating System.
• An Operating System is the program most intimately involved with the hardware.
• Operating system decides how to handle requests for resources.

• Manages the execution of user programs to prevent errors and improper use of the computer.
• Concerned with the operation and control of I/O devices.

• One program running at all times on computer.

• Associated with operating system, but not part of kernel.

• All programs not associated with operating of the system.

• Initial Program to run.
• Must know how to load the O.S. and start executing that system.
• Locates and loads into memory the O.S. Kernel.

• Stores Bootstrap.
• ROM or EEPROM.

• Some event signalled by hardware or software.
• Hardware can trigger interrupt at any time.

• Interrupt triggered by software.

• Array of addresses.
• Indexed by a unique device number given with the interrupt request, to provide the address of the interrupt service routine.

• Controls seven or more devices.

• Used to understand device controller and presents uniform interface to the device to the rest of the Operating System.
• Interrupt / Byte

• Used for reducing high overhead produced by buil data movement such as disk I/O.
• Interrupt / Block
• Transfers entire block from buffer to memory without CPU.

Multiporcessor Systems

(Parallel Systems)

• Two or more processors in close communication, sharing bus, and sometimes clock memory, and peripheral devices.

• Increased Throughput
• Economy of Scale
• Increased Reliability

• The ability to continue providing service proportional to the level of surviving hardware.

• Can suffer a failure of any single component and still continue operation.
• Requires a mechanism to allow the failure to be detected, diagnosed, and if possible, corrected.

• Each processor is assigned a specific task.
• A multiple-processor system.

• Each processor performs all tasks within the operating system.  
• All processors are peers; no master-slave relationship between processors.
• A multiple-processor system.

• Multiple processor boards, I/O boards, and networking board are placed in the same chassis.
• Each blade-processor board boots independently and runs its own operating system.
• In essence, these servers consist of multiple independent multiprocessor systems.

• Gather together multiple CPUs to accomplish computational work.
• Differ from multiprocessor systems, however, in that they are composed of two or more individual systems -- or nodes -- joined together.

• Service will continue even if one or more systems in the cluster fail.
• Obtained by adding a level of redundancy in the system.

• One machine is in hot-standby mode while other is running the applications.

• Monitors the active server.  If it fails, then hot-standby host becomes the active server.

• Two or more hosts are running applications and are monitoring each other. 
• Uses all hardware; More efficient.
• Requires that one application be available to run.

• Can supply significantly greater computational power than single-processor or even SMP systems.
• Capable of running an application concurrently on all computers in the cluster.
• Uses parallelization.

• Consists of dividing a program into separate components that run in parallel on individual computers in the cluster.
• Once each computer node in the cluster has solved its portion of the problem, the results from all nodes are combined into a final solution.

• The supply of access control and locking to ensure that no conflicting operations occur.

• Allow many systems to attach to a pool of storage.
• Can assign the application to run on any host that is attached to the SAN.

• Increases CPU utilization by organizing jobs (code and data) so that the CPU always has one to execute.

• Where jobs are kept initially on the disk.
• Consists of all processes residing on disk awaiting allocation of main memory.
• Main memory is too small to accomodate all jobs.

Time sharing

(or Multitasking)

• A logical extension of multiprogramming.  
• The CPU executes multiple jobs by switching among them.
• Switches occur so frequently that the users can interact with each program while it is running.

Interactive Computer System

(hands on)

• Provides direct communication between the user and the system.
• The user gives instruction to the operating system or to a program directly, using a input device such as a keyboard or a mouse, and waits for immediate results on an output devices.
• The response time is kept short.