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					                            OPERATING SYSTEMS

 CPU:The CPU is the brains of the computer. Sometimes referred to simply as the
  processor or central processor, the CPU is where most calculations take place.
 Registers:A, special, high-speed storage area within the CPU. All data must be
  represented in a register before it can be processed. For example, if two numbers
  are to be multiplied, both numbers must be in registers, and the result is also
  placed in a register. (The register can contain the address of a memory location
  where data is stored rather than the actual data itself.)

   There are several classes of registers according to the content:

       o Data registers are used to store integer numbers (see also Floating Point
         Registers, below). In some older and simple current CPUs, a special data
         register is the accumulator, used implicitly for many operations.
       o Address registers hold memory addresses and are used to access
         memory. In some CPUs, a special address register is an index register,
         although often these hold numbers used to modify addresses rather than
         holding addresses.
       o Conditional registers hold truth values often used to determine whether
         some instruction should or should not be executed.
       o General purpose registers (GPRs) can store both data and addresses, i.e.,
         they are combined Data/Address registers.
       o Floating point registers (FPRs) are used to store floating point numbers
         in many architectures.
       o Constant registers hold read-only values (e.g., zero, one, pi, ...).
       o Vector registers hold data for vector processing done by SIMD
         instructions (Single Instruction, Multiple Data).
       o Special purpose registers hold program state; they usually include the
         program counter (aka instruction pointer), stack pointer, and status register
         (aka processor status word).

          Instruction registers store the instruction currently being executed.
          Index registers are used for modifying operand addresses during the run
           of a program.

 In some architectures, model-specific registers (also called machine-specific
  registers) store data and settings related to the processor itself. Because their
  meanings are attached to the design of a specific processor, they cannot be
  expected to remain standard between processor generations.
 Registers related to fetching information from random access memory, a
  collection of storage registers located on separate chips from the CPU (unlike
  most of the above, these are generally not architectural registers):
      o Memory buffer register
      o Memory data register
      o Memory address register
      o Memory Type Range Registers
 ALU:The arithmetic logic unit (ALU) is a digital circuit that calculates an
  arithmetic operation (like an addition, subtraction, etc.) and logic operations (like
  an Exclusive Or) between two numbers. The ALU is a fundamental building
  block of the central processing unit of a computer.
 Control Unit:A control unit is the part of a CPU or other device that directs its
  operation. The outputs of the unit control the activity of the rest of the device. A
  control unit can be thought of as a finite state machine.
 Application Program:An application program (sometimes shortened to
  application) is any program designed to perform a specific function directly for
  the user or, in some cases, for another application program. Examples of
  application programs include word processors; database programs; Web browsers;
  development tools; drawing, paint, and image editing programs; and
  communication programs.
 System Software: System software is a generic term referring to any computer
  software which manages and controls the hardware so that application software
    can perform a task. It is an essential part of the computer system. An operating
    system is an obvious example, while an OpenGL or database library are less
    obvious examples. System software contrasts with application software, which are
    programs that help the end-user to perform specific, productive tasks, such as
    word processing or image manipulation.If system software is stored on non-
    volatile storage such as integrated circuits, it is usually termed firmware.
   First Generation Computers: In first generation computers, the operating
    instructions or programs were specifically built for the task for which computer
    was manufactured. The Machine language was the only way to tell these
    machines to perform the operations. There was great difficulty to program these
    computers ,and more when there were some malfunctions. First Generation
    computers used Vacuum tubes and magnetic drums(for data storage).
   Second Generation Computers: In Second Generation computers, the
    instructions(program) could be stored inside the computer's memory. High-level
    languages such as COBOL (Common Business-Oriented Language) and
    FORTRAN (Formula Translator) were used, and they are still used for some
    applications nowdays.
   Third Generation Computers: Although transistors were great deal of
    improvement over the vacuum tubes, they generated heat and damaged the
    sensitive areas of the computer. The Intergreated Circuit(IC) was invented in 1958
    by Jack Kilby. It combined electronic components onto a small silicon disc, made
    from quartz. More advancement made possible the fitings of even more
    components on a small chip or a semi conductor. Also in third generation
    computers, the operating systems allowed the machines to run many different
    applications. These applications were monitored and coordinated by the
    computer's memory.
