ABOUT light-emitting diode (LED)

A light-emitting diode (LED) is a semiconductor device that emits visible light when an electric current passes through it. The light is not particularly bright, but in most LEDs it is monochromatic, occurring at a single wavelength. The output from an LED can range from red (at a wavelength of approximately 700 nanometers) to blue-violet (about 400 nanometers). Some LEDs emit infrared (IR) energy (830 nanometers or longer); such a device is known as an infrared-emitting diode (IRED).

An LED or IRED consists of two elements of processed material called P-type semiconductors and N-type semiconductors. These two elements are placed in direct contact, forming a region called the P-N junction. In this respect, the LED or IRED resembles most other diode types, but there are important differences. The LED or IRED has a transparent package, allowing visible or IR energy to pass through. Also, the LED or IRED has a large PN-junction area whose shape is tailored to the application.

Benefits of LEDs and IREDs, compared with incandescent and fluorescent illuminating devices, include:

• Low power requirement: Most types can be operated with battery power supplies.
• High efficiency: Most of the power supplied to an LED or IRED is converted into radiation in the desired form, with minimal heat production.
• Long life: When properly installed, an LED or IRED can function for decades.

Typical applications include:

• Indicator lights: These can be two-state (i.e., on/off), bar-graph, or alphabetic-numeric readouts.
• LCD panel backlighting: Specialized white LEDs are used in flat-panel computer displays.
• Fiber optic data transmission: Ease of modulation allows wide communications bandwidth with minimal noise, resulting in high speed and accuracy.
• Remote control: Most home-entertainment "remotes" use IREDs to transmit data to the main unit.
• Optoisolator: Stages in an electronic system can be connected together without unwanted interaction.

Stacks and Queues

An array is a random access data structure, where each element can be accessed directly and in constant time. A typical illustration of random access is a book - each page of the book can be open independently of others. Random access is critical to many algorithms, for example binary search.
A linked list is a sequential access data structure, where each element can be accesed only in particular order. A typical illustration of sequential access is a roll of paper or tape - all prior material must be unrolled in order to get to data you want.
In this note we consider a subcase of sequential data structures, so-called limited access data sturctures.

