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NEW AND AMAZING SPACE Technology: How to Find Dangerous Asteroids

Searching for potentially Earth-destroying asteroids today isn't easy.
They're dark, difficult to see from the surface of the planet, and there are a lot of them floating in the solar system. Scientists are now looking into new, higher-tech ways to find and track near-Earth objects, but for now, much of the hard work of asteroid tracking is done the old-fashioned way: with a telescope on a clear night.
NASA scientists, astronomers around the world and amateur observers with backyard telescopes devote their lives and free time to seeking out potentially hazardous near-Earth objects (NEOs). [Photos: Potentially Dangerous Asteroids]

"It all begins with an observer making observations," Gareth Williams, of the Minor Planet Center, the clearinghouse for asteroid and other minor-planet documentation, told SPACE.com "They can be observing known objects, or they can be searching for new objects, but even if they're searching for known objects — just to take a pretty picture or some reason — new objects can come into the field. About one in 1,000 of these new objects turn out to be an object that's moving anomalously when compared to other objects in the frame."
Hunting asteroids
Anomalous motion — when an object moves in a different way than other bodies in a frame — can signal something to a keen observer. The skywatcher then reports his or her findings to the Minor Planet Center (MPC), located in Cambridge, Mass., and officials with the MPC search the organization's database to try to find a match with known, already-tracked objects.
If the new observation doesn't match any known object, the MPC puts it onto the NEO confirmation page — a database where observers can find information about asteroids with orbits that have not been sufficiently traced.
The MPC functions as the central database for all information about NEOs. The astronomers of the MPC — run by the International Astronomical Union — collect and help verify all of the space-rock sightings that are reported.
An interconnected group of observers and sky surveys work to validate claims of near-Earth-object sightings on a daily basis. This month alone, observers have discovered 80 NEOs out of 656,546 observations.

Europe Launches New Project Space Metal 3D Printing

"We want to build the best quality metal products ever made," David Jarvis, ESA's Head of New Materials and Energy Research, said in a statement when the project was unveiled last week at the London Science Museum.
The group is focusing on making space-quality components by using lasers, electron beams and even plasma to melt metal alloys, Jarvis explained. The project also aims to explore the possibility of combining strong and lightweight, but more exotic metals, such as tungsten, niobium and platinum, though these materials are expensive.
As part of the initiative, four pilot 3D printing-factories are being established in Germany, Italy, Norway and the United Kingdom. David wants to help standardize the technique and bring it to the mainstream, connecting key players in the metallic 3D printing business to develop a supply chain.
ESA officials say innovations along the way to make 3D printers more viable for spacecraft could have benefits on Earth, leading to improvements in aircraft wings, jet engines and automotive systems.
ESA is hardly alone in its ambition to perfect metal 3D printing for the final frontier. Among several other NASA endeavors in additive manufacturing, the U.S. space agency recently completed a successful hot-fire test of the biggest 3D-printed rocket part built to date: an engine injector printed with nickel-chromium alloy powder.
There are several private and university-led efforts, too. Earlier this month, a group of students at the University of California, San Diego performed their first test of a 3D-printed engine made from cobalt chromium.

Introduction to Computers and Information Technology

A computer is a general purpose device that can be programmed to carry out a set of arithmetic or logical operations. Since a sequence of operations can be readily changed, the computer can solve more than one kind of problem.
Conventionally, a computer consists of at least one processing element, typically a central processing unit (CPU) and some form of memory. The processing element carries out arithmetic and logic operations, and a sequencing and control unit that can change the order of operations based on stored information. Peripheral devices allow information to be retrieved from an external source, and the result of operations saved and retrieved.
The first electronic digital computers were developed between 1940 and 1945. Originally they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).^[1] In this era mechanical analog computers were used for military applications.
Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space.^[2] Simple computers are small enough to fit into mobile devices, and mobile computers can be powered by small batteries. Personal computers in their various forms are icons of the Information Age and are what most people think of as “computers.” However, the embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are the most numerous.

History of computing

Etymology

The first recorded use of the word “computer” was in 1613 in a book called “The yong mans gleanings” by English writer Richard Braithwait I haue read the truest computer of Times, and the best Arithmetician that euer breathed, and he reduceth thy dayes into a short number. It referred to a person who carried out calculations, or computations, and the word continued with the same meaning until the middle of the 20th century. From the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations.^[3]

Mechanical aids to computing

The history of the modern computer begins with two separate technologies, automated calculation and programmability. However no single device can be identified as the earliest computer, partly because of the inconsistent application of that term^[4]. A few precusors are worth mentioning though, like some mechanical aids to computing, which were very successful and survived for centuries until the advent of the electronic calculator, like the Sumerian abacus, designed around 2500 BC^[5] of which a descendant won a speed competition against a contemporary desk calculating machine in Japan in 1946,^[6] the slide rules, invented in the 1620s, which were carried on five Apollo space missions, including to the moon^[7] and arguably the astrolabe and the Antikythera mechanism, an ancient astronomical analog computer built by the Greeks around 80 BC.^[8] The Greek mathematician Hero of Alexandria (c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when.^[9] This is the essence of programmability.

