Repair & Mainteinance

Unit-1
Introduction

Definition of Computer:-

Computer is an electronic device that accepts data & information process them & gives processed output as information. The word “computer” means “something that computes or “Calculate”. It may be defined as a device that can operate upon data or information which is done through the execution of a program.

Computer typically performs work in three well defined steps:-
- Accepting inputs.
- Processing rules (program), &
- Producing output.

Data & Information:-

Data is a collection of facts unorganized, but able to be organized into useful information. Data is a raw material of information.

A collection of class attendance cards is an example. Data can be manipulated to produce output as student attendance reports. This output is called as information, in organized facts that help people to make decision.

Data is a raw material used as input to data processing.

Program:-

A program is a sequence of instruction which operate on data to perform certain task.

Software:-

Computer software or simply software is any set of machine-readable instructions that directs a computer's processor to perform specific operations. Without software computer is useless For example: Using browser (software) you are able to surf internet, by using anti-virus (software) you are able to protect your computer from viruses, by using Operating System (Software) we are able to use computer etc.

Hardware:-

Computer hardware is the collection of physical elements that constitutes a computer system. Computer hardware is the physical parts or components of a computer, such as the monitor, mouse, keyboard, computer data storage, hard disk drive (HDD), system unit (graphic cards, sound cards, memory, motherboard and chips), and so on, all of which are physical objects that can be touched (that is, they are tangible). In contrast, software is instructions that can be stored and run by hardware.

Unit-2
Types of Computer

Analog Computer:-

Analog computers are used to process analog data. Analog data is of continuous nature and which is not discrete or separate. Such type of data includes temperature, pressure, speed, weight, voltage, depth etc. These quantities are continuous and having an infinite variety of values. It measures continuous changes in some physical quantity e.g. The Speedometer of a car measures speed, the change of temperature is measured by a Thermometer, the weight is measured by Weights machine. These computers are ideal in situations where data can be accepted directly from measuring instrument without having to convert it into numbers or codes. Analog computers are widely used for certain specialized engineering and scientific applications, for calculation and measurement of analog quantities.

Digital Computer:-

A Digital Computer, as its name implies, works with digits to represent numerals, letters or other special symbols. Digital Computers operate on inputs which are ON-OFF type and its output is also in the form of ON-OFF signal. Normally, an ON is represented by a 1 and an OFF is represented by a 0. So we can say that digital computers process information which is based on the presence or the absence of an electrical charge or we prefer to say a binary 1 or 0.

A digital computer can be used to process numeric as well as non-numeric data. It can perform arithmetic operations like addition, subtraction, multiplication and division and also logical operations. Most of the computers available today are digital computers. The most common examples of digital computers are accounting machines and calculators. The results of digital computers are more accurate than the results of analog computers. Analog computers are faster than digital. Analog computers lack memory whereas digital computers store information. We can say that digital computers count and analog computers measures.

Hybrid Computer:-

A hybrid is a combination of digital and analog computers. It combines the best features of both types of computers, i-e. It has the speed of analog computer and the memory and accuracy of digital computer. Hybrid computers are used mainly in specialized applications where both kinds of data need to be processed. Therefore, they help the user, to process both continuous and discrete data. For example a petrol pump contains a processor that converts fuel flow measurements into quantity and price values. In hospital Intensive Care Unit (ICU), an analog device is used which measures patient's blood pressure and temperature etc, which are then converted and displayed in the form of digits.

Super Computer:-

A supercomputer is a computer with a high-level computational capacity. Performance of a supercomputer is measured in floating point operations per second (FLOPS). As of 2015, there are supercomputers which can perform up to quadrillions of FLOPS.

"The Blue Gene/P supercomputer at Argonne National Lab runs over 250,000 processors using normal data center air conditioning, grouped in 72 racks/cabinets connected by a high-speed optical network"

Supercomputers were introduced in the 1960s, made initially, and for decades primarily, by Seymour Cray at Control Data Corporation (CDC), Cray Research and subsequent companies bearing his name or monogram. While the supercomputers of the 1970s used only a few processors, in the 1990s machines with thousands of processors began to appear and, by the end of the 20th century, massively parallel supercomputers with tens of thousands of "off-the-shelf" processors were the norm. Since its introduction in June 2013, China's Tianhe-2 supercomputer is currently the fastest in the world at 33.86 petaFLOPS (PFLOPS), or 33.86 quadrillions of FLOPS.

Mainframe Computer:-

Mainframe computers are computers used primarily by large organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning and transaction processing.

The term originally referred to the large cabinets called "main frames" that housed the central processing unit and main memory of early computers. Later, the term was used to distinguish high-end commercial machines from less powerful units. Most largescale computer system architectures were established in the 1960s, but continue to evolve. Modern mainframe design is generally less defined by single-task computational speed (typically defined as MIPS rate or FLOPS in the case of floating point calculations), and more by:
- Redundant internal engineering resulting in high reliability and security
- Extensive input-output facilities with the ability to offload to separate engines
- Strict backward compatibility with oldersoftware
- High hardware and computational utilization rates through virtualization to support massive throughput.

Their high stability and reliability enables these machines to run uninterrupted for decades.

Mini Computer:-

A minicomputer, is a class of smaller computers that developed in the mid-1960s. In a 1970 survey, the New York Times suggested a consensus definition of a minicomputer as a machine costing less than 25,000 USD, with an input-output device such as a teleprinter and at least four thousand words of memory, that is capable of running programs in a higher level language, such as Fortran or BASIC. The class formed a distinct group with its own software architectures and operating systems. Minis were designed for control, instrumentation, human interaction, and communication switching as distinct from calculation and record keeping. During the two decade lifetime of the minicomputer class (1965-1985), almost 100 companies formed and only a half dozen remained.

Some popular mini computers in current date are:-
- Samsung NC10 NC20 och,
- Acer Aspire One A150-B,
- MSI Wind U100,
- Asus Eee PC 901,
- HP Compaq Mini 730eo, etc.

Microcomputer:-

A microcomputer is a small, relatively inexpensive computer with a microprocessor as its central processing unit (CPU). It includes a microprocessor, memory, and input/output (I/O) facilities. Microcomputers became popular in the 1970s and 80s with the advent of increasingly powerful microprocessors. The predecessors to these computers, mainframes and minicomputers, were comparatively much larger and more expensive.

Some popular microcomputers are:-
- Intel SIM8-01,
- Motorola MEK6800D2,
- Rockwell AIM-65,
- Synertek SYM-1, &
- Intel SDK-85, etc