RAM & ROM

What is RAM?
RAM stands for Random Access Memory. RAM provides space for your computer to read and write data to be accessed by the CPU (central processing unit). When people refer to a computer's memory, they usually mean its RAM.
New computers typically come with at least 256 megabytes (MB) of RAM installed, and can be upgraded to 512MB or even a gigabyte or more.
If you add more RAM to your computer, you reduce the number of times your CPU must read data from your hard disk. This usually allows your computer to work considerably faster, as RAM is many times faster than a hard disk.
RAM is volatile, so data stored in RAM stays there only as long as your computer is running. As soon as you turn the computer off, the data stored in RAM disappears.
When you turn your computer on again, your computer's boot firmware (called BIOS on a PC) uses instructions stored semi-permanently in ROM chips to read your operating system and related files from the disk and load them back into RAM.
Note: On a PC, different parts of RAM may be more or less easily accessible to programs. For example, cache RAM is made up of very high-speed RAM chips which sit between the CPU and main RAM, storing (i.e., caching) memory accesses by the CPU. Cache RAM helps to alleviate the gap between the speed of a CPU's megahertz rating and the ability of RAM to respond and deliver data. It reduces how often the CPU must wait for data from main memory.
RAM Defined
RAM (random access memory) is the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor. RAM is much faster to read from and write to than the other kinds of storage in a computer, the hard disk, floppy disk, and CD-ROM. However, the data in RAM stays there only as long as your computer is running. When you turn the computer off, RAM loses its data. When you turn your computer on again, your operating system and other files are once again loaded into RAM, usually from your hard disk.
RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term memory focuses on work at hand, but can only keep so many facts in view at one time. If short-term memory fills up, your brain sometimes is able to refresh it from facts stored in long-term memory. A computer also works this way. If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in RAM with new, slowing down the computer's operation. Unlike the hard disk which can become completely full of data so that it won't accept any more, RAM never runs out of memory. It keeps operating, but much more slowly than you may want it to.
How Big is RAM?
RAM is small, both in physical size (it's stored in microchip modules) and in the amount of data it can hold. It's much smaller than your hard disk. A typical computer may come with 32 million bytes of RAM and a hard disk that can hold 4 billion bytes. RAM comes in the form of "discrete" (meaning separate) microchip modules that plug into holes in the computer's motherboard. These holes connect through a bus or set of electrical paths to the processor. The hard drive, on the other hand, stores data on a magnetized surface that looks like a phonograph record.
Today's personal computers come with 16 or more megabytes of RAM, usually increasing in multiples of 8 megabytes. Users of graphic applications usually need 32, 64, or 128 or even more megabytes of memory. Most personal computers are designed to allow you to add additional RAM modules up to a certain limit (for example, up to 64 or 128 megabytes). Having more RAM in your computer reduces the number of times that the computer processor has to read data in from your hard disk, an operation that takes much longer than reading data from RAM. (RAM access time is expressed in nanoseconds; hard disk access time is expressed in milliseconds.)
Why Random Access
RAM is called "random access" because any storage location can be accessed directly. Originally, the term distinguished regular core memory from offline memory, usually on magnetic tape in which an item of data could only be accessed by starting from the beginning of the tape and finding an address sequentially. Perhaps it should have been called "nonsequential memory" because RAM access is hardly random. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations. A term IBM has preferred is direct access storage or memory. Note that other forms of storage such as the hard disk and CD-ROM are also accessed directly (or "randomly") but the term random access is not applied to these forms of storage.
In addition to disk, floppy disk, and CD-ROM storage, another important form of storage is read-only memory (ROM), a more expensive kind of memory that retains data even when the computer is turned off. Every computer comes with a small amount of ROM that holds just enough programming so that the operating system can be loaded into RAM each time the computer is turned on.
Briefly How RAM Works
What RAM Looks Like
In general, RAM is much like an arrangement of post-office boxes in which each box can hold a 0 or a 1. Each box has a unique address that can be found by counting across columns and then counting down by row. In RAM, this set of post-office boxes is known as an array and each box is a cell. To find the contents of a box (cell), the RAM controller sends the column/row address down a very thin electrical line etched into the chip. There is an address line for each row and each column in the set of boxes. If data is being read, the bits that are read flow back on a separate data line. In describing a RAM chip or module, a notation such as 256Kx16 means 256 thousand columns of cells standing 16 rows deep.