Mechanical calculators and programmable looms

Blaise Pascal invented the mechanical calculator in 1642,^[10] known as Pascal's calculator, it was the first machine to better human performance of arithmetical computations^[11] and would turn out to be the only functional mechanical calculator in the 17th century.^[12] Two hundred years later, in 1851, Thomas de Colmar released, after thirty years of development, his simplified arithmometer; it became the first machine to be commercialized because it was strong enough and reliable enough to be used daily in an office environment. The mechanical calculator was at the root of the development of computers in two separate ways. Initially, it was in trying to develop more powerful and more flexible calculators^[13] that the computer was first theorized by Charles Babbage^[14][15] and then developed.^[16] Secondly, development of a low-cost electronic calculator, successor to the mechanical calculator, resulted in the development by Intel^[17] of the first commercially available microprocessor integrated circuit.
In 1801, Joseph Marie Jacquard made an improvement to the textile loom by introducing a series of punched paper cards as a template which allowed his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.

First use of punched paper cards in computing

The Most Famous Image in the Early History of Computing^[18]

This portrait of Jacquard was woven in silk on a Jacquard loom and required 24,000 punched cards to create (1839). It was only produced to order. Charles Babbage started exhibiting this portrait in 1840 to explain how his analytical engine would work.^[19]

It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer, his analytical engine.^[20] Limited finances and Babbage's inability to resist tinkering with the design meant that the device was never completed—nevertheless his son, Henry Babbage, completed a simplified version of the analytical engine's computing unit (the mill) in 1888. He gave a successful demonstration of its use in computing tables in 1906. This machine was given to the Science museum in South Kensington in 1910.

Ada Lovelace, considered to be the first computer programmer^[21]

Between 1842 and 1843, Ada Lovelace, an analyst of Charles Babbage's analytical engine, translated an article by Italian military engineer Luigi Menabrea on the engine, which she supplemented with an elaborate set of notes of her own. These notes contained what is considered the first computer program – that is, an algorithm encoded for processing by a machine. She also stated: “We may say most aptly, that the Analytical Engine weaves algebraical patterns just as the Jacquard-loom weaves flowers and leaves.”; furthermore she developed a vision on the capability of computers to go beyond mere calculating or number-crunching^[22] claiming that: should “...the fundamental relations of pitched sounds in the science of harmony and of musical composition...” be susceptible “...of adaptations to the action of the operating notation and mechanism of the engine...” it “...might compose elaborate and scientific pieces of music of any degree of complexity or extent”.^[23]
In the late 1880s, Herman Hollerith invented the recording of data on a machine-readable medium. Earlier uses of machine-readable media had been for control, not data. “After some initial trials with paper tape, he settled on punched cards...”^[24] To process these punched cards he invented the tabulator, and the keypunch machines. These three inventions were the foundation of the modern information processing industry. Large-scale automated data processing of punched cards was performed for the 1890 United States Census by Hollerith's company, which later became the core of IBM. By the end of the 19th century a number of ideas and technologies, that would later prove useful in the realization of practical computers, had begun to appear: Boolean algebra, the vacuum tube (thermionic valve), punched cards and tape, and the teleprinter.

First general-purpose computers

The Zuse Z3, 1941, considered the world's first working programmable, fully automatic computing machine.

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.
Alan Turing is widely regarded as the father of modern computer science. In 1936, Turing provided an influential formalization of the concept of the algorithm and computation with the Turing machine, providing a blueprint for the electronic digital computer.^[25] Of his role in the creation of the modern computer, Time magazine in naming Turing one of the 100 most influential people of the 20th century, states: “The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine.”^[25]

The ENIAC, which became operational in 1946, is considered to be the first general-purpose electronic computer. Programmers Betty Jean Jennings (left) and Fran Bilas (right) are depicted here operating the ENIAC's main control panel.

EDSAC was one of the first computers to implement the stored-program (von Neumann) architecture.

The first really functional computer was the Z1, originally created by Germany's Konrad Zuse in his parents living room in 1936 to 1938, and it is considered to be the first electro-mechanical binary programmable (modern) computer.^[26]
George Stibitz is internationally recognized as a father of the modern digital computer. While working at Bell Labs in November 1937, Stibitz invented and built a relay-based calculator he dubbed the “Model K” (for “kitchen table,” on which he had assembled it), which was the first to use binary circuits to perform an arithmetic operation. Later models added greater sophistication including complex arithmetic and programmability.^[27]
The Atanasoff–Berry Computer (ABC) was the world's first electronic digital computer, albeit not programmable.^[28] Atanasoff is considered to be one of the fathers of the computer.^[29] Conceived in 1937 by Iowa State College physics professor John Atanasoff, and built with the assistance of graduate student Clifford Berry,^[30] the machine was not programmable, being designed only to solve systems of linear equations. The computer did employ parallel computation. A 1973 court ruling in a patent dispute found that the patent for the 1946 ENIAC computer derived from the Atanasoff–Berry Computer.
The first program-controlled computer was invented by Konrad Zuse, who built the Z3, an electromechanical computing machine, in 1941.^[31] The first programmable electronic computer was the Colossus, built in 1943 by Tommy Flowers.

