Memory > RAM

RAM digunakan untuk menyimpan data dan instruksi dari software yang sedang dioperasikan oleh komputer.

Jenis RAM terdiri dari:

• SDRAM (Statis RAM)
• DRAM (Dinamic RAM)

DRAM disebut memori dinamis karena harus direcharge (diperbaharui muatan listriknya) secara periodik karena pengaruh sifat kebocoran muatan yang dimiliki oleh kapasitor yang dipakai untuk membuat sel-sel memori dari DRAM. Kelebihan DRAM adalah lebih murah dan lebih mudah rangkaiannya sehingga satu chip DRAM dapat memuat sel bit data jauh lebih besar dari SRAM.

SRAM tidak perlu direcharge seperti DRAM karena memakai desain dengan transistor. Kelebihan SRAM adalah akses data lebih cepat dari DRAM dan lebih stabil menyimpan data.

SDRAM digunakan pada cache memori internal (L1) dan memori eksternal (L2) dari prosesor. Sedangkan DRAM dipakai pada chip penyusun modul memori yang terpasang di motherboard.

DRAM dapat dikatagorikan menurut metode akses datanya atas:

• FPM (Fast Page Mode)
• EDO (Extended Data Out)
• BEDO (Burst EDO)
• SDRAM (Synchronous DRAM)
• RDRAM (Rambus DRAM)
• DDR SDRAM (Double Data Rate SDRAM)

Chip DRAM dirangkai dalam modul memori kemudian dipasang pada slot memori di motherboard. Jenis modul memori DRAM terdiri dari:

• SIMM (Single Inline Memory Module), dengan jenis 30pin (Data 8 bit + 4 bit parity optional)
• DIMM (Dual Inline Memori Module), dengan jenis 168 pin.

Motherboard

Motherboard atau main board adalah papan sirkuit terbesar pada komputer dan merupakan "Badan" yang menghubungkan seluruh unit pada sistem komputer. Komponen pokok pada motherboard terdiri dari:

• Socket/Slot processor
• Chipset (Northbridge dan Southbridge)
• Super I/O Chip
• ROM BIOS
• Socket memory (SIMM/DIMM/RIMM)
• Slot Bus (Jenis ISA/PCI/AGP)
• Voltage Regulator
• Baterry CMOS

Contoh Diagram Motherboard salah satu produk Intel:

Motherboard dibedakan menurut tipe processor yang didukung dan form factor (bentuk dan ukuran) dari motherboard. Dari socket/slot processor yang terpasang dapat diketahui jenis processor yang sesuai untuk motherboard tersebut.

Form factor motherboard terdiri dari jenis:

• Baby AT
• Full Size AT
• LPX
• ATX
• Micro ATX
• NLX
• WTX
• Flex ATX

Processor

Processor atau CPU (Central Processing Unit) merupakan otak dari komputer yang melakukan pemerosesan dan operasi perhitungan dan logika terhadap instruksi program yang diberikan ke komputer.

Chip processor dibuat dari keping silikon murni sebesar kuku jari berisi rangkaian terintegrasi dari ribuan hingga jutaan transistor yang mengimplementasikan fungsi dari processor. Rangkaian processor dihubungkan dengan kaki-kaki yang terdapat di bawah chip untuk jalur komunikasi sinyal masuk dan keluar dari rangkaian.

Kinerja dari setiap jenis processor bervariasi dan dipengaruhi oleh faktor-faktor berikut:

• Kecepatan Clock
• Lebar register/data bus internal
• Lebar data bus eksternal
• Kapasitas cache memori (L1 dan L2)

Pengantar Dasar Komputer

Komputer adalah alat yang dipakai untuk mengolah data menurut prosedur yang telah dirumuskan. Kata computer semula dipergunakan untuk menggambarkan orang yang perkerjaannya melakukan perhitungan aritmatika, dengan atau tanpa alat bantu, tetapi arti kata ini kemudian dipindahkan kepada mesin itu sendiri. Asal mulanya, pengolahan informasi hampir eksklusif berhubungan dengan masalah aritmatika, tetapi komputer modern dipakai untuk banyak tugas yang tidak berhubungan dengan matematika. (wikipedia)

bagian dasar komputer :

1> input device

2> central processing unit (CPU)

3> output device

4> external memory

1>input device

Input device bisa diartikan sebagai peralatan yang berfungsi untuk memasukkan data ke-dalam komputer. Jenis input device yang dimiliki oleh komputer contoh nya, keyboard, mouse, light-pen, scanner,finger print, dll

2>central proocessing unit (cpu)

Bagian ini berfungsi sebagai pemegang kendali dari jalannya kegiatan komputer, dan dikarenakan itu, CPU juga disebut sebagai otak dari komputer. Selain dari pada itu, CPU juga berfungsi sebagai tempat untuk melakukan pelbagai pengolahan data. Pekerjaan pengolahan data diantaranya: mencatat, melihat, membaca, membandingkan, menghitung, mengingat, mengurutkan maupun membandingkan.

