UNIT 1 NOTES
Digital Computer A digital computer is an electronic computing machine that uses the binary digits (bits) 0 and 1 to represent all forms of information internally in digital form. Every computer has a set of instructions that define the basic functions it can perform. Sequences of these instructions.
Component of Digital Computer:
(1)CPU: The Central Processing Unit (CPU) or the processor is the portion of a computer system that carries out the instructions of a Computer, and is the primary element carrying out the computer's functions. This term has been in use in the computer industry at least since the early 1960s . The form, design and implementation of CPUs have changed dramatically since the earliest examples, but their fundamental operation remains much the same.
(2)ALU: an arithmetic logic unit (ALU) is a Digital computer that performs arthimatic and logical operations. The ALU is a fundamental building block of the central processing unit(CPU) of a computer, and even the simplest microprocessor contain one for purposes such as maintaining timers. The processors found inside modern CPUs and graphics processing units(CPU) accommodate very powerful and very complex ALUs; a single component may contain a number of ALUs.
Mathematician proposed the ALU concept in 1945, when he wrote a report on the foundations for a new computer called the EDVAC.
(3)Memory: memory is an organism's ability to store, retain, and recall information. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing the memory. The late nineteenth and early twentieth century put memory within the paradigms of cognitive psychology. In recent decades, it has become one of the principal pillars of a branch of science called cognitive neuroscience, an interdisciplinary link between cognitive psychology and neuroscience
(4) INPUT DEVICE:An input device is any peripheral (piece of computer hardware equipment) used to provide data and control signals to an information processing system (such as a computer
(5)OUTPUT DEVICE: An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.

Linux: Linux (commonly pronounced /ˈlɪnʌks/, LI-nuks in English,[5][6] also pronounced /ˈlɪnʊks/, LI-nooks[7]) is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration;[citation needed] typically all the underlying source code can be used, freely modified, and redistributed, both commercially and non-commercially, by anyone under licenses such as the GNU GPL.
Linux is predominantly known for its use in servers, although can be installed on a wide variety of computer hardware, ranging from embedded devices, mobile phones and even some watches[8] to mainframes and supercomputers.[9][10] Linux distributions, installed on both desktop and laptop computers, have become increasingly commonplace in recent years, partly owing to the popular Ubuntu distribution[11] and the emergence of netbooks.[12]
The name "Linux" comes from the Linux kernel, originally written in 1991 by Linus Torvalds. The full operating system usually comprises components such as utilities and libraries from the GNU Project (announced in 1983 by Richard Stallman), the X Window System, the GNOME and KDE desktop environments, and the Apache HTTP Server. Commonly-used applications with desktop Linux systems include the Mozilla Firefox web-browser and the OpenOffice.org office application suite. The GNU contribution is the basis for the Free Software Foundation's preferred name GNU/Linux

Unix: Unix (officially trademarked as UNIX, sometimes also written as UNIX with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna. Today the term Unix is used to describe any operating system that conforms to Unix standards, meaning the core operating system operates the same as the original Unix operating system. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.
As of 2007, the owner of the trademark is The Open Group, an industry standards consortium. Only systems fully compliant with and certified according to the Single UNIX Specification are qualified to use the trademark; others are called "Unix system-like" or "Unix-like".
During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix (particularly of the BSD variant, originating from the University of California, Berkeley) by commercial startups, the most notable of which are Mac OS X, Solaris, HP-UX and AIX. Today, in addition to certified Unix systems such as those already mentioned, Unix-like operating systems such as Linux and BSD are commonly encountered. The term "traditional Unix" may be used to describe a Unix or an operating system that has the characteristics of either Version 7 Unix or UNIX System V.