Key steps towards modern computers

A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as “the first digital electronic computer” is difficult.^{Shannon 1940} Notable achievements include:

• Konrad Zuse's electromechanical “Z machines.” The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.^[32] Thus, Zuse is often regarded as the inventor of the computer.^{[33][34][35][36]}
• The non-programmable Atanasoff–Berry Computer (commenced in 1937, completed in 1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory. The use of regenerative memory allowed it to be much more compact than its peers (being approximately the size of a large desk or workbench), since intermediate results could be stored and then fed back into the same set of computation elements.
• The secret British Colossus computers (1943),^[37] which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically re-programmable. It was used for breaking German wartime codes.
• The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.^[38]
• The U.S. Army's Ballistic Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an architecture which required rewiring a plugboard to change its programming.

Stored-program architecture

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Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the “stored-program architecture” or von Neumann architecture. This design was first formally described by John von Neumann in the paper First Draft of a Report on the EDVAC, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of which was completed in 1948 at the University of Manchester in England, the Manchester Small-Scale Experimental Machine (SSEM or “Baby”). The Electronic Delay Storage Automatic Calculator (EDSAC), completed a year after the SSEM at Cambridge University, was the first practical, non-experimental implementation of the stored-program design and was put to use immediately for research work at the university. Shortly thereafter, the machine originally described by von Neumann's paper—EDVAC—was completed but did not see full-time use for an additional two years.
Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word “computer” is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.

Die of an Intel 80486DX2 microprocessor (actual size: 12×6.75 mm) in its packaging

Beginning in the 1950s, Soviet scientists Sergei Sobolev and Nikolay Brusentsov conducted research on ternary computers, devices that operated on a base three numbering system of -1, 0, and 1 rather than the conventional binary numbering system upon which most computers are based. They designed the Setun, a functional ternary computer, at Moscow State University. The device was put into limited production in the Soviet Union, but supplanted by the more common binary architecture.

Semiconductors and microprocessors

Computers using vacuum tubes as their electronic elements were in use throughout the 1950s, but by the 1960s they had been largely replaced by transistor-based machines, which were smaller, faster, cheaper to produce, required less power, and were more reliable. The first transistorized computer was demonstrated at the University of Manchester in 1953.^[39] In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the late 1970s, many products such as video recorders contained dedicated computers called microcontrollers, and they started to appear as a replacement to mechanical controls in domestic appliances such as washing machines. The 1980s witnessed home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household.^{[citation needed]}
Modern smartphones are fully programmable computers in their own right, and as of 2009 may well be the most common form of such computers in existence.^{[citation needed]}

Programs

Alan Turing was an influential computer scientist.

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that some type of instructions (the program) can be given to the computer, and it will process them. Modern computers based on the von Neumann architecture often have machine code in the form of an imperative programming language.
In practical terms, a computer program may be just a few instructions or extend to many millions of instructions, as do the programs for word processors and web browsers for example. A typical modern computer can execute billions of instructions per second (gigaflops) and rarely makes a mistake over many years of operation. Large computer programs consisting of several million instructions may take teams of programmers years to write, and due to the complexity of the task almost certainly contain errors.

Stored program architecture

Main articles: Computer program and Computer programming

Replica of the Small-Scale Experimental Machine (SSEM), the world's first stored-program computer, at the Museum of Science and Industry in Manchester, England

This section applies to most common RAM machine-based computers.
In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. These instructions are read from the computer's memory and are generally carried out (executed) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called “jump” instructions (or branches). Furthermore, jump instructions may be made to happen conditionally so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers directly support subroutines by providing a type of jump that “remembers” the location it jumped from and another instruction to return to the instruction following that jump instruction.
Program execution might be likened to reading a book. While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.
Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time, with a near certainty of making a mistake. On the other hand, a computer may be programmed to do this with just a few simple instructions. For example:

      mov No. 0, sum     ; set sum to 0
      mov No. 1, num     ; set num to 1
loop: add num, sum    ; add num to sum
      add No. 1, num     ; add 1 to num
      cmp num, #1000  ; compare num to 1000
      ble loop        ; if num <= 1000, go back to 'loop'
      halt            ; end of program. stop running

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in about a millionth of a second.^[40]

Bugs

Main article: Software bug

The actual first computer bug, a moth found trapped on a relay of the Harvard Mark II computer

Errors in computer programs are called “bugs.” They may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases, they may cause the program or the entire system to “hang,” becoming unresponsive to input such as mouse clicks or keystrokes, to completely fail, or to crash. Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an exploit, code designed to take advantage of a bug and disrupt a computer's proper execution. Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design.^[41]
Admiral Grace Hopper, an American computer scientist and developer of the first compiler, is credited for having first used the term “bugs” in computing after a dead moth was found shorting a relay in the Harvard Mark II computer in September 1947.^[42]

Machine code

In most computers, individual instructions are stored as machine code with each instruction being given a unique number (its operation code or opcode for short). The command to add two numbers together would have one opcode, the command to multiply them would have a different opcode and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from, each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs (which are just lists of these instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer in the same way as numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program, architecture. In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.
While it is possible to write computer programs as long lists of numbers (machine language) and while this technique was used with many early computers,^[43] it is extremely tedious and potentially error-prone to do so in practice, especially for complicated programs. Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember – a mnemonic such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's assembly language. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler.