Dalam bekerja, fungsi dari CPU terbagi menjadi :

- Internal Memory/Main Memory, berfungsi untuk me-nyimpan data dan program.

- ALU (Arithmatic Logical Unit), untuk melaksanakan perbagai macam perhitungan.

- Control Unit, bertugas untuk mengatur seluruh operasi komputer

3>output device

Output device bisa diartikan sebagai peralatan yang berfungsi untuk mengeluarkan hasil pemrosesan ataupun pengolahan data yang berasal dari CPU kedalam suatu media yang dapat dibaca oleh manusia ataupun dapat digunakan untuk penyimpanan data hasil proses. Jenis output device yang dimiliki oleh komputer printer, monitor,plotter,voiceres, dll

4> external memory

External memory bisa diartikan sebagai memory yang berada diluar CPU. Juga disebut sebagai Secondary Storage ataupun Backing Storage ataupun Memory Cadangan yang berfungsi untuk menyimpan data dan program. Data dan program yang tersimpan didalam external memory, agar bisa berfungsi data dan program tersebut harus dipindahkan terlebih dahulu kedalam internal memory. Jenis external memory antara lain disket, hard-disk, tape, cd, flash disk, card dll

Sedangkan yang disebut dengan program adalah kumpulan instruksi atau perintah terperinci yang sudah dipersiapkan supaya komputer dapat melakukan fungsinya dengan cara yang sudah tertentu. program juga merupakan suatu interface antara manusia dengan komputer.

Bit = satuan paling dasar dalam jaringan “organ” komputer, atau bagian dalam komputer. Pada dasarnya bilangan bit merupakan perwakilan aliran listrik, yakni hanya ada 2 saja yaitu 1 dan 0, yang bisa disebut 1 = ada listrik dan 0 = tidak ada listrik.

Byte = nah, ini baru satuan paling dasar komputer. 1 byte terdiri dari 8 bit. Oleh karena itu 1 byte bisa mewakili angka sampai 255, (kalau dijelaskan panjang, karena hubungan ama matematika, singkatnya bilangan 15 desimal = 1111 dalam bilangan bit). byte bisa juga mewakili 1 karakter komputer.

file = Arsip yang disimpan dalam suatu media, yang terdiri dari kumpulan karakter, dan didokumentasikan dalam bentuk data digital oleh komputer.

field = Di dalam database diartikan sebagai identitas spesifik dari sebuah objek. Misal objeknya mobil, field warnanya biru, field bahan bakar solar, dst.

1. Sistem Operasi, merupakan perangkat lunak yang mengoperasikan komputer serta menyediakan antarmuka dengan perangkat lunak lain atau dengan pengguna.

Contoh sistem operasi : MS DOS, MS Windows (dengan berbagai generasi),

Macintosh, OS/2, UNIX (dengan berbagai versi), LINUX (dengan berbagai

distribusi), NetWare, dll

2. Program Utilitas, merupakan program khusus yang berfungsi sebagai perangkat pemeliharaan komputer, seperti anti virus, partisi hardisk, manajemen hardisk, dll. Contoh produk program utilitas : Norton Utilities, PartitionMagic, McAfee, dll

3. Program Aplikasi, merupakan program yang dikembangkan untuk memenuhi kebutuhan yang spesifik. Contoh : aplikasi akuntansi, aplikasi perbankan, aplikasi manufaktur, dll

Keuntungan PC (Personal Computer) :

1. Tidak memakan tempat, karena bentuk nya tidak besar (seperti mainframe)

2. Bisa digunakan sebagai client atau server. Dan bisa juga standalone

3. General Purpose, merupakan komputer yang dikembangkan untuk kebutuhan umum.

Copy : menduplikat file asli tanpa harus menghapuss file asli tersebut ditempat(folder) aslinya

Cut : memindahkan file asli dari tempat(folder) awal ketempat(folder) yang diinginkan. File asli ditempat(folder) awal akan terhapus.

from : http://nugroz.wordpress.com

What is a Network

The word network can be used to describe a very large and complicated set of equipment. In its most accurate and simplest definition a network refers to the cables and electronic components that amplify the signals going through the cables. The amplifying equipment is necessary to ensure accurate communication and make the signal stronger if it needs to go long distances. Broader Definition When many people talk about a network, they are talking about a network using a very broad concept. For instance if someone cannot get to their email, they may say "the network is down". Likewise they may say this if they cannot surf the internet or get to their files. They may not stop to think that in each specific instance there is a single piece of equipment that may provide the capability which they are trying to use. Most people who work on a corporate or organizational network think about the network in component parts. The three main parts are: The cabling and amplifiers mentioned in the first paragraph. The workstations which most members of the organization use to access resources. Higher powered computers called servers - These are the machines that provide what network administrators call services. Services include the functions that most people try to use such as email, reading and writing files, printing, and getting to the internet. Whenever a user is trying to do something on the network, there is a service or machine providing the capability to do so. This even includes times when someone is trying to get to network resources from their home.

