计算机科学概论重点

1. Real-time processing⏹The interactive systems required that the activities taking place in a machine becoordinated with the activities in the machine’s environment.⏹This coordination called real-time processing.⏹It could not support to serve more than one user.Time-sharing processing⏹The operating system rotated the various jobs in and out of execution by aprocess called time-sharing.⏹It is the technique of dividing time into intervals , or time slices, and restrictingthe execution of a job to only one time slice at a time, one by one.⏹Multitasking processing⏹Time-sharing used in single user system called multitasking processing⏹Advantage of time-sharing processing⏹By rapidly shuffling the jobs in this manner, the illusion of several jobs executingsimultaneously is created.⏹By it, the computer system does not spend much of its time waiting for peripheraldevices to complete tasks or for a user to make the next request.⏹The two broad categories of machine’s software⏹Application software⏹System software⏹Application software⏹Consist of the programs for performing tasks particular to the machines’sutilization.⏹Examples of application software include spreadsheets, database systems,desktop publishing systems, program development software, and games.⏹System software⏹It perform those tasks that are common to computer system in general. Providingthe environment for the application software.⏹System software can divided into two categories: operating system and utilitysoftware.⏹Utility software⏹Consist of program for performing activities that are fundamental to computerinstallations yet not included in the operating system.⏹It consist of software units that extend the capabilities of the operating system.⏹Utility software examples: the software formatting a disk, copying a file,communicating through a modem over telephone lines, compressing anddecompressing data, handing network communication.⏹Shell⏹The portion of operating system that define the interface between the operatingsystem and its user⏹Kernel⏹The internal part of an operating system, which contains those softwarecomponents that perform the very basic functions required by the computerinstallation.⏹Window manager and its functions⏹ A major component within today’s GUI⏹Allocating blocks of space on the screen –window, and keep track of whichapplication is associated with each window⏹Placing the desired pattern in the window assigned to an application, andmonitoring mouse’s moving and acting.⏹File manager⏹Its job is to coordinate the use of machi ne’ mass storage facilities.⏹Directory or folder: grouped file bundle⏹User can organize their files according to their purposes by placing related filesin the same directory.⏹Directory can set up in hierarchic structure, including directory and subdirectory⏹Path: a chain of directories within directories is called directory path⏹File descriptor:an area of main memory, where stored information needed tofind and manipulate the fileVirtual Memory: an illusionary memory area by rotating programs and data back and forth between main memory and mass storage.Page: memory unit, typical page size is no more than four KB⏹Scheduler⏹It determines which activities are to be considered for execution in a time-sharingsystem⏹Dispatcher⏹It controls the allocation of time slices to these activities⏹Boot Strapping (or booting)⏹ A procedure is performed by the machine each time it is turn on.⏹ A CPU is designed so that its program counter starts with a particularpredetermined address each time the CPU is turn on⏹At that address, the CPU expects to find the first instruction to be executed.⏹The contents of that memory is permanent, the memory is read-only memory(ROM)⏹Bootstrap⏹ A small program that is executed automatically when the machine is turned on⏹What is a process⏹ A process is the activity of executing a program.⏹Process State⏹ A process encompasses the current status of the activity, called process state⏹Process state includes:1) the current position in the program being executed,value of the program counter.2) the values in the other registers and the associated memory cells.⏹The difference between program and process⏹The program is merely a static set of directions, but the process is a dynamicactivity whose properties change as time progresses⏹ A program can be associated with more than one process at the same time.⏹Process table⏹It is a block of information in main memory used by scheduler to keep track ofall the processes.⏹When a new task is assigned to the machine, the scheduler creates a process forthe task by placing a new entry in the process table⏹One entry contains :1) the memory area assigned to the process;2) the priority of the process;3) whether the process is ready or waiting.⏹State of a process--Ready and Waiting⏹Ready state indicates the process is in a state in which its progress can continue⏹Waiting state indicates the process’s progress is currently delayed until someexternal event occurs, such as the completion of a hard access or the arrival of amessage from another process.⏹Interrupt⏹It is a signal generated by the timer circuit at the end of one time slice.⏹When the CPU receives an interrupt signal, it complete its current machine cycle,saves its position in the current process, and beings executing a program, calledthe interrupt handler.⏹interrupt handler⏹It is a part of dispatcher and is stored in main memory⏹Based on area or distance that a network covers⏹Local Area Networks (LANs)A LAN normally consists of a collection of computers in a single building or building complex.⏹Wide Area Networks( WANs)A WAN links machines that may be in neighboring cites or on opposite sides of the world.⏹Bridge⏹It is a coupling device of connecting two networks which are compatible.⏹When two networks are connected via a bridge, the result is simply a large singlenetwork⏹The connection between two networks to form an internet is handled by amachine known as Router.⏹Router connects network which are not compatible and must convert between theidiosyncrasies of the two original networks⏹The original networks maintain their individuality and just send message between twonetworks⏹Primitive and relative concepts⏹The primitives is a set of well-defined building block from which algorithmrepresentation can be constructed precisely and in a uniform level of detail⏹Each primitive consist of two parts: Syntax and Semantics⏹Syntax: refer to the primitive’s symbolic representation⏹Semantics: refer to the concept represented, or the meaning of the primitive.