A 1970s punched card containing one line from a FORTRAN program. The card reads: “Z(1) = Y + W(1)” and is labeled “PROJ039” for identification purposes.

Programming language

Main article: Programming language

Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. They are generally either translated into machine code by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Sometimes programs are executed by a hybrid method of the two techniques.

Low-level languages

Main article: Low-level programming language

Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) tend to be unique to a particular type of computer. For instance, an ARM architecture computer (such as may be found in a PDA or a hand-held videogame) cannot understand the machine language of an Intel Pentium or the AMD Athlon 64 computer that might be in a PC.^[44]

Higher-level languages

Main article: High-level programming language

Though considerably easier than in machine language, writing long programs in assembly language is often difficult and is also error prone. Therefore, most practical programs are written in more abstract high-level programming languages that are able to express the needs of the programmer more conveniently (and thereby help reduce programmer error). High level languages are usually “compiled” into machine language (or sometimes into assembly language and then into machine language) using another computer program called a compiler.^[45] High level languages are less related to the workings of the target computer than assembly language, and more related to the language and structure of the problem(s) to be solved by the final program. It is therefore often possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various video game consoles.

Program design

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Program design of small programs is relatively simple and involves the analysis of the problem, collection of inputs, using the programming constructs within languages, devising or using established procedures and algorithms, providing data for output devices and solutions to the problem as applicable. As problems become larger and more complex, features such as subprograms, modules, formal documentation, and new paradigms such as object-oriented programming are encountered. Large programs involving thousands of line of code and more require formal software methodologies. The task of developing large software systems presents a significant intellectual challenge. Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult; the academic and professional discipline of software engineering concentrates specifically on this challenge.

Components

Main articles: Central processing unit and Microprocessor

A general purpose computer has four main components: the arithmetic logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by buses, often made of groups of wires.
Inside each of these parts are thousands to trillions of small electrical circuits which can be turned off or on by means of an electronic switch. Each circuit represents a bit (binary digit) of information so that when the circuit is on it represents a “1”, and when off it represents a “0” (in positive logic representation). The circuits are arranged in logic gates so that one or more of the circuits may control the state of one or more of the other circuits.
The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.

Control unit

Main articles: CPU design and Control unit

Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.

The control unit (often called a control system or central controller) manages the computer's various components; it reads and interprets (decodes) the program instructions, transforming them into a series of control signals which activate other parts of the computer.^[46] Control systems in advanced computers may change the order of some instructions so as to improve performance.
A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.^[47]
The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:

1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
3. Increment the program counter so it points to the next instruction.
4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
8. Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as “jumps” and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).
The sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program, and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer, which runs a microcode program that causes all of these events to happen.

Arithmetic logic unit (ALU)

Main article: Arithmetic logic unit

The ALU is capable of performing two classes of operations: arithmetic and logic.^[48]
The set of arithmetic operations that a particular ALU supports may be limited to addition and subtraction, or might include multiplication, division, trigonometry functions such as sine, cosine, etc., and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers, albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other (“is 64 greater than 65?”).
Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful for creating complicated conditional statements and processing boolean logic.
Superscalar computers may contain multiple ALUs, allowing them to process several instructions simultaneously.^[49] Graphics processors and computers with SIMD and MIMD features often contain ALUs that can perform arithmetic on vectors and matrices.

Memory

Main article: Computer data storage

Magnetic core memory was the computer memory of choice throughout the 1960s, until it was replaced by semiconductor memory.

A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered “address” and can store a single number. The computer can be instructed to “put the number 123 into the cell numbered 1357” or to “add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595.” The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is the software's responsibility to give significance to what the memory sees as nothing but a series of numbers.
In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (2^8 = 256); either from 0 to 255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.
The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.
Computer main memory comes in two principal varieties: random-access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is preloaded with data and software that never changes, therefore the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.^[50]
In more sophisticated computers there may be one or more RAM cache memories, which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.

Input/output (I/O)

Main article: Input/output

Hard disk drives are common storage devices used with computers.

I/O is the means by which a computer exchanges information with the outside world.^[51] Devices that provide input or output to the computer are called peripherals.^[52] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.
I/O devices are often complex computers in their own right, with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics.^{[citation needed]} Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.