Services

Services include:

• Email service
• File service - Allows users to use and share file space on a computer with a lot of file space.
• Print service - Allows printing to printers connected on the network.
• Web surfing - Allowing someone to open web pages and see web sites on the internet.
• Filtering out undesired sites on the internet.
• Allowing someone to access the network from the outside (from home).
• Updating virus definitions on workstations.
• Allowing someone to log onto the network.
• Even giving a workstation an address on the network is a service. If your computer does not have an address, it cannot access the internet or any other resource on the network.

A Typical Network

A typical corporate or organizational network is shown below:

Of course there are variations on this network layout and some details have been left out for the sake of simplicity but this drawing should give you some idea about what goes on behind the scene on the network at your organization. Some servers and server functions have not been shown here.

The firewall is the device that protects all computers in the network from many attacks. It allows some types of network traffic into the network from the outside, but usually only for mail or web services. Usually the internet traffic that that is allowed to come into the network is routed to the part of the network labeled "DMZ" on the right side of the diagram. DMZ stands for demilitarized zone and is also called a semi-private network. In this DMZ is a web server which is used to allow people surfing on the internet to see web pages posted by the organization. A mail server is also shown in the DMZ but this could be replaced by a mail relay server while the mail server is placed inside the private network. The mail relay server would forward mail traffic from the outside to the mail server. This would increase the security of the network since a direct connection from the internet to the mail server would not be allowed.

The private network is of course the most secure part of the network. There are several servers on this network including:

• A login server (called a domain controller) which controls everyones permissions and access to the network resources such as files. Without this server, they cannot login to the network.
• An address server (called a DHCP server) which provides addresses to computers on the network so they can communicate as discussed earlier.
• A file server which provides common files and a private folder for users.
• A remote access server which allows users to connect to the network by telephone from the outside.

Also the workstations are part of this network.

Conclusion

Knowing the above information, if someone cannot get their mail, they may think the network is down. This is not likely to be the case. The mail server may be down but the network is not likely to be down. The same goes for when someone can't surf the web. There may be a problem with the firewall or the line connecting to the internet, but it is unlikely that the whold netwlrk is down. When problems are noticed it is best for the user to describe what they were trying to do and what happened.

from: http://www.comptechdoc.org

Introduction to Algorithms

General Algorithm History

Algorithms were used to solve every day problems long before computers were

ever invented. In fact algorithms have been used for so long they were named for the ninth

century mathematician, Al-Khowarizmi. Algorithms have been used for centuries to solve the

most complex problems that humanity has encountered. One of the most famous algorithms

was imagined in ancient greece. Euclid's algorithm for calculating the greatest common divisor

of two integers had and still does have impacts in the mathematical world. The importance of

algorithms in today's society should not be underestimated. The computer, for example, would

have no purpose since almost all programs are written using an algorithmic approach.

Algorithm Defintions and General Concepts

Webopedia defines an algorithm as:

"A formula or set of steps for solving a particular problem. To be an algorithm, a set of
rules must be unambiguous and have a clear stopping point. Algorithms can be expressed
in any language, from natural languages like English or French to programming languages
like FORTRAN.

We use algorithms every day. For example, a recipe for baking a cake is an algorithm.
Most programs, with the exception of some artificial intelligence applications, consist of
algorithms. Inventing elegant algorithms -- algorithms that are simple and require the fewest
steps possible -- is one of the principal challenges in programming."

Pseudo Code

Pseudo Code is used to represent algorithms in a programming language free context. It is basically a language that is not implemented on a computer. These are the constructs of pseudo code.

variable <-- value

- This means that variable is assigned value.

if (condition) then
statements1
else
statements2

- This is used for making choices in pseudo code. if some condition is true then statements1 is done. if condition is false then statements2 are done.

while {condition} do
statement

-This is used for repeating statements in pseudo code. As condition evaluates to true the statements are done.

repeat until {condition}
statement

- Statements are evaluated until the condition evaluates to statement true, then exit the loop.

for {condition} do
statement

- Evaluates statement as long as condition is true.

Plain English can be used in pseudo code as long as the point is made clear. Math operators can also be used, for example <, >, <, >, and not equals.