⏹Programming language⏹It is a collection of primitives along with a collection of rules stating how theprimitives can be combined to represent more complex ideas.⏹Machine’s language: is a collection of “lower-level” primitive. If an algorithmis expressed by which, we will certainly have a program suitable for machineexecution.⏹Formal Programming Language:is a collection of “higher-level” primitives,each being an abstract tool constructed from the “lower-level” primitivesprovided in the machine’s language⏹By a formal programming language, an algorithm can be expressed in aconceptually higher form than in the actual machine language⏹What is the Pseudocode⏹It is a notational system in which ideas can be expressed informally during thealgorithm development process.⏹How to obtain a Pseudocode⏹One way is simply to loosen the rules of the formal language in which the finalversion of the algorithm is to be expressed.⏹Another way is to develop a consistent, concise notation for representingrecurring semantic structure. In turn , these structure will become the primitivesin which we attempt to express future ideas⏹The second generation: assembly language-1⏹What ia an assembly language⏹ A mnemonic system for representing programs is collectively called an assemblylanbguage⏹How does an assembly language⏹Using a mnemonic system which consist of a set of descriptive names(identifiers) and rules substitutes for machine codes⏹Using a programs (assemblers) to translate the mnemonic form intomachine-compatible form⏹The second generation: assembly language-2⏹Advantage⏹It is analogue to pseudocode and is easy to remember.⏹It is a giant step forward in the search for better programming techniques.⏹Disadvantage⏹The primitives are the same as those found in the corresponding machinelanguage. The difference is simply in the syntax used to represent them, so it isstill machine dependent⏹Using it, a programmer is still forced to think in terms of the small, incrementalsteps of machine’s language⏹ A programmer approaches a problem by considering the input that is given, theoutput that is desired, and the transformation that is required to produce theoutput from the given input.⏹The programming process is that of constructing functions as nested complexesof simpler function.⏹An advantage is that it encourages a modular approach to program construction,may be from previously established pieces.⏹The Object-Oriented Paradigm⏹It leads to the programming process called object-oriented programming (OOP)⏹In this approach, units of data are viewed as active “objects” rather than thepassive units envisioned by the traditional imperative paradigm.⏹The objects have their data and procedures. Other programs just need to sendmessage to them without needing to contain some algorithms, and the objectsknow how to response the certain events by executing right procedures.Two examples: Textbook P234⏹Advantage or characteristics:modular structure, reusable, message communication and event driven⏹What is declarative sentence⏹Defining customized terminology that is used later in the program, such as namesused to reference data items.⏹Issues of declarative sentence⏹Variables, Constants, and Literals⏹Data type⏹Data structure⏹Operator overloading⏹Using one symbol to represent more than one type of operation, and the meaningof the symbol is determined by the data type of the operands.⏹What is the Control Statement?⏹It is an imperative statement.⏹It alters the execution sequence of the program.⏹Structured programming⏹It encompasses an organized design methodology combined with the appropriateuse of the language’s control statement.⏹What is the Comment?⏹It is explanatory statement to insert within a program to help understanding thatprogram.⏹Role of the Comment⏹Enhancing the readability of a program by explaining its esoteric feature in amore human compatible form⏹The importance of the Comment⏹Because comments are ignored by a translator, it is not important from amachine’s point of view⏹From human’s point of view, it is very important part of a program⏹The form of the Comment⏹One is to bracket the entire comment by special markets, one at the beginning ofthe comment and one at the end.⏹Other is to mark the beginning of the comment and allow the comment to occupythe reminder of the line to the right of the market⏹What is the Procedures?⏹It is program unit written independently of other program units yet associatedwith them through a transfer/return process.⏹How does a Procedures work?⏹When It is required to work, control is transferred to it, and control will return tothe original program unit after it has finished. (See figure 6.10)⏹The process is referred to as calling or invoking the procedure⏹The structure of a Procedures⏹Header: identifying the name of the procedure and other things such as,parameter, (type of return value)⏹Body: is a procedure’s detail• declaration statement: variables and constant• imperative statement: the steps to be performed⏹Parameters⏹The data items transfer between a procedure and its calling program unit⏹Parameter are listed in invoking statement and procedure header, and they areassociated each other entry by entry⏹Formal parameters⏹The parameters listed in procedure header are called formal parameters⏹They represent slots into which specific data will be plugged when theprocedure’s actions are required.⏹Actual parameters⏹The parameters listed in calling units are called actual parameters⏹They represent the actual values to be used.⏹Two methods to pass parameters from actual parameters to formal parameters⏹Passing data by value⏹Passing data by reference⏹By value⏹By duplicating the data, and allowing the procedure to manipulate only the copyof original data⏹Protecting the original data from mistakenly altered, but it is inefficient in case oflarge blocks of data (see figure 6.12)⏹By reference⏹To allow the procedure direct access to the actual parameters by tell it the addressof the actual parameters⏹It is more efficient than by value, and it will change original values⏹What is the function⏹ A program unit similar to a procedure⏹ A value is transferred back to the calling program as “the value of the function”rather than via the parameter list.⏹What is the Translation Process?⏹The process of converting a program from one language to another.⏹Three activities of the translation process⏹Lexical analysis⏹Parsing⏹Code generation⏹Three units of the translator⏹Lexical analyzer⏹Parser⏹Code generator⏹Code generation⏹It is process of constructing the machine-language instructions to simulate thestatements recognized by the parser.⏹Code optimization: to produce efficient code.。