Multitasking

Main article: Computer multitasking

While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.^[53]
One means by which this is done is with a special signal called an interrupt, which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running “at the same time,” then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed “time-sharing” since each program is allocated a “slice” of time in turn.^[54]
Before the era of cheap computers, the principal use for multitasking was to allow many people to share the same computer.
Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly, in direct proportion to the number of programs it is running, but most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a “time slice” until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run simultaneously without unacceptable speed loss.

Multiprocessing

Main article: Multiprocessing

Cray designed many supercomputers that used multiprocessing heavily.

Some computers are designed to distribute their work across several CPUs in a multiprocessing configuration, a technique once employed only in large and powerful machines such as supercomputers, mainframe computers and servers. Multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result.
Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.^[55] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called “embarrassingly parallel” tasks.

Networking and the Internet

Main articles: Computer networking and Internet

Visualization of a portion of the routes on the Internet.

Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems such as Sabre.^[56]
In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. The effort was funded by ARPA (now DARPA), and the computer network that resulted was called the ARPANET.^[57] The technologies that made the Arpanet possible spread and evolved.
In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. “Wireless” networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.

Computer architecture paradigms

There are many types of computer architectures:

• Quantum computer vs Chemical computer
• Scalar processor vs Vector processor
• Non-Uniform Memory Access (NUMA) computers
• Register machine vs Stack machine
• Harvard architecture vs von Neumann architecture
• Cellular architecture

The quantum computer architecture holds the most promise to revolutionize computing.^[58]
Logic gates are a common abstraction which can apply to most of the above digital or analog paradigms.
The ability to store and execute lists of instructions called programs makes computers extremely versatile, distinguishing them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a minimum capability (being Turing-complete) is, in principle, capable of performing the same tasks that any other computer can perform. Therefore any type of computer (netbook, supercomputer, cellular automaton, etc.) is able to perform the same computational tasks, given enough time and storage capacity.

Misconceptions

Main articles: Human computer and Harvard Computers

Women as computers in NACA High Speed Flight Station "Computer Room"

A computer does not need to be electronic, nor even have a processor, nor RAM, nor even a hard disk. While popular usage of the word “computer” is synonymous with a personal electronic computer, the modern^[59] definition of a computer is literally “A device that computes, especially a programmable [usually] electronic machine that performs high-speed mathematical or logical operations or that assembles, stores, correlates, or otherwise processes information.”^[60] Any device which processes information qualifies as a computer, especially if the processing is purposeful.

Required technology

Main article: Unconventional computing

Historically, computers evolved from mechanical computers and eventually from vacuum tubes to transistors. However, conceptually computational systems as flexible as a personal computer can be built out of almost anything. For example, a computer can be made out of billiard balls (billiard ball computer); an often quoted example.^{[citation needed]} More realistically, modern computers are made out of transistors made of photolithographed semiconductors.
There is active research to make computers out of many promising new types of technology, such as optical computers, DNA computers, neural computers, and quantum computers. Most computers are universal, and are able to calculate any computable function, and are limited only by their memory capacity and operating speed. However different designs of computers can give very different performance for particular problems; for example quantum computers can potentially break some modern encryption algorithms (by quantum factoring) very quickly.

Further topics

• Glossary of computers

Artificial intelligence

A computer will solve problems in exactly the way it is programmed to, without regard to efficiency, alternative solutions, possible shortcuts, or possible errors in the code. Computer programs that learn and adapt are part of the emerging field of artificial intelligence and machine learning.

Hardware

Main articles: Computer hardware and Personal computer hardware

The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.

History of computing hardware

Main article: History of computing hardware

First generation (mechanical/electromechanical)	Calculators	Pascal's calculator, Arithmometer, Difference engine
	Programmable devices	Jacquard loom, Analytical engine, Harvard Mark I, Z3
Second generation (vacuum tubes)	Calculators	Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120
	Programmable devices	Colossus, ENIAC, Manchester Small-Scale Experimental Machine, EDSAC, Manchester Mark 1, Ferranti Pegasus, Ferranti Mercury, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22
Third generation (discrete transistors and SSI, MSI, LSI integrated circuits)	Mainframes	IBM 7090, IBM 7080, IBM System/360, BUNCH
	Minicomputer	PDP-8, PDP-11, IBM System/32, IBM System/36
Fourth generation (VLSI integrated circuits)	Minicomputer	VAX, IBM System i
	4-bit microcomputer	Intel 4004, Intel 4040
	8-bit microcomputer	Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80
	16-bit microcomputer	Intel 8088, Zilog Z8000, WDC 65816/65802
	32-bit microcomputer	Intel 80386, Pentium, Motorola 68000, ARM architecture
	64-bit microcomputer[61]	Alpha, MIPS, PA-RISC, PowerPC, SPARC, x86-64
	Embedded computer	Intel 8048, Intel 8051
	Personal computer	Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet PC, Wearable computer
Theoretical/experimental	Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics based computer

Other hardware topics

Peripheral device (input/output)	Input	Mouse, keyboard, joystick, image scanner, webcam, graphics tablet, microphone
	Output	Monitor, printer, loudspeaker
	Both	Floppy disk drive, hard disk drive, optical disc drive, teleprinter
Computer busses	Short range	RS-232, SCSI, PCI, USB
	Long range (computer networking)	Ethernet, ATM, FDDI

Software

Main article: Computer software

Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified (such as BIOS ROM in an IBM PC compatible), it is sometimes called “firmware.”