Stacks

A stack is a container of objects that are inserted and removed according to the last-in first-out (LIFO) principle. In the pushdown stacks only two operations are allowed: push the item into the stack, and pop the item out of the stack. A stack is a limited access data structure - elements can be added and removed from the stack only at the top. push adds an item to the top of the stack, pop removes the item from the top. A helpful analogy is to think of a stack of books; you can remove only the top book, also you can add a new book on the top.A stack is a recursive data structure. Here is a structural definition of a Stack: Applications The simplest application of a stack is to reverse a word. You push a given word to stack - letter by letter - and then pop letters from the stack. Another application is an "undo" mechanism in text editors; this operation is accomplished by keeping all text changes in a stack. Backtracking. This is a process when you need to access the most recent data element in a series of elements. Think of a labyrinth or maze - how do you find a way from an entrance to an exit? Once you reach a dead end, you must backtrack. But backtrack to where? to the previous choice point. Therefore, at each choice point you store on a stack all possible choices. Then backtracking simply means popping a next choice from the stack. Language processing: space for parameters and local variables is created internally using a stack. compiler's syntax check for matching braces is implemented by using stack. support for recursion. Implementation In the standard library of classes, the data type stack is an adapter class, meaning that a stack is built on top of other data structures. The underlying structure for a stack could be an array, a vector, an ArrayList, a linked list, or any other collection. Regardless of the type of the underlying data structure, a Stack must implement the same functionality. This is achieved by providing a unique interface: public interface StackInterface<AnyType> { public void push(AnyType e); public AnyType pop(); public AnyType peek(); public boolean isEmpty(); } The following picture demonstrates the idea of implementation by composition. Another implementation requirement (in addition to the above interface) is that all stack operations must run in constant time O(1). Constant time means that there is some constant k such that an operation takes k nanoseconds of computational time regardless of the stack size. Array-based implementation   In an array-based implementation we maintain the following fields: an array A of a default size (≥ 1), the variable top that refers to the top element in the stack and the capacity that refers to the array size. The variable top changes from -1 to capacity - 1. We say that a stack is empty when top = -1, and the stack is full when top = capacity-1.In a fixed-size stack abstraction, the capacity stays unchanged, therefore when top reaches capacity, the stack object throws an exception. In a dynamic stack abstraction when top reaches capacity, we double up the stack size. Linked List-based implementation Linked List-based implementation provides the best (from the efficiency point of view) dynamic stack implementation. Queues A queue is a container of objects (a linear collection) that are inserted and removed according to the first-in first-out (FIFO) principle. An excellent example of a queue is a line of students in the food court of the UC. New additions to a line made to the back of the queue, while removal (or serving) happens in the front. In the queue only two operations are allowed enqueue and dequeue. Enqueue means to insert an item into the back of the queue, dequeue means removing the front item. The picture demonstrates the FIFO access.The difference between stacks and queues is in removing. In a stack we remove the item the most recently added; in a queue, we remove the item the least recently added. Implementation In the standard library of classes, the data type queue is an adapter class, meaning that a queue is built on top of other data structures. The underlying structure for a queue could be an array, a Vector, an ArrayList, a LinkedList, or any other collection. Regardless of the type of the underlying data structure, a queue must implement the same functionality. This is achieved by providing a unique interface. interface QueueInterface‹AnyType> { public boolean isEmpty(); public AnyType getFront(); public AnyType dequeue(); public void enqueue(AnyType e); public void clear(); } Each of the above basic operations must run at constant time O(1). The following picture demonstrates the idea of implementation by composition. Applications The simplest two search techniques are known as Depth-First Search(DFS) and Breadth-First Search (BFS). These two searches are described by looking at how the search tree (representing all the possible paths from the start) will be traversed. Deapth-First Search with a Stack In depth-first search we go down a path until we get to a dead end; then we backtrack or back up (by popping a stack) to get an alternative path. Create a stack Create a new choice point Push the choice point onto the stack while (not found and stack is not empty) Pop the stack Find all possible choices after the last one tried Push these choices onto the stack Return Breadth-First Search with a Queue In breadth-first search we explore all the nearest possibilities by finding all possible successors and enqueue them to a queue. Create a queue Create a new choice point Enqueue the choice point onto the queue while (not found and queue is not empty) Dequeue the queue Find all possible choices after the last one tried Enqueue these choices onto the queue Return We will see more on search techniques later in the course. Arithmetic Expression Evaluation An important application of stacks is in parsing. For example, a compiler must parse arithmetic expressions written using infix notation: 1 + ((2 + 3) * 4 + 5)*6 We break the problem of parsing infix expressions into two stages. First, we convert from infix to a different representation called postfix. Then we parse the postfix expression, which is a somewhat easier problem than directly parsing infix. Converting from Infix to Postfix. Typically, we deal with expressions in infix notation 2 + 5 where the operators (e.g. +, *) are written between the operands (e.q, 2 and 5). Writing the operators after the operands gives a postfix expression 2 and 5 are called operands, and the '+' is operator. The above arithmetic expression is called infix, since the operator is in between operands. The expression 2 5 + Writing the operators before the operands gives a prefix expression +2 5 Suppose you want to compute the cost of your shopping trip. To do so, you add a list of numbers and multiply them by the local sales tax (7.25%): 70 + 150 * 1.0725 Depending on the calculator, the answer would be either 235.95 or 230.875. To avoid this confusion we shall use a postfix notation 70 150 + 1.0725 * Postfix has the nice property that parentheses are unnecessary. Now, we describe how to convert from infix to postfix. Read in the tokens one at a time If a token is an integer, write it into the output If a token is an operator, push it to the stack, if the stack is empty. If the stack is not empty, you pop entries with higher or equal priority and only then you push that token to the stack. If a token is a left parentheses '(', push it to the stack If a token is a right parentheses ')', you pop entries until you meet '('. When you finish reading the string, you pop up all tokens which are left there. Arithmetic precedence is in increasing order: '+', '-', '*', '/'; Example. Suppose we have an infix expression:2+(4+3*2+1)/3. We read the string by characters. '2' - send to the output. '+' - push on the stack. '(' - push on the stack. '4' - send to the output. '+' - push on the stack. '3' - send to the output. '*' - push on the stack. '2' - send to the output. Evaluating a Postfix Expression. We describe how to parse and evaluate a postfix expression. We read the tokens in one at a time. If it is an integer, push it on the stack If it is a binary operator, pop the top two elements from the stack, apply the operator, and push the result back on the stack. Consider the following postfix expression 5 9 3 + 4 2 * * 7 + * Here is a chain of operations Stack Operations Output -------------------------------------- push(5); 5 push(9); 5 9 push(3); 5 9 3 push(pop() + pop()) 5 12 push(4); 5 12 4 push(2); 5 12 4 2 push(pop() * pop()) 5 12 8 push(pop() * pop()) 5 96 push(7) 5 96 7 push(pop() + pop()) 5 103 push(pop() * pop()) 515 Note, that division is not a commutative operation, so 2/3 is not the same as 3/2.