Here is an example for an algorithm that will assign the variable x the numbers from 1 to 10 except for 5.

x <-- 0

while x <>
if x = 4 then
x <-- x + 2
else
x <-- x + 1

This is done very simply. x is initialized to 0. The algorithm enters the while loop because 0 <>

Central Processing Unit - CPU

The CPU of a computer is a lot like its brain. Rather than actually thinking, though, it moves data bits around in ways defined by the programmer. It takes data from the program that is running in memory, other sections of memory, and/or input devices, modifies it according to the rules layed out by the programmer, then delivers it to output, disk storage, and/or memory.
Pictured here is a typical CPU chip (known as a socket-7 chip). The actual size of the chip itself is about 2 centimetres square. the rest of the module consist of a plastic case and, pins which connect it to the computer. Some newer models of chips include an external cache in the case as well. It's hard to see at this detail level, but the CPU is made up primarily of transistors. These transistors are grouped into gates which do very simple operations on data bits. These gates are grouped into larger logical units which do useful functions.
The main parts of the CPU are: Control - Decides which operation is being performed. It sends signals to the various multiplexors to decide which output occurs. This peice examines the actual machine instruction code. Registers - Small local storage areas, used to store data about to be manipulated. These vary in size and number depending on the processor. Once 16 bit, now commonly 32 bit, and in the future 64 bit will become more common. They can store numerical values or other data including memory addresses and machine-language instructions. Arithmetic Logic Unit (ALU) - Performs all mathematical operations, such as addition, subtraction, multiplication, division, logical bit shifting. Multiplexors - Select input or output from a number of possible values. These are used to decide input and output in the CPU. Cache - Not always present, but can enhance CPU performance by storing regularly-used values for fast retrieval.
One of the most important sections of the CPU is the Arithmetic Logic Unit, or ALU. This component can do many operations including addition, subtraction, multiplication, and other bit-altering routines like logical AND and OR. Like all main sections of the CPU there are many control lines running to and from the ALU, as well as input and output.
The CPU decides what should be done next by reading instructions from the computer's memory. These instructions are created by a programmer, usually using a high-level language like C, C++, or JAVA. When a high-level program is compiled, it is translated into machine-language instructions. These are in binary format but can be represented by what is called "Assembly language". Essentially this is just the binary instructions translated into human-understandable words.
Comparing CPUs is at the same time difficult and simple. There are a number of ways to evaluate CPU performance. Unfortunately few are very straightforward or accurate. The simplest comparison with which everyone is familar is Clock Speed, usually expressed in Mega-Hertz (MHz). This represents directly the number of calculations per second that the processor can perform.
Not too long ago (March, 2000) the 1 GHz (1 Giga-Hertz = 1000 Mega-Hertz) barrier was broken by two leading chip manufacturing companies, Intel and AMD. In at least one benchmarking test, the Intel Pentium III chip out-did the AMD Athlon by a very small margin. The difference was simply due to materials used to manufacture the chip.
These new CPUs will not work in any computer, so don't go and buy a brand new PIII 1G chip to replace your old 486 chip. Only certain motherboards can accept certain types of chips. The size and shape of the chip itself can vary from model to model. The first chip shown above will fit into a regular pentium slot, know as Socket 7. The next one shown, at the top of this section, is a brand-new Intel Pentium III 1GHz processor. As you can see by the shape and size, this new chip attaches to the motherboard in a completely different way than the Socket 7. Even if the sockets were the same for both chips, the older motherboard could probably not provide enough electricity, or fast enough clock signals to the new chip to make it work.

from: http://www.cs.usask.ca

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from: ilmukomputer.com

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FROM: ILMUKOMPUTER.COM

Visual display unit

A visual display unit, often called simply a monitor, is a piece of electrical equipment which displays viewable images generated by a computer without producing a permanent record. The word "monitor" is used in other contexts; in particular in television broadcasting, where a television picture is displayed to a high standard. A computer display device is usually either a cathode ray tube or some form of flat panel such as a TFT LCD. The monitor comprises the display device, circuitry to generate a picture from electronic signals sent by the computer, and an enclosure or case. Within the computer, either as an integral part or a plugged-in interface, there is circuitry to convert internal data to a format compatible with a monitor.

Diagonal size

The inch size is the diagonal size of the picture tube or LCD panel. With 4:3 CRTs the picture is squarer than 16:10 TFT and so has a larger area for the same diagonal, hence a 17" CRT generally gives about the same area of picture as a 19" TFT.

This method of size measurement dates from the early days of CRT television when round picture tubes were in common use, which only had one dimension that described display size. When rectangular tubes were used, the diagonal measurement of these was equivalent to the round tube's diameter, hence this was used.

A better way to compare CRT and LCD displays is by viewable image size.

As with television, several different hardware technologies exist for displaying computer-generated output:

• Liquid crystal display (LCD). TFT LCDs are the most popular display device for new computers in the world.
  • Passive LCD gives poor contrast and slow response, and other image defects. These were used in some laptops until the mid 1990s.
  • TFT Thin Film Transistor LCDs give much better picture quality in several respects. All modern LCD monitors are TFT.
• Cathode ray tube (CRT)
  • Standard raster scan computer monitors
  • Vector displays, as used on the Vectrex, many scientific and radar applications, and several early arcade machines (notably Asteroids) - always implemented using CRT displays due to requirement for a deflection system, though can be emulated on any raster-based display.
  • Television receivers were used by most early personal and home computers, connecting composite video to the television set using a modulator. Image quality was reduced by the additional steps of composite video ? modulator ? TV tuner ? composite video.
• Plasma display
• Surface-conduction electron-emitter display (SED)
• Video projector - implemented using LCD, CRT, or other technologies. Recent consumer-level video projectors are almost exclusively LCD based.
• Organic light-emitting diode (OLED) display
• Penetron military aircraft displays

From Wikipedia, the free encyclopedia

Keyboard

In computing, a keyboard is a peripheral partially modeled after the typewriter keyboard.