   Fourth Generation Computers: Fourth Generation computers are the modern
    day computers. The Size started to go down with the improvement in the
    integerated circuits. Very Large Scale(VLSI) and Ultra Large scale(ULSI)
    ensured that millions of components could be fit into a small chip. It reduced the
    size and price of the computers at the same time increasing power, efficiency and
    reliability.
   Fifth Generation Computers: The Fifth Generation Computer Systems
    project (FGCS) was an initiative by Japan's Ministry of International Trade and
    Industry, begun in 1982, to create a "fifth generation computer" (see history of
    computing hardware) which was supposed to perform much calculation utilizing
    massive parallelism. It was to be the end result of a massive government/industry
    research project in Japan during the 1980s. It aimed to create an "epoch-making
    computer" with supercomputer-like performance and usable artificial intelligence
    capabilities.
   POST: Power-on self-test (POST) is the common term for a computer's, router's
    or printer's pre-boot sequence. The same basic sequence is present on all
    computer architectures. It is the first step of the more general process called initial
    program load (IPL), booting, or bootstrapping.
   BIOS: BIOS (basic input/output system) is the program a personal computer's
    microprocessor uses to get the computer system started after you turn it on. It also
    manages data flow between the computer's operating system and attached devices
    such as the hard disk, video adapter, keyboard, mouse, and printer.
   BOOTSTRAP Program: This appendix describes the Bootstrap Program, also
    known as the ROM Monitor. The Bootstrap Program can help you isolate or rule
    out hardware problems encountered when installing your router. A summary of
    the bootstrap diagnostic tests and command options is provided.
   Super Computer: A supercomputer is a computer that leads the world in terms
    of processing capacity, particularly speed of calculation, at the time of its
    introduction. The term "Super Computing" was first used by New York World
    newspaper in 1920 to refer to large custom-built tabulators IBM made for
    Columbia University.
   Mainframe Computer: Mainframes (often colloquially referred to as Big Iron)
    are computers used mainly by large organizations for critical applications,
    typically bulk data processing such as census, industry/consumer statistics, ERP,
    and financial transaction processing.
 Workstation: A workstation, such as a Unix workstation, RISC workstation or
  engineering workstation, is a high-end desktop or deskside microcomputer
  designed for technical applications. Workstations are intended primarily to be
  used by one person at a time, although they can usually also be accessed remotely
  by other users when necessary.
 Workstations usually offer higher performance than is normally seen on a
  personal computer, especially with respect to graphics, processing power,
  memory capacity and multitasking ability.
 Hardware: There are several differences between computer hardware
  and software. However, the fundamental difference between hardware
  and software is that hardware is a physical device something that you're
  able to touch and see. For example, the computer monitor you're
  viewing this text on or the mouse you're using to navigate is considered
  computer hardware.
 Software: Software is code and instructions that tell a computer and/or
  hardware how to operate. This code can be viewed and executed using a
  computer or other hardware device. However, without any hardware
  software would not exist. An examples of software is Microsoft Windows,
  an operating system that allows you to control your computer and other
  programs that run on it. Another example of software is the Internet
  browser you're using to view this page.
 Neumann Architecture of a Computer:The von Neumann architecture is a
  computer design model that uses a single storage structure to hold both
  instructions and data. The term describes such a computer, which implements a
  Universal Turing machine, and the common "referential model" of specifying
  sequential architectures, in contrast with parallel architectures.The separation of
  storage from the processing unit is implicit in the von Neumann architecture. The
  term "stored-program computer" is generally used to mean a computer of this
  design.
 Program Counter: The program counter (also called the instruction pointer,
  part of the instruction sequencer in some computers) is a register in a computer
  processor which indicates where the computer is in its instruction sequence.
  Depending on the details of the particular machine, it holds either the address of
  the instruction being executed, or the address of the next instruction to be
  executed. The program counter is automatically incremented for each instruction
  cycle so that instructions are normally retrieved sequentially from memory.