GRAPHICS CARDS

A Graphics Card is a piece of computer hardware that produces the image you see on a monitor.

The Graphics Card is responsible for rendering an image to your monitor, it does this by converting data into a signal your monitor can understand.

The better your graphics card the better, and smoother an image can be produced. This is naturally very important for gamers and video editors.

The images you see on your monitorare made of tiny dots called pixels. At most common resolution settings, a screen displays over a million pixels, and the computer has to decide what to do with every one in order to create an image. To do this, it needs a translator -- something to take binary data from the CPU and turn it into a picture you can see. Unless a computer has graphics capability built into themotherboard, that translation takes place on the graphics card.

A graphics card's job is complex, but its principles and components are easy to understand. In this article, we will look at the basic parts of a video card and what they do. We'll also examine the factors that work together to make a fast, efficient graphics card..

SOUND CARDS(history,functions,uses,types,etc.)

A sound card (also known as an audio card) is an internal computer expansion card that facilitates economical input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware inside the PC. Typical uses of sound cards include providing the audio component for multimedia applications such as music composition, editing video or audio, presentation, education and entertainment (games) and video projection.

Sound functionality can also be integrated onto the motherboard, using basically the same components as a plug-in card. The best plug-in cards, which use better and more expensive components, can achieve higher quality than integrated sound. The integrated sound system is often still referred to as a "sound card".

Color		Function	Connector	symbol
	Pink	Analog microphone audio input.	3.5 mmminijack	A microphone
	Light blue	Analog line level audio input.	3.5 mmminijack	An arrow going into a circle
	Lime green	Analog line level audio output for the main stereo signal (front speakers or headphones).	3.5 mmminijack	Arrow going out one side of a circle into a wave
	Orange	Analog line level audio output for center channel speaker and subwoofer.	3.5 mmminijack
	Black	Analog line level audio output for surround speakers, typically rear stereo.	3.5 mmminijack
	Silver/Grey	Analog line level audio output for surround optional side channels.	3.5 mmminijack
	Brown/Dark	Analog line level audio output for a special panning, 'Right-to-left speaker'.	3.5 mmminijack
	Gold/Grey	Game port / MIDI	15 pin D	Arrow going out both sides into waves

The main function of a sound card is to play audio, usually music, with varying formats (monophonic, stereophonic, various multiple speaker setups) and degrees of control. The source may be a CD or DVD, a file, streamed audio, or any external source connected to a sound card input.

Audio may be recorded. Sometimes sound card hardware and drivers do not support recording a source that is being played.

A card can also be used, in conjunction with software, to generate arbitrary wave forms, acting as an audio-frequency function generator. Free and commercial software is available for this purpose.there are also online services that generate audio files for any desired wave forms, playable through a sound card.

A card can be used, again in conjunction with free or commercial software, to analyse input waveforms. For example, a very-low-distortion sinewave oscillator can be used as input to equipment under test; the output is sent to a sound card's line input and run through Fourier transform software to find the amplitude of each harmonic of the added distortion. Alternatively, a less pure signal source may be used, with circuitry to subtract the input from the output, attenuated and phase-corrected; the result is distortion and noise only, which can be analysed.