Physically, a keyboard is an arrangement of buttons, or keys. A keyboard typically has characters engraved or printed on the keys; in most cases, each press of a key corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence; other keys do not produce any symbol, but instead affect the operation of the computer or the keyboard itself. See input method editor.

A majority of all keyboard keys produce letters, numbers or signs (characters) that are appropriate for the operator's language. Other keys can produce actions when pressed, and other actions are available by the simultaneous pressing of more than one action key.

There exists a large number of different arrangements of symbols on keys. These different keyboard layouts arise mainly because different people need easy access to different symbols; typically, this is because they are writing in different languages, but specialized keyboard layouts for mathematics, accounting, and computer programming also exist.

Most of the more common keyboard layouts (QWERTY-based and similar) were designed in the era of the mechanical typewriters, so their ergonomics had to be slightly compromised in order to tackle some of the technical limitations of the typewriters. The letters were attached to levers that needed to move freely; because jamming would result if commonly used letters were placed too close to one another, Christopher Sholes invented the QWERTY layout. However, with the advent of modern electronics, this is no longer an issue. QWERTY layouts and their brethren had been a de facto standard for decades prior to the introduction of the very first computer keyboard, and were primarily adopted for electronic keyboards for this reason. Alternative layouts do exist, the best known of which are the Dvorak and more recently Colemak layouts; however, these are not in widespread use.

The number of keys on a keyboard varies from the standard of 101 keys introduced in the late 1980s to the 104-key Windows keyboards and all the way up to 130 keys or more, with many of the additional keys being symbol-less programmable keys that can simulate multiple functions such as starting a web browser or e-mail client. There also were "Internet keyboards," sold in the late 1990s, that replaced the function keys with pre-programmed internet shortcuts. Pressing the shortcut keys would launch a browser to go to that website.

Connection types

This photograph shows a QWERTY keyboard dismantled, with all of the keys properly removed, during the cleaning process.

There are several different ways of connecting a keyboard which have evolved over the years. These include the standard AT (DIN-5) connector commonly found on pre-80486 motherboards, which was eventually replaced by the PS/2 and USB connection. Prior to the iMac line of systems, Apple Computer used ADB, a proprietary system, for its keyboard connector.

Sound card

A sound card (also known as an audio card) is a computer expansion card that facilitates the input and output of audio signals to/from a computer under control of computer programs. 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). Many computers have sound capabilities built in, while others require additional expansion cards to provide for audio capability.

Sound cards usually feature a digital-to-analog converter, that converts recorded or generated digital data into an analog format. The output signal is connected to an amplifier, headphones, or external device using standard interconnects, such as a TRS connector or an RCA connector. If the number and size of connectors is too large for the space on the backplate the connectors will be off-board, typically using a breakout box, or an auxiliary backplate. More advanced cards usually include more than one sound chip to provide for higher data rates and multiple simultaneous functionality, eg between digital sound production and synthesized sounds (usually for real-time generation of music and sound effects using minimal data and CPU time). Digital sound reproduction is usually done with multi-channel DACs, which are capable of multiple digital samples simultaneously at different pitches and volumes, or optionally applying real-time effects like filtering or distortion. Multi-channel digital sound playback can also be used for music synthesis when used with a digitized instrument bank, typically a small amount of ROM or Flash memory containing samples corresponding to MIDI instruments. A contrasting way to synthesize sound on a PC uses "audio codecs", which rely heavily on software for music synthesis, MIDI compliance, and even multiple-channel emulation. This approach has become common as manufacturers seek to simplify the design and the cost of sound cards.

Most sound cards have a line in connector for signal from a cassette tape recorder or similar sound source. The sound card digitizes this signal and stores it (under control of appropriate matching computer software) on the computer's hard disk for storage, editing, or further processing. Another common external connector is the microphone connector, for use by a microphone or other low level input device. Input through a microphone jack is often used by speech recognition software or for Voice over IP applications.

Sound channels and polyphony

8-channel digital-to-analog converter Cirrus Logic CS4382 placed on Sound Blaster X-Fi Fatal1ty

Another important characteristic of sound cards is polyphony, which is more than one distinct voice or sound playable simultaneously and independently, and the number of simultaneous channels. These are intended as the number of distinct electrical audio outputs, which may correspond to a speaker configuration such as 2.0 (stereo), 2.1 (stereo and sub woofer), 5.1 etc.). Sometimes, the terms "voices" and "channels" are used interchangeably to indicate the degree of polyphony, not the output speaker configuration.