Operating system	Unix and BSD	UNIX System V, IBM AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systems
	GNU/Linux	List of Linux distributions, Comparison of Linux distributions
	Microsoft Windows	Windows 95, Windows 98, Windows NT, Windows 2000, Windows Me, Windows XP, Windows Vista, Windows 7, Windows 8
	DOS	86-DOS (QDOS), IBM PC DOS, MS-DOS, DR-DOS, FreeDOS
	Mac OS	Mac OS classic, Mac OS X
	Embedded and real-time	List of embedded operating systems
	Experimental	Amoeba, Oberon/Bluebottle, Plan 9 from Bell Labs
Library	Multimedia	DirectX, OpenGL, OpenAL
	Programming library	C standard library, Standard Template Library
Data	Protocol	TCP/IP, Kermit, FTP, HTTP, SMTP
	File format	HTML, XML, JPEG, MPEG, PNG
User interface	Graphical user interface (WIMP)	Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM, Aqua
	Text-based user interface	Command-line interface, Text user interface
Application	Office suite	Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting software
	Internet Access	Browser, E-mail client, Web server, Mail transfer agent, Instant messaging
	Design and manufacturing	Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain management
	Graphics	Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processing
	Audio	Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer music
	Software engineering	Compiler, Assembler, Interpreter, Debugger, Text editor, Integrated development environment, Software performance analysis, Revision control, Software configuration management
	Educational	Edutainment, Educational game, Serious game, Flight simulator
	Games	Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fiction
	Misc	Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems, File manager

Languages

There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.

Programming languages

Lists of programming languages	Timeline of programming languages, List of programming languages by category, Generational list of programming languages, List of programming languages, Non-English-based programming languages
Commonly used assembly languages	ARM, MIPS, x86
Commonly used high-level programming languages	Ada, BASIC, C, C++, C#, COBOL, Fortran, Java, Lisp, Pascal, Object Pascal
Commonly used scripting languages	Bourne script, JavaScript, Python, Ruby, PHP, Perl

Professions and organizations

As the use of computers has spread throughout society, there are an increasing number of careers involving computers.

Computer-related professions

Hardware-related	Electrical engineering, Electronic engineering, Computer engineering, Telecommunications engineering, Optical engineering, Nanoengineering
Software-related	Computer science, Computer engineering, Desktop publishing, Human–computer interaction, Information technology, Information systems, Computational science, Software engineering, Video game industry, Web design

The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature.

Organizations

Standards groups	ANSI, IEC, IEEE, IETF, ISO, W3C
Professional societies	ACM, AIS, IET, IFIP, BCS
Free/open source software groups	Free Software Foundation, Mozilla Foundation, Apache Software Foundation

 

the best COMPUTER TIPS AND TRICKS 20 amazing windows xp tricks

Windows XP Customisation

1. Remove the Recycle Bin
If you prefer to work with a completely clear desktop, you can hide the Recycle Bin with a little Registry hack. You can still use the [Shift] + [Delete] shortcut to access the Bin when you need it.
Choose 'Start > Run' and type 'Regedit' in the 'Open' bar. Click 'OK'. Now browse to: HKEY_ LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Current Version\Explorer\HideDesktop Icons\NewStartPanel. Create a new DWORD value and name it: '{645FF040-5081-101B-9F08-00AA002F954E}'
Double-click this and change its value to '1'. Quit Registry Editor, then right-click an empty space somewhere on your desktop and choose 'Refresh'. The Recycle Bin icon will magically disappear from the desktop. You can get it back again at any time by changing the value back to '0'.
2. Make folders stand out

When you're navigating your hard drive you can spend a lot of time looking at folders, so it's a good idea to customise them to suit your taste. Open the Folder Options control panel.
Here you can choose whether to show common task links to the left of folder windows, as well as the type of files you'd like displayed. You can change the icon or picture used to represent a folder (see tip 5), but you can also add a background image or colour to folders.
You could do this the hard way - by manually editing configuration files - but a better and easier way is to use a third-party program that can do the hard work for you. Windowpaper XP is that tool. Once installed, just select your chosen image, click 'Change Image' and select the image you want to use.
Note that you can't stretch or centre your chosen image - if it's smaller than the window in question it will tile, so bear that in mind when choosing your image. If the image is too vibrant, consider creating a copy in your image editor, then increasing the brightness and lowering the contrast to produce a washed-out look that won't distract you when browsing the folder.
3. Organise your applications

On any new Windows XP installation, it's a good idea to stack the Quick Launch toolbar on top of a double-decked taskbar so that everything you use is close at hand. You can then add shortcuts for all of your regularly used applications to the Quick Launch toolbar, as well as shortcuts to My Computer and your My Documents folder.
4. Create your own theme for Windows XP