There are programs which allow a sound card to be used as an audio-frequency oscilloscope.

For all measurement purposes a sound card must be chosen with good audio properties. It must itself contribute as little distortion and noise as possible, and attention must be paid to bandwidth and sampling. A typical integrated sound card, the Realtek ALC887, according to its data sheet has distortion of about 80dB below the fundamental; cards are available with distortion better than -100dB.

Driver architecture

To use a sound card, the operating system (OS) typically requires a specific device driver, a low-level program that handles the data connections between the physical hardware and the operating system. Some operating systems include the drivers for many cards; for cards not so supported, drivers are supplied with the card, or available for download.

•DOS programs for the IBM PC often had to use universal middleware driver libraries (such as the HMI Sound Operating System, the Miles Audio Interface Libraries (AIL), the Miles Sound System etc.) which had drivers for most common sound cards, since DOS itself had no real concept of a sound card. Some card manufacturers provided (sometimes inefficient) middleware TSR-based drivers for their products. Often the driver is a Sound Blaster and AdLib emulator designed to allow their products to emulate a Sound Blaster and AdLib, and to allow games that could only use SoundBlaster or AdLib sound to work with the card. Finally, some programs simply had driver/middleware source code incorporated into the program itself for the sound cards that were supported.

•Microsoft Windows uses drivers generally written by the sound card manufacturers. Many device manufacturers supply the drivers on their own discs or to Microsoft for inclusion on Windows installation disc. Sometimes drivers are also supplied by the individual vendors for download and installation. Bug fixes and other improvements are likely to be available faster via downloading, since CDs cannot be updated as frequently as a web or FTP site. USB audio device class support is present from Windows 98 SE onwards. Since Microsoft's Universal Audio Architecture (UAA) initiative which supports the HD Audio, FireWire andUSB audio device class standards, a universal class driver by Microsoft can be used. The driver is included with Windows Vista. For Windows XP, Windows 2000or Windows Server 2003, the driver can be obtained by contacting Microsoft support.[15] Almost all manufacturer-supplied drivers for such devices also include this class driver.

•A number of versions of UNIX make use of the portable Open Sound System (OSS). Drivers are seldom produced by the card manufacturer.

•Most present day Linux distributions make use of the Advanced Linux Sound Architecture (ALSA). Up until Linux kernel 2.4, OSS was the standard sound architecture for Linux, although ALSA can be downloaded, compiled and installed separately for kernels 2.2 or higher. But from kernel 2.5 onwards, ALSA was integrated into the kernel and the OSS native drivers were deprecated. Backwards compatibility with OSS-based software is maintained, however, by the use of the ALSA-OSS compatibility API and the OSS-emulation kernel modules.

•Mockingboard support on the Apple II is usually incorporated into the programs itself as many programs for the Apple II boot directly from disk. However a TSR is shipped on a disk that adds instructions to Apple Basic so users can create programs that use the card, provided that the TSR is loaded first

MONITORS

A monitor or a display is an electronic visual display for computers. The monitor comprises the display device, circuitry and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors used a cathode ray tube (CRT) about as deep as the screen size.

Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratioof televisions, and then computer monitors, has also changed from 4:3 to 16:9.

History Early electronic computers were fitted with a panel of light bulbs where the state of each particular bulb would indicate the on/off state of a particular registerbit inside the computer. This allowed the engineers operating the computer to monitor the internal state of the machine, so this panel of lights came to be known as the 'monitor'. As early monitors were only capable of displaying a very limited amount of information, and were very transient, they were rarely considered for programme output. Instead, a line printer was the primary output device, while the monitor was limited to keeping track of the programme's operation.

As technology developed it was realized that the output of a CRT display was more flexible than a panel of light bulbs and eventually, by giving control of what was displayed to the programme itself, the monitor itself became a powerful output device in its own right.