  Certain instructions, such as branches and subroutine calls and returns, interrupt
  the sequence by placing a new value in the program counter.
 Instruction Register: In computing, an instruction register is the part of a
  CPU's control unit that stores the instruction currently being executed. In simple
  processors each instruction to be executed is loaded into the instruction register
  which holds it while it is decoded, prepared and ultimately executed, which can
  take several steps.
 Non-Volatile memory: non-volatile storage, is computer memory that can retain
  the stored information even when not powered. Examples of non-volatile memory
  include read-only memory, flash memory, most types of magnetic computer
  storage devices (e.g. hard disks, floppy disk drives, and magnetic tape), optical
  disc drives, and early computer storage methods such as paper tape and punch
  cards.
 Non-volatile memory is typically used for the task of secondary storage, or long-
  term persistent storage. The most widely used form of primary storage today is a
  volatile form of random access memory (RAM), meaning that when the computer
  is shut down, anything contained in RAM is lost. Unfortunately, most forms of
  non-volatile memory have limitations that make them unsuitable for use as
  primary storage. Typically, non-volatile memory either costs more or performs
  worse than volatile random access memory.
 Volatile Memory: Volatile memory, also known as volatile storage, is
  computer memory that requires power to maintain the stored information, unlike
  non-volatile memory which does not require a maintained power supply.Most
  forms of modern random access memory are volatile storage, including dynamic
  random access memory and static random access memory. Content addressable
    memory and dual-ported RAM are usually implemented using volatile storage.
    Early volatile storage technologies include delay line memory and Williams tube.
   Random Access Memory: Random Access Memory (usually known by its
    acronym, RAM) is a type of data storage used in computers. It takes the form of
    integrated circuits that allow the stored data to be accessed in any order — that is,
    at random and without the physical movement of the storage medium or a
    physical reading head.
   Read Only Memory: Read-only memory (often referred to as its acronym
    ROM) is a class of storage media used in computers and other electronic devices.
    Because it cannot (easily) be written to, its main uses lie in the distribution of
    firmware (software that is very closely related to hardware, and not likely to need
    frequent upgrading).
   BUS: In computer architecture, a bus is a subsystem that transfers data or power
    between computer components inside a computer or between computers and
    typically is controlled by device driver software. Unlike a point-to-point
    connection, a bus can logically connect several peripherals over the same set of
    wires. Each bus defines its set of connectors to physically plug devices, cards or
    cables together.
   SCSI Controller: Short for small computer system interface, a parallel interface
  standard used by Apple Macintosh computers, PCs, and many UNIX systems for
  attaching peripheral devices to computers. Nearly all Apple Macintosh computers,
  excluding only the earliest Macs and the recent iMac, come with a SCSI port for
  attaching devices such as disk drives and printers.
 SCSI interfaces provide for faster data transmission rates (up to 80 megabytes per
  second) than standard serial and parallel ports. In addition, you can attach many devices
  to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.
 Diff between RAM & ROM: As the name implies, you cannot write to read-only
  memory; your system can only read it during normal operation. The computer
  manufacturer preprograms the data; the data will remain intact without any power.
  Random-access memory allows the CPU to read and write information at any
  time. This information is erased, however, when you turn the system's power off.
  We can further differentiate RAM chips between Static RAM (SRAM) and
  Dynamic (RAM) (DRAM), depending upon whether the data in the cells needs to
  be refreshed. (SRAM doesn't need to be refreshed.)
 Primary Memory: Primary storage, or internal memory, is computer memory
  that is accessible to the central processing unit of a computer without the use of
  computer's input/output channels. Primary storage is used to store data that is
  likely to be in active use. Primary storage is typically very fast, as in the case of
  RAM.
 Secondary Memory:

 Secondary memory (or secondary storage) is the slowest and cheapest form of memory.         
  It cannot be processed directly by the CPU. It must first be copied into primary storage
  (also known as RAM ).
 Secondary memory devices include magnetic disks like hard drives and floppy disks ;
  optical disks such as CDs and CDROMs ; and magnetic tapes, which were the first forms
  of secondary memory.