For example, many older sound chips could accommodate three voices, but only one audio channel (ie, a single mono output) for output, requiring all voices to be mixed together. More recent cards, such as the AdLib sound card, have a 9 voice polyphony and 1 mono channel as a combined output.

For some years, most PC sound cards have had multiple FM synthesis voices (typically 9 or 16) which were usually used for MIDI music. The full capabilities of advanced cards aren't often completely used; only one (mono) or two (stereo) voice(s) and channel(s) are usually dedicated to playback of digital sound samples, and playing back more than one digital sound sample usually requires a software downmix at a fixed sampling rate. Modern low-cost integrated soundcards (ie, those built into motherboards) such as audio codecs like those meeting the AC'97 standard and even some budget expansion soundcards still work that way. They may provide more than two sound output channels (typically 5.1 or 7.1 surround sound), but they usually have no actual hardware polyphony for either sound effects or MIDI reproduction, these tasks are performed entirely in software. This is similar to the way inexpensive softmodems perform modem tasks in software rather than in hardware).

Also, in the early days of wavetable synthesis, some sound card manufacturers advertised polyphony solely on the MIDI capabilities alone. In this case, the card's output channel is irrelevant (and typically, the card is only capable of two channels of digital sound). Instead, the polyphony measurement solely applies to the amount of MIDI notes the sound card is capable of producing at one given time.

Today, a sound card providing actual hardware polyphony, regardless of the number of output channels, is typically referred to as a "hardware audio accelerator", although actual voice polyphony is not the sole (or even a necessary) prerequisite, with other aspects such as hardware acceleration of 3D sound, positional audio and real-time DSP effects being more important.

Since digital sound playback has become available and provided better performance than synthesis, modern soundcards with hardware polyphony don't actually use DACs with as many channels as voices, but rather perform voice mixing and effects processing in hardware (eventually performing digital filtering and conversions to and from the frequency domain for applying certain effects) inside a dedicated DSP. The final playback stage is performed by an external (in reference to the DSP chip(s)) DAC with significantly fewer channels than voices (e.g., 8 channels for 7.1 audio, which can be divided among 32, 64 or even 128 voices).

Video card

A video card, also referred to as a graphics accelerator card, display adapter, graphics card, and numerous other terms, is an item of personal computer hardware whose function is to generate and output images to a display. It operates on similar principles as a sound card or other peripheral devices.The price range for this device starts from $50 to $6500.

The term is usually used to refer to a separate, dedicated expansion card that is plugged into a slot on the computer's motherboard, as opposed to a graphics controller integrated into the motherboard chipset. An integrated graphics controller may be referred to as an "integrated graphics processor" (IGP).

Some video cards offer added functions, such as video capture, TV tuner adapter, MPEG-2 and MPEG-4 decoding or even FireWire, mouse, light pen, joystick connectors, or even the ability to connect multiple monitors.

Video cards are not used exclusively in IBM type PCs; they have been used in devices such as Commodore Amiga (connected by the slots Zorro II and Zorro III), Apple II, Apple Macintosh, Atari Mega ST/TT (attached to the MegaBus or VME interface), Spectravideo SVI-328, MSX and in video game consoles.

Video card history starts in the 1960s, when printers were replaced with screens as visualization element. Video cards were needed to create the first images.

	Year	Text Mode	Graphics Mode	Colors	Memory
MDA	1981	80*25	-	1	4 KB
CGA	1981	80*25	640*200	16	16 KB
HGC	1982	80*25	720*348	1	64 KB
EGA	1984	80*25	640*350	16	256 KB
IBM 8514	1987	80*25	1024*768	256	-
MCGA	1987	80*25	320*200	256	-
VGA	1987	720*400	640*480	256	256 KB
SVGA	1989	80*25	800*600	256	1 MB
XGA	1990	80*25	1024*768	65,536	2 MB

The first IBM PC video card, which was released with the first IBM PC, was developed by IBM in 1981. The MDA (Monochrome Display Adapter) could only work in text mode representing 25x80 lines in the screen. It had a 4KB video memory and just one color.^[1]

Starting with the MDA in 1981, several video cards were released, which are summarized in the attached table.^[2][3][4][5]

VGA was widely accepted, which lead some corporations such as ATI, Cirrus Logic and S3 to work with that video card, improving its resolution and the number of colours it used. And so was born the SVGA (Super VGA) standard, which reached 2 MB of video memory and a resolution of 1024x768 at 256 color mode.