HISTORY

The first computer monitors used cathode ray tubes (CRTs). Prior to the advent of home computers in the late 1970s, it was common for a video display terminal(VDT) using a CRT to be physically integrated with a keyboard and other components of the system in a single large chassis. The display was monochrome and far less sharp and detailed than on a modern flat-panel monitor, necessitating the use of relatively large text and severely limiting the amount of information that could be displayed at one time. High-resolution CRT displays were developed for specialized military, industrial and scientific applications but they were far too costly for general use.

Some of the earliest home computers (such as the TRS-80 and Commodore PET) were limited to monochrome CRT displays, but color display capability was already a standard feature of the pioneering Apple II, introduced in 1977, and the specialty of the more graphically sophisticated Atari 800, introduced in 1979. Either computer could be connected to the antenna terminals of an ordinary color TV set or used with a purpose-made CRT color monitor for optimum resolution and color quality. Lagging several years behind, in 1981 IBM introduced the Color Graphics Adapter, which could display four colors with a resolution of 320 x 200 pixels, or it could produce 640 x 200 pixels with two colors. In 1984 IBM introduced the Enhanced Graphics Adapter which was capable of producing 16 colors and had a resolution of 640 x 350.

By the end of the 1980s color CRT monitors that could clearly display 1024 x 768 pixels were widely available and increasingly affordable. During the following decade maximum display resolutions gradually increased and prices continued to fall. CRT technology remained dominant in the PC monitor market into the new millennium partly because it was cheaper to produce and offered viewing angles close to 180 degrees.[2] CRTs still offer some image quality advantages over LCD displays but improvements to the latter have made them much less obvious. The dynamic range of early LCD panels was very poor, and although text and other motionless graphics were sharper than on a CRT, an LCD characteristic known as pixel lag caused moving graphics to appear noticeably smeared and blurry.

Liquid crystal display

There are multiple technologies that have been used to implement liquid crystal displays (LCD). Throughout the 1990s, the primary use of LCD technology as computer monitors was in laptops where the lower power consumption, lighter weight, and smaller physical size of LCDs justified the higher price versus a CRT. Commonly, the same laptop would be offered with an assortment of display options at increasing price points: (active or passive) monochrome, passive color, or active matrix color (TFT). As volume and manufacturing capability have improved, the monochrome and passive color technologies were dropped from most product lines.

TFT-LCD is a variant of LCD which is now the dominant technology used for computer monitors.

The first standalone LCD displays appeared in the mid-1990s selling for high prices. As prices declined over a period of years they became more popular, and by 1997 were competing with CRT monitors. Among the first desktop LCD computer monitors was the Eizo L66 in the mid-1990s, the Apple Studio Display in 1998, and the Apple Cinema Display in 1999. In 2003, TFT-LCDs outsold CRTs for the first time, becoming the primary technology used for computer monitors. The main advantages of LCDs over CRT displays are that LCDs consume less power, take up much less space, and are considerably lighter. The now common active matrix TFT-LCD technology also has less flickering than CRTs, which reduces eye strain.On the other hand, CRT monitors have superior contrast, have superior response time, are able to use multiple screen resolutions natively, and there is no discernible flicker if the refresh rate is set to a sufficiently high value. LCD monitors have now very high temporal accuracy and can be used for vision research.

HARD DISK

A hard disk drive (HDD) is a data storage device used for storing and retrieving digital information using rapidly rotating disks (platters) coated with magnetic material. An HDD retains its data even when powered off. Data is read in a random-access manner, meaning individual blocks of data can be stored or retrieved in any order rather than sequentially. An HDD consists of one or more rigid ("hard") rapidly rotating disks (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.

Introduced by IBM in 1956, HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers andpersonal computers. More than 200 companies have produced HDD units, though most current units are manufactured by Seagate, Toshiba and Western Digital. Worldwide disk storage revenues were US $32 billion in 2013, down 3% from 2012.

The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixescorresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes). Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Performance is specified by the time required to move the heads to a track or cylinder (average access time) plus the time it takes for the desired sector to move under the head (average latency, which is a function of the physical rotational speed in revolutions per minute), and finally the speed at which the data is transmitted (data rate).