 Cache Memory: Cache memory is random access memory (RAM) that a
  computer microprocessor can access more quickly than it can access regular
  RAM. As the microprocessor processes data, it looks first in the cache memory
  and if it finds the data there (from a previous reading of data), it does not have to
  do the more time-consuming reading of data from larger memory.
 Hit Ratio in the context of cache memory:The chief measurement of a
  cache, which is the percentage of all accesses that are satisfied by the
  data in the cache. Also known as "hit ratio."
 Compiler: A compiler is a computer program (or set of programs) that
    translates text written in a computer language (the source language) into another
    computer language (the target language). The original sequence is usually called
    the source code and the output called object code.
 Translator:Which translates a source code to an object code.
 Assembler: a computer program to translate between lower-level
    representations of computer programs
 Interpreter: a program designed to run other non-executable programs
   directly.
 Virtual Machine: a virtual machine is software that creates a virtualized
  environment between the computer platform and its operating system, so that the
  end user can operate software on an abstract machine.
 Loader: In computing, a loader is a program that performs the functions of a
  linker program and then immediately schedules the resulting executable program
  for action (in the form of a memory image), without necessarily saving the
  program as an executable file.
 Linker: a linker or link editor is a program that takes one or more objects
  generated by compilers and assembles them into a single executable program.
 Boot Block: An area of a disk having information for loading the operating
  system that is needed to start a computer.
 Binary Code: Computers use the binary system to work with data. All data in the
   computer is stored in binary code as 1's and 0's (bits).
 Object code: The source code consists of instructions in a particular language,
  like C or FORTRAN. Computers, however, can only execute instructions written in
  a low-level language called machine language. To get from source code to machine
  language, the programs must be transformed by a compiler. The compiler produces
  an intermediary form called object code. Object code is often the same as or
  similar to a computer's machine language.

 Dynamic Linking: Dynamic linking defers much of the linking process until a
  program starts running. It provides a variety of benefits that are hard to get
  otherwise:
 Dynamically linked shared libraries are easier to create than static linked shared
  libraries.
 Dynamically linked shared libraries are easier to update than static linked shared
  libraries.
 The semantics of dynamically linked shared libraries can be much closer to those
  of unshared libraries.
 Dynamic linking permits a program to load and unload routines at runtine, a
  facility that can otherwise be very difficult to provide.
 There are a few disadvantages, of course. The runtime performance costs of
  dynamic linking are substantial compared to those of static linking, since a large
  part of the linking process has to be redone every time a program runs. Every
  dynamically linked symbol used in a program has to be looked up in a symbol
  table and resolved. (Windows DLLs mitigate this cost somewhat, as we describe
  below.) Dynamic libraries are also larger than static libraries, since the dynamic
  ones have to include symbol tables.
 Operating Systems: An operating system (OS) is a set of computer
  programs that manage the hardware and software resources of a computer.
 Batch Processing: Batch processing is the execution of a series of programs
  ("jobs") on a computer without human interaction, when possible.
 Interactive Computing: interactive computing refers to software which
  accepts input from humans — for example, data or commands. Interactive
  software includes most popular programs, such as word processors or spreadsheet
  applications.
 Time Sharing: Time-sharing refers to sharing a computing resource among
  many users by multitasking.
 Multiprogramming: Multiprogramming is a rudimentary form of parallel
  processing in which several programs are run at the same time on a uniprocessor.
 Multiprocessing: Multiprocessing is a generic term for the use of two or
  more central processing units (CPUs) within a single computer system.
 Parallel Processing: Parallel processing is the ability of the brain to
  simultaneously process incoming stimuli. This becomes most important in vision,
  as the brain divides and conquers what it sees. It breaks up a scene into four
  components: color, motion, form, and depth. These are individually analysed and
  then compared to stored memories, which helps the brain identify what you are
  viewing. The brain then combines all of these into one image that you see and
  comprehend. This is a continual and seamless operation.
 Interrupt: an interrupt is an asynchronous signal from hardware indicating the
    need for attention or a synchronous event in software indicating the need for a
    change in execution. A hardware interrupt causes the processor to save its state of
    execution via a context switch, and begin execution of an interrupt handler.