The evolution of video cards took a turn for the better in 1995 with the release of the first 2D/3D cards, developed by Matrox, Creative, S3 and ATI, among others. Those video cards followed the SVGA standard, but incorporated 3D functions. In 1997, 3dfx released the graphics chip Voodoo, which was very powerful and included new 3D effects (Mip Mapping, Z-buffering, Anti-aliasing...). From this point, a series of 3D video cards were released, like Voodoo2 from 3dfx, TNT and TNT2 from NVIDIA. The power reached with these cards exceeded the PCI port capacity. Intel developed the AGP (Accelerated Graphics Port) which solved the bottleneck between the microprocessor and the video card. From 1999 until 2002, NVIDIA controlled the video card market (taking over 3dfx)^[6] with the GeForce family. The improvements carried out in these years were focused in 3D algorithms and graphics processor clock rate. Nevertheless, video memory also needed to improve their data rate, and DDR technology was incorporated. The capacity of video memory goes in this period from 32 MB with GeForce to 128 MB with GeForce 4.

In 2006, the leadership of the video cards market^[7] was contested between NVIDIA and ATI with their biggest graphics models GeForce and Radeon respectively.

The most common connection systems between the video card and the computer display are:

• HD-15: Analog-based standard adopted in the late 1980s designed for CRT displays, also called VGA connector. Some problems of this standard are electrical noise, image distortion and sampling error evaluating pixels.

• DVI: Digital-based standard designed for displays such as flat-panel displays (LCDs, plasma screens, wide High-definition television displays) and video projectors. It avoids image distortion and electrical noise, corresponding each pixel from the computer to a display pixel, using its native resolution.

• Video In Video Out (VIVO) for S-Video, Composite video and Component video: Included to allow the connection with televisions, DVD players, video recorders and video game consoles. They often come in two 9-pin Mini-DIN connector variations, and the VIVO splitter cable generally comes with either 4 connectors (S-Video in & out+Composite video In & out) or 6 connectors (S-Video In & Out+Component Pb out+Component Pr out+Component Y out (also Composite out)+Composite in).

[edit] Other Types of Connection Systems:

• Composite video: Analog system, with lower resolution. It uses RCA connector.

• Component video: It has three cables, each with RCA connector (YCbCr); it is used in projectors, DVD players and some televisions.

• DB13W3: an analogue standard once used by Sun Microsystems, SGI and IBM.

• HDMI: digital technology released in 2003, whose goal is to replace all the others.

• Display Port: An advanced license and royalty-free digital audio/video interconnect released in 2007.

Computer power supply

A computer power supply unit (Computer PSU) is the component that supplies power to a computer. More specifically, a power supply is typically designed to convert 100-120 V (North America and Japan) or 220-240 V (Europe, Africa, Asia and Australia) AC power from the mains to usable low-voltage DC power for the internal components of the computer. Some power supplies have a switch to change between 230 V and 115 V. Other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits.

The most common computer power supplies are built to conform with the ATX form factor. The most recent specification of the ATX standard is version 2.2, released in 2004. This enables different power supplies to be interchangeable with different components inside the computer. ATX power supplies also are designed to turn on and off using a signal from the motherboard (PS-ON wire, which can be shorted to ground to turn on the PSU outside the computer), and provide support for modern functions such as the standby mode available in many computers.

Power rating

Computer power supplies are rated based on their maximum output power. Typical power ranges are from 300 W to 500 W (lower than 300 W for Small form factor systems). Power supplies used by gamers and enthusiasts sometimes range from 500 W to 1000 W, with the highest end units going up to 2 kW for servers and extreme performance computers with multiple processors, several hard disks and multiple graphics cards (ATI CrossFire or NVIDIA SLI).

Using a power supply that is larger than necessary can significantly increase operating costs by wasting energy. Many overestimate the size of power supply that is needed; several of the online calculators overestimate as well. Typical desktop computers, even those with power hungry processors like the Prescott P4 or a hot GPU, use a maximum of 200 to 250 W or less at full load.

External

Most computer power supplies have the appearance of a square metal box, and have a large bundle of wires emerging from one end. Opposite the wire bundle is the back face of the power supply, with an air vent and C14 IEC connector to supply AC power. There may optionally be a power switch and/or a voltage selector switch. A label on one side of the box lists technical information about the power supply, including safety certifications maximum output wattage. Common certification marks for safety are the UL mark, GS mark, TÜV, NEMKO, SEMKO, DEMKO, FIMKO, CCC, CSA, VDE, GOST R and BSMI. Common certificate marks for EMI/RFI are the CE mark, FCC and C-tick. The CE mark is required for power supplies sold in Europe and India.

Dimensions of an ATX power supply are 150 mm width, 86 mm height, and typically 140 mm depth, although the depth can vary from brand to brand.

Connectors

Various connectors from a computer PSU.