The two most common form factors for modern HDDs are 3.5-inch in desktop computers and 2.5-inch in laptops. HDDs are connected to systems by standard interface cables such as SATA (Serial ATA), USB or SAS (Serial attached SCSI) cables.

As of 2015, the primary competing technology for secondary storage is flash memory in the form of solid-state drives(SSDs). HDDs are the dominant medium for secondary storage due to advantages in price per unit of storage and recording capacity. However, SSDs are replacing HDDs where speed, power consumption and durability are more important considerations.

CMOS BATTERY(use,working,history,replacement,etc)

Nonvolatile BIOS memory refers to a small memory on PC motherboards that is used to store BIOS settings. It was traditionally called CMOS RAM because it used a volatile, low-power complementary metal-oxide-semiconductor (CMOS) SRAM (such as theMotorola MC146818 or similar) powered by a small battery when system power was off (called the CMOS battery).
The term remains in wide use but it has grown into a misnomer: nonvolatile storage in contemporary computers is often in EEPROM or flash memory (like the BIOS code itself); the remaining usage for the battery is then to keep the real-time clock (RTC) going. The typical NVRAM capacity is 512 bytes, which is generally sufficient for all BIOS settings. The CMOS RAM and the real-time clock have been integrated as a part of thesouthbridge chipset and it may not be a standalone chip on modern motherboards.

CMOS battery

Type CR2032 button cell, most common CMOS battery.
The memory battery (aka motherboard, CMOS, real-time clock-RTC, clock battery) is generally a CR2032 lithium coin cell. These cells last two to ten years, depending on the type of motherboard, ambient temperature and the length of time that the system is powered off, while other common cell types can last significantly longer or shorter periods, such as the CR2016which will generally last about 40% less than CR2032. Higher temperatures and longer power-off time will shorten cell life. When replacing the cell, the system time and CMOS BIOS settings may revert to default values. This may be avoided by replacing the cell with the power supply master switch on. On ATX motherboards, this will supply 5V power to the motherboard even if it is apparently "switched off", and keep the CMOS memory energized. In general one should not work on a computer that is powered.
Some computer designs have used non-button cell batteries, such as the cylindrical "1/2 AA" used in the Power Mac G4 as well as some older IBM PC compatibles, or a 3-cell NiCd CMOS battery that looks like a "barrel" (common in Amigas and older IBM PC compatibles), which serves the same purpose.
With (non-accesible close) computers you may need to disconnect cables, remove drives, or remove other parts of the computer to get full access to the CMOS battery.
First-4-screws replacement
First-4-screws CMOS battery replacement means that you only need open the first laptop 4 screw to replace the CMOS battery. Usually the keyboard does not need to be moved.
Extension cord[
A cable terminated with a 2 pin Molex connector plug can be used as an electrical extension cord, for an easy access to replace CMOS battery (to put the battery in the more easily accesible place).

Rechargeable CMOS battery or capacitors

Asus Eee PC series Models 1005ha 1005hab 1008ha and others use Varta ML1220 or equivalent Maxell, Sanyo andPanasonic ML1220 Lithium Ion coin cell rechargeable batteries, terminated with a 2 pin Molex connector plug.

Capacitors

Rather than using a battery, heavy duty capacitors can be used as an alternative. They would be connected where the original NiCd / NiMH battery goes.

Resetting the CMOS settings

To access the BIOS setup when the machine fails to operate, occasionally a drastic move is required. In older computers with battery-backed RAM, removal of the battery and short circuiting the battery input terminals for a while did the job; in some more modern machines this move only resets the RTC. Some motherboards offer a CMOS-reset jumper or a reset button. In yet other cases, the EEPROM chip has to be desoldered and the data in it manually edited using a programmer. Sometimes it is enough to ground the CLK or DTA line of the I²C bus of the EEPROM at the right moment during boot, this requires some precise soldering on SMD parts. If the machine lets one boot but does not want to let the user into the BIOS setup, one possible recovery is to deliberately "damage" the CMOS checksum by doing direct port writes using DOSdebug.exe, corrupting some bytes of the checksum-protected area of the CMOS RAM; at the next boot, the computer typically resets its setting to factory defaults.