Structure Programming: Structured programming can be seen as a subset or subdiscipline of imperative programming, one of the major programming paradigms. It is most famous for removing or reducing reliance on the GOTO statement.
Historically, several different structuring techniques or methodologies have been developed for writing structured programs. The most common are:
1. Edsger Dijkstra's structured programming, where the logic of a program is a structure composed of similar sub-structures in a limited number of ways. This reduces understanding a program to understanding each structure on its own, and in relation to that containing it, a useful separation of concerns.
2. A view derived from Dijkstra's which also advocates splitting programs into sub-sections with a single point of entry, but is strongly opposed to the concept of a single point of exit.
3. Data Structured Programming or Jackson Structured Programming, which is based on aligning data structures with program structures. This approach applied the fundamental structures proposed by Dijkstra, but as constructs that used the high-level structure of a program to be modeled on the underlying data structures being processed. There are at least 3 major approaches to data structured program design proposed by Jean-Dominique Warnier, Michael A. Jackson, and Ken Orr.
The two latter meanings for the term "structured programming" are more common, and that is what this article will discuss. Years after Dijkstra (1969), object-oriented programming (OOP) was developed to handle very large or complex programs (see below: Object-oriented comparison
Programming Language: A programming language is an artificial language designed to express computations that can be performed by a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine, to express algorithms precisely, or as a mode of human communication.
Many programming languages have some form of written specification of their syntax (form) and semantics (meaning). Some languages are defined by a specification document. For example, the C programming language is specified by an ISO Standard. Other languages, such as Perl, have a dominant implementation that is used as a reference.
Programming language is classified in two ways
(1)High level: A high-level programming language is a programming language with strong abstraction from the details of the computer. In comparison to low-level programming languages, it may use natural language elements, be easier to use, or be more portable across platforms. Such languages hide the details of CPU operations such as memory access models and management of scope
(2)Low Level: a low-level programming language is a programming language that provides little or no abstraction from a computer's instruction set architecture. The word "low" refers to the small or nonexistent amount of abstraction between the language and machine language; because of this, low-level languages are sometimes described as being "close to the hardware."
A low-level language does not need a compiler or interpreter to run; the processor for which the language was written is able to run the code without using either of these.
By comparison, a high-level programming language isolates the execution semantics of a computer architecture from the specification of the program, making the process of developing a program simpler and more understandable.
Flow Chart: A flowchart is a diagrammatic representation of a step-by-step solution to a given problem. It is a common type of diagram, that represents an algorithm or process, showing the steps as boxes of various kinds, and their order by connecting these with arrows. Data is represented in these boxes, and arrows connecting them represent flow / direction of flow of data.
Symbols
A typical flowchart from older Computer Science textbooks may have the following kinds of symbols:
Start and end symbols
Represented as circles, ovals or rounded rectangles, usually containing the word "Start" or "End", or another phrase signaling the start or end of a process, such as "submit enquiry" or "receive product".
Arrows
Showing what's called "flow of control" in computer science. An arrow coming from one symbol and ending at another symbol represents that control passes to the symbol the arrow points to.
Processing steps
Represented as rectangles. Examples: "Add 1 to X"; "replace identified part"; "save changes" or similar.
Input/Output
Represented as a parallelogram. Examples: Get X from the user; display X.
Conditional or decision
Represented as a diamond (rhombus). These typically contain a Yes/No question or True/False test. This symbol is unique in that it has two arrows coming out of it, usually from the bottom point and right point, one corresponding to Yes or True, and one corresponding to No or False. The arrows should always be labeled. More than two arrows can be used, but this is normally a clear indicator that a complex decision is being taken, in which case it may need to be broken-down further, or replaced with the "pre-defined process" symbol.
A number of other symbols that have less universal currency, such as:
• A Document represented as a rectangle with a wavy base;
• A Manual input represented by parallelogram, with the top irregularly sloping up from left to right. An example would be to signify data-entry from a form;
• A Manual operation represented by a trapezoid with the longest parallel side at the top, to represent an operation or adjustment to process that can only be made manually.
• A Data File represented by a cylinder.
Flowcharts may contain other symbols, such as connectors, usually represented as circles, to represent converging paths in the flowchart. Circles will have more than one arrow coming into them but only one going out. Some flowcharts may just have an arrow point to another arrow instead. These are useful to represent an iterative process (what in Computer Science is called a loop). A loop may, for example, consist of a connector where control first enters, processing steps, a conditional with one arrow exiting the loop, and one going back to the connector. Off-page connectors are often used to signify a connection to a (part of another) process held on another sheet or screen. It is important to remember to keep these connections logical in order. All processes should flow from top to bottom and left to right.
Algorithm: [edit] Symbols
A typical flowchart from older Computer Science textbooks may have the following kinds of symbols:
Start and end symbols
Represented as circles, ovals or rounded rectangles, usually containing the word "Start" or "End", or another phrase signaling the start or end of a process, such as "submit enquiry" or "receive product".
Arrows
Showing what's called "flow of control" in computer science. An arrow coming from one symbol and ending at another symbol represents that control passes to the symbol the arrow points to.
Processing steps
Represented as rectangles. Examples: "Add 1 to X"; "replace identified part"; "save changes" or similar.
Input/Output
Represented as a parallelogram. Examples: Get X from the user; display X.
Conditional or decision
Represented as a diamond (rhombus). These typically contain a Yes/No question or True/False test. This symbol is unique in that it has two arrows coming out of it, usually from the bottom point and right point, one corresponding to Yes or True, and one corresponding to No or False. The arrows should always be labeled. More than two arrows can be used, but this is normally a clear indicator that a complex decision is being taken, in which case it may need to be broken-down further, or replaced with the "pre-defined process" symbol.
A number of other symbols that have less universal currency, such as:
• A Document represented as a rectangle with a wavy base;
• A Manual input represented by parallelogram, with the top irregularly sloping up from left to right. An example would be to signify data-entry from a form;
• A Manual operation represented by a trapezoid with the longest parallel side at the top, to represent an operation or adjustment to process that can only be made manually.
• A Data File represented by a cylinder.
Flowcharts may contain other symbols, such as connectors, usually represented as circles, to represent converging paths in the flowchart. Circles will have more than one arrow coming into them but only one going out. Some flowcharts may just have an arrow point to another arrow instead. These are useful to represent an iterative process (what in Computer Science is called a loop). A loop may, for example, consist of a connector where control first enters, processing steps, a conditional with one arrow exiting the loop, and one going back to the connector. Off-page connectors are often used to signify a connection to a (part of another) process held on another sheet or screen. It is important to remember to keep these connections logical in order. All processes should flow from top to bottom and left to right.
Algorithm: an algorithm is an effective method for solving a problem using a finite sequence of instructions. Algorithms are used for calculation, data processing, and many other fields.
Each algorithm is a list of well-defined instructions for completing a task. Starting from an initial state, the instructions describe a computation that proceeds through a well-defined series of successive states, eventually terminating in a final ending state. The transition from one state to the next is not necessarily deterministic; some algorithms, known as randomized algorithms, incorporate randomness. an algorithm is an effective method for solving a problem using a finite sequence of instructions. Algorithms are used for calculation, data processing, and many other fields.
Each algorithm is a list of well-defined instructions for completing a task. Starting from an initial state, the instructions describe a computation that proceeds through a well-defined series of successive states, eventually terminating in a final ending state. The transition from one state to the next is not necessarily deterministic; some algorithms, known as randomized algorithms, incorporate randomness.
Example:Addition of two no
Step(1):Read A,B
Step(2)Add A,B
Step(3)C=A+B
Step(4)end