Typically, power supplies have the following connectors:

• PC Main power connector (usually called P1): Is the connector that goes to the motherboard to provide it with power. The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire mentioned above (it is usually green). This connector is the largest of all the connectors. In older AT power supplies, this connector was split in two: P8 and P9. If you have a power supply with 24-pin connector, you can plug it into a motherboard with a 20-pin connector. In cases where the motherboard has a 24-pin connector, some power supplies come with two connectors (one with 20-pin and other with 4-pin) which can be used together to form the 24-pin connector.
• ATX12V 4-pin power connector (also called the P4 power connector). A second connector that goes to the motherboard (in addition to the main 24-pin connector). This connector is found on recent motherboards.
• 4-pin Peripheral power connectors (usually called Molex for its manufacturer): These are the other, smaller connectors that go to the various disk drives of the computer. Most of them have four wires: two black, one red, and one yellow. Unlike the standard mains electrical wire color-coding, each black wire is a ground, the orange wire is +3.3 V, the red wire is +5 V, and the yellow wire is +12 V.
• 4-pin Floppy drive power connectors (usually called Mini-connector): This is one of the smallest connectors that supplies the floppy drive with power. In some cases, it can be used as an auxiliary connector for AGP video cards. Its cable configuration is similar to the Peripheral connector.
• Auxiliary power connectors: There are several types of auxiliary connectors designed to provide additional power if it is needed.
• Serial ATA power connectors: a 15-pin connector for components which use SATA power plugs. This connector supplies power at three different voltages: +3.3, +5, and +12 volts.
• Most modern computer power supplies include 6-pin connectors which are generally used for PCI Express graphics cards, but a newly introduced 8-pin connector should be seen on the latest model power supplies. Each PCI Express 6-pin connector can output a maximum of 75 W.
• A C14 IEC connector with an appropriate C13 cord is used to attach the power supply to the local power grid.

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Inside the computer power supply is a complex arrangement of electrical components, including diodes, capacitors, transistors and transformers. Also, most computer power supplies have metal heat sinks and fans to dissipate the heat produced. The speed of the fan is often dependent on the temperature, or less often the power load. It may be dangerous to open a power supply even if it is not connected to an electrical outlet, as high voltages may still be present in charged capacitors. However, for most PSUs this can be fixed by unplugging the PSU and then pressing the power-on button, which will drain the capacitors. Still, care should be taken as some PSUs require a load on the output in order to discharge the capacitors fully. Even when the PC is turned off, a PSU will draw some power from the electrical outlet, most of it going to power the +5 VSB (standby voltage) rail.

Some models even include heat pipes to assist in heat dissipation.

AT vs. ATX

A typical installation of an ATX form factor computer power supply.

There are two basic differences between old AT and newer ATX power supplies:

• The PC main connectors (see above description of connectors).
• The soft switch. On older AT power supplies, the Power-on switch wire from the front of the computer is connected directly to the power supply. On newer ATX power supplies, the switch goes to the motherboard, allowing other hardware or software to turn the system on or off.

Wiring diagrams

AT power connector (Used on older AT style mainboards)

Color	Pin	Signal
	P8.1	Power Good
	P8.2	+5 V
	P8.3	+12 V
	P8.4	−12 V
	P8.5	Ground
	P8.6	Ground
	P9.1	Ground
	P9.2	Ground
	P9.3	−5 V
	P9.4	+5 V
	P9.5	+5 V
	P9.6	+5 V

24-pin ATX power supply connector
(20-pin omits the last 4: 11, 12, 23 and 24)

Color	Signal	Pin	Pin	Signal	Color
	+3.3 V	1	13	+3.3 V sense
	+3.3 V	2	14	−12 V
	Ground	3	15	Ground
	+5 V	4	16	Power on
	Ground	5	17	Ground
	+5 V	6	18	Ground
	Ground	7	19	Ground
	Power good	8	20	−5 V (optional)
	+5 V standby	9	21	+5 V
	+12 V	10	22	+5 V
	+12 V	11	23	+5 V
	+3.3 V	12	24	Ground

Motherboard/Logicboard

• Motherboard - the "body" of the computer, through which all other components interface.
• Central processing unit (CPU) - Performs most of the calculations which enable a computer to function, sometimes referred to as the "brain" of the computer.
  • Computer fan - Used to lower the temperature of the computer; a fan is almost always attached to the CPU, and the computer case will generally have several fans to maintain a constant airflow. Liquid cooling can also be used to cool a computer, though it focuses more on individual parts rather than the overall temperature inside the chassis.
• Random Access Memory (RAM) - Fast-access memory that is cleared when the computer is powered-down. RAM attaches directly to the motherboard, and is used to store programs that are currently running.
• Firmware is loaded from the Read only memory ROM run from the Basic Input-Output System (BIOS) or in newer systems Extensible Firmware Interface (EFI) compliant
• Internal Buses - Connections to various internal components.
  • PCI
  • PCI-E
  • USB
  • HyperTransport
  • CSI (expected in 2008)
  • AGP (being phased out)
  • VLB (outdated)
• External Bus Controllers - used to connect to external peripherals, such as printers and input devices. These ports may also be based upon expansion cards, attached to the internal buses.
  • parallel port (outdated)
  • serial port (outdated)
  • USB
  • firewire
  • SCSI (On Servers and older machines)
  • PS/2 (For mice and keyboards, being phased out and replaced by USB.)
  • ISA (outdated)
  • EISA (outdated)
  • MCA (outdated)