    Software interrupts are usually implemented as instructions in the instruction set,
    which cause a context switch to an interrupt handler similarly to a hardware
    interrupt.
   Trap: A trap is a device or tactic intended to harm, capture, detect, or
    inconvenience an intruder. Traps may be physical objects, such as cages or snares,
    or metaphorical concepts.
   Monolithic System: A monolithic architecture is where processing, data
    and the user interface all reside on the same system
   System call / Monitor Call: a system call is the mechanism used by an
    application program to request service from the operating system.
   Kernal: The KERNAL is Commodore's name for the ROM-resident operating
    system core in its 8-bit home computers; from the original PET of 1977, via the
    extended, but strongly related, versions used in its successors; the VIC-20,
    Commodore 64, Plus/4, C16, and C128.
   Micro Kernal: A microkernel is a minimal computer operating system kernel
    providing only basic operating system services (system calls), while other
    services (commonly provided by kernels) are provided by user-space programs
    called servers.
   Device driver: A device driver, or a software driver is a specific type of
    computer software, typically developed to allow interaction with hardware
    devices.
   Command Line Interface: A command line interface or CLI is a tool for
    interacting with computers, often using a text terminal or remote shell client
    software, such as PuTTY
 GUI: A program interface that takes advantage of the computer's graphics capabilities to
  make the program easier to use.
 Resource: including
        o   Resource (Web), anything identified by a Uniform Resource Identifier
        o   Resource (Macintosh), data associated with a Mac OS file
        o   Resource (Windows), data embedded in EXE and DLL files
        o   Resource (Java), application data
   Shell: a shell is a piece of software that provides an interface for users
    (command line interpreter).
   Synchronization: Synchronization (or Sync) is a problem in timekeeping
    which requires the coordination of events to operate a system in unison.
   Process Control Block: A Process Control Block (PCB, also called Task
    Control Block or Task Struct) is a data structure in the operating system kernel
    containing the information needed to manage a particular process. The PCB is
    "the manifestation of a process in an operating system".[1]
   Thread: Threads are a way for a program to fork (or split) itself into two or
    more simultaneously (or pseudo-simultaneously) running tasks. Threads and
    processes differ from one operating system to another, but in general, the way that
    a thread is created and shares its resources is different from the way a process
    does.
   Short Term Schediling:Short term scheduling concerns with the allocation of
    CPU time to processes in order to meet some pre-defined system performance
    objectives. The definition of these objectives (scheduling policy) is an overall
    system design issue, and determines the ``character'' of the operating system from
    the user's (i.e. the buyer's) point of view, giving rise to the traditional distinctions
    among ``multi-purpose, time shared'', ``batch production'', ``real-time'' systems,
    and so on.
   Throughput: the rate of completion of processes (processes completed per unit
    time). This is a ``raw'' measure of how much work is performed, since it depends
    on the execution length of processes, but it's obviously affected by the scheduling
    policy.
   Long Term Scheduling: Long term scheduling: which determines which
    programs are admitted to the system for execution and when, and which ones
    should be exited.
 Medium Term Scheduling: Medium term scheduling: which determines when
  processes are to be suspended and resumed;
 Parent process: A parent process is a computer process that has created one or
  more child processes.
 Child Process: A child process is a computer process created by another process
  (the parent process).
 Interprocess Communication: Inter-Process Communication (IPC) is a set of
  techniques for the exchange of data between two or more threads in one or more
  processes. Processes may be running on one or more computers connected by a
  network. IPC techniques are divided into methods for message passing,
  synchronization, shared memory, and remote procedure calls (RPC).
 Response Time:the interval of time from the moment a service is requested until
  the response begins to be received. In time-shared, interactive systems this is a
  better measure of responsiveness from a user's point of view than turnaround
  time, since processes may begin to produce output early in their execution.
 Turnaround time: the interval between the submission of a process and the
  completion of its execution, including the actual running time, plus the time spent
  sleeping before being dispatched or while waiting to access various resources.
  This is the appropriate responsiveness measure for batch production, as well as
  for time-shared systems that maintain multiple batch queues, sharing CPU time
  among them.

				
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