Given that it's so important, and so easy to change, you'd have thought that Microsoft might have included more than two themes with Windows XP. Fortunately, it's easy to change the existing ones.
To change themes or colours, you'll need to get into the Display Properties. To do this, go to the Start menu and select 'Settings > Control Panel', then in the Control Panel select 'Display'.
Click the Appearance tab at the top of the dialog. You'll see that you can manually go in and change the colour of every menu, piece of text, dialog box and so on. If you don't like the default colours in the colour palette, click 'Advanced', then click the colour square, select 'Other' and you can create your own colours using RGB or HSV values.
For easier re-selection of colours that you create manually, click the 'Add to Custom Colours' button once you've created a new colour you're happy with, and it will now be added to the User Palette.
Finally, click the 'Desktop' tab. Here you can select an image to use as a background picture for your desktop. You can either use a small repeating pattern that can be tiled to fill the desktop, or you can use a single larger picture that fills the entire screen. If the picture is too small for the screen, you can select the stretch option to ensure that it fits.
Click the 'Browse' button to select a picture file from your hard drive. Windows XP recognises BMP, GIF, JPG, JPEG, DIB and PNG picture formats, as well as HTM and HTML web page formats. If your image is in another format, such as TIFF, you'll need to convert it using your favourite image editing program.
Having customised your display, click the left-hand tab in the Display Properties dialog, and you'll see the Themes window appear. From here, you can select one of the defaults from the drop-down list. More importantly, you can save the current theme for future use.
5. Change your icons
If you're not happy with the icons used for some of your shortcuts, you can change them to something else that may be more obvious (or make your own, see tip 6 below) for that particular type of application. Right-click the shortcut, select 'Properties', and click 'Change Icon'. Now, use the 'Browse' button to choose a file to search for icons, make your selection, and click 'OK'.
6. Make custom icons

If you decide to make your own custom icons, there are a few things to be aware of. First, they come in different sizes according to where they are displayed, such as the desktop, the Start menu, Folders, Drives, and so on.
Icons are measured in pixels, and the three sizes used on Windows XP are 16 x 16, 32 x 32 and 48 x 48. Second, icons use a 32-bit palette, enabling you to use any colour that the eye can detect.
In the past, icons were either opaque (solid), or completely transparent, making them appear as sharp-edged cutouts on the screen. Now, they can gently fade into the background, and you can create subtle shadow effects.
Finally, the default Windows icons are packaged and encoded into the shell32.dll, and many program icons are similarly hard-coded. If you choose to replace these icons, you can either select any of the default icons, or you can add icons you've downloaded from the internet or created yourself in an image editor or icon creator. Individual icons have the ICO file extension, while icon groups have the ICL extension.
7. Remove text from icons
You can improve the general look of your PC's desktop by removing the names of shortcuts, leaving the icons to speak for themselves. If you try renaming a desktop shortcut to a single space, Windows XP won't let you.
However, you can force it to accept a space as the name by holding down [Alt] and typing 255 on the number pad. If you want multiple shortcuts to have blank names, you'll need to give each one a different number of spaces to avoid them having identical names.
8. Remove programs from the 'Open With' list
Stop programs appearing on the 'Open with' list when you're trying to open an unrecognised file.
Open Regedit and browse to HKEY_ CLASSES_ROOT\Applications, and you'll see a list of programs that are installed on your PC as subkeys in the left-hand pane. To remove an unwanted program from this list, select it and right-click in the right hand pane.
Choose 'New > String value'. Name it 'NoOpenWith'. Repeat for each application that you want to remove from this list.
9. Choose a new screensaver

Windows XP comes complete with a selection of screensavers, and it's easy to switch between them. Right-click the desktop and choose 'Properties > Screensaver'. There are plenty more screensavers available online too, although be careful when looking for them. There's plenty of research that indicates that 'free screensaver' is a search term most likely to lead you to malicious software.
10. Personalise your folders with images

Right-click inside a folder and select 'Customize This Folder...'. If you decide you'd like to use a picture to represent your chosen folder, when you use thumbnail view, the folder icon will display the picture you've chosen. For example, if the folder is a collection of family snaps, you might want to use a photo of your family. Alternatively, you can use the Change Icon option to give individual folders a unique, identifiable icon.
11. Edit your drive names

If you've split your hard drive into two or more partitions, renaming drives can make them easier to identify. Partitions enable you to store groups of data separately from each other on your computer - effectively like having multiple hard drives. Simply right-click a hard drive partition in My Computer, select Properties, and enter a new label.
12. Disable autorun for discs
Put a disc in your CD/DVD drive and you'll notice an appreciable lag as it spins up, even if you're not just about to use it. If you don't always need your CDs and DVDs to launch automatically when you insert them, the needless spinning up of the discs can slow your machine down.
You can disable CD autorun by modifying this registry key:
'HKEY_LOCAL_ MACHINE\SYSTEM\Current ControlSet\Services\Cdrom'. Double-click the 'AutoRun Dword' value and set it to '0'. Change it to '1' to restore it.
13. Add your own sound effects

You can configure your system so that it plays sounds to accompany various events, such as when dialogs appear, or when you make menu selections. Visit the Sounds section of the 'Sounds & Audio Devices' control panel to choose from a number of pre-configured schemes, or choose any selection of WAV files from your hard drive and create your own schemes. You can even have your favourite song play when your PC starts up.
14. Create a mute shortcut
You can make a custom shortcut that mutes and unmutes your PC's sound by downloading a small utility called Nircmd.
Download and extract the file contents to 'My Documents'. Next, right-click the desktop and choose 'New > Shortcut'. Enter the following for the shortcut location:
"C:\Documents and Settings\Owner\My Documents\nircmd\nircmd.exe" mutesysvolume 2.
Ensure that the path points to the location where you extracted the 'Nircmd.exe' file. Name the shortcut 'mute_ unmute'. Double-click it to mute your speakers and do so again to turn them back on.
15. Correct file sorting
By default, a file named '2.jpg' will be sorted after one called '20.jpg'. Many people work around this by starting single-digit numbers in file names with a leading zero, but you can change this behaviour by making a Registry edit.
Browse to the Registry key HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explore. Create a new DWORD value and name it 'NoStrCmpLogical'. Right click and modify its value to '1'.
16. Display shortcut keys
When you open a menu or My Computer window in XP, you can see what shortcut keys are available by pressing [Alt] once - underlined letters will appear, and pressing that letter will trigger the appropriate shortcut, whether it's ticking a box or selecting a button.
You can make these underlined letters appear automatically from the 'Appearance' tab under the 'Desktop' control panel. Click the 'Effects' button and remove the tick next to the box marked 'Hide underlined letters for keyboard navigation until I press the Alt key'. Click 'OK' twice.
17. Perform a complete redesign with these tools
If you want to go beyond the options in Windows XP itself you can try an overhaul using these customisation tools:

TweakUI: No discussion about personalising your PC would be complete without mentioning TweakUI - the indispensable Microsoft tool from the team behind Windows XP. There are so many small but important changes you can make to your system with this program, but by far the best way to find out about them is to download it and experiment.

Talisman Desktop: If you're interested in more extreme forms of computer personalisation, Talisman Desktop can completely transform the appearance of your desktop - even the default theme is something to behold, but there are plenty more available for you to choose from.

WindowBlinds: Next you should head over to Stardock, where you'll find even more desktop enhancements. One such example is WindowBlinds, which enables you to not only change the appearance of your windows, but also the way they act. It's one of the most powerful customisation tools, and you'll find plenty of other tools on offer too - the full set is available for £32/$50 as part of the Object Desktop suite.
18. Make Windows XP fun for your kids, Part 1

The first thing you should do before installing anything on your system is create a separate account for your kids. Open the User Accounts Control Panel, create a new account and select 'Limited' for the account type.
There are several ways of making your desktop child-friendly without installing extra software. First, get yourself a good wallpaper. Younger children can find a range of excellent wallpapers at the Cbeebies website. You could also take a look at the wallpapers from the National Geographic for older kids.
What about the icons? There are a couple of options here - older children will enjoy the Plou icons available in Stardock's IconPackager. Alternatively, another set of child-friendly icons can be found at WinCustomize.
19. Make Windows XP fun for your kids, Part 2

Since we're forgetting all concepts of taste in pursuit of an appealing children's desktop, why not swap the standard cursors too? You'll need CursorFX to use the really bright and colourful ones.
Once you've downloaded and installed the program, open the configuration window and click the CursorFX tab. You can select the different cursor sets from the Theme drop-down menu. To install a new theme select 'Browse' from the Theme drop-down menu. After a short pause while CursorFX renders the icons, you'll see your new set. Configure each cursor by clicking the Configure button and double-clicking an item in the main window. Save your modified set by clicking 'Save As'.
20. Make Windows XP fun for your kids, Part 3

You can really go to town on your desktop if you use a shell program. DesktopX is a great way of combining an enjoyable environment with access control. In Edit mode you can set up the desktop, and in User mode, you lock everything down.
You can import large pictures and use them as shortcuts to specific programs, and you can include sounds and animations too. The program comes with a couple of basic examples, such as a theme called Kids, which includes an embedded web browser and links to five sites. Your children can only access those sites, and they're unlikely to encounter anything dubious no matter how many external links they manage to follow.
Load DesktopX Builder by selecting 'Start > Programs > StarDock > Desktop Object > DesktopX Builder'. Load the 'Desktop Playground' theme if it isn't already. This mode enables you to customise the desktop in many ways - we'll add a web shortcut.
If you want to do some editing then right-click one of the frames and select 'Properties > States'. The 'Appearance' tab below should be selected. Click the 'Browse' button and select the PNG files, now click the 'Mouse Over' state and select the PNG file.