In the most common form of RAM, dynamic RAM, each cell has a charge or lack of charge held in something similar to an electrical capacitor. A transistor acts as a gate in determining whether the value in the capacitor can be read or written. In static RAM, instead of a capacitor-held charge, the transistor itself is a positional flip/flop switch, with one position meaning 1 and the other position meaning 0.
Externally, RAM is a chip that comes embedded in a personal computer motherboard with a variable amount of additional modules plugged into motherboard sockets. To add memory to your computer, you simply add more RAM modules in a prescribed configuration. These are single in-line memory modules (SIMMs) or dual in-line memory modules (DIMMs). Since DIMMs have a 64-bit pin connection, they can replace two 36-bit (32-bits plus 4 parity bits) SIMMs when synchronous DRAM is used. Laptop and notebook computers contain smaller 32-bit DIMMs known as small outline DIMMs (SO DIMMs).
How Data Is Accessed
When the processor or CPU gets the next instruction it is to perform, the instruction may contain the address of some memory or RAM location from which data is to be read (brought to the processor for further processing). This address is sent to the RAM controller. The RAM controller organizes the request and sends it down the appropriate address lines so that transistors along the lines open up the cells so that each capacitor value can be read. A capacitor with a charge over a certain voltage level represents the binary value of 1 and a capacitor with less than that charge represents a 0. For dynamic RAM, before a capacitor is read, it must be power-refreshed to ensure that the value read is valid. Depending on the type of RAM, the entire line of data may be read that the specific address happens to be located at or, in some RAM types, a unit of data called a page is read. The data that is read is transmitted along the data lines to the processor's nearby data buffer known as level-1 cache and another copy may be held in level-2 cache.
For video RAM, the process is similar to DRAM except that, in some forms of video RAM, while data is being written to video RAM by the processor, data can simultaneously be read from RAM by the video controller (for example, for refreshing the display image).
How RAM Effectiveness is Measured
The amount of time that RAM takes to write data or to read it once the request has been received from the processor is called the access time. Typical access times vary from 9 nanoseconds to 70 nanoseconds, depending on the kind of RAM. Although fewer nanoseconds is better, user-perceived performance is based on coordinating access times with the computer's clock cycles. Access time consists of latency and transfer time. Latency is the time to coordinate signal timing and refresh data after reading it.
Kinds of RAM
RAM can be divided into (1) main RAM, which stores every kind of data and makes it quickly accessible to a microprocessor and (2) video RAM, which stores data intended for your display screen, enabling images to get to your display faster.
Main RAM
Main RAM can be divided into static RAM (SRAM) and dynamic RAM (DRAM).
Static RAM (SRAM)
Static RAM is more expensive, requires four times the amount of space for a given amount of data than dynamic RAM, but, unlike dynamic RAM, does not need to be power-refreshed and is therefore faster to access. One source gives a typical access time as 25 nanoseconds in contrast to a typical access time of 60 nanoseconds for dynamic RAM. (More recent advances in dynamic RAM have improved access time.) Static RAM is used mainly for the level-1 and level-2 caches that the microprocessor looks in first before looking in dynamic RAM.
Burst (or SynchBurst) Static RAM (BSRAM)
Burst SRAM (also known as SynchBurst SRAM) is synchronized with the system clock or, in some cases, the cache bus clock. This allows it be more easily synchronized with any device that accesses it and reduces access waiting time. It is used as the external level-2 cache memory for the Pentium II microprocessor chipset.
Dynamic RAM (DRAM)
Dynamic RAM uses a kind of capacitor that needs frequent power refreshing to retain its charge. Because reading a DRAM discharges its contents, a power refresh is required after each read. Apart from reading, just to maintain the charge that holds its content in place, DRAM must be refreshed about every 15 microseconds. DRAM is the least expensive kind of RAM.
Fast Page Mode DRAM (FPM DRAM)
Prior to newer forms of DRAM, Fast Page Mode DRAM (FPM DRAM) was the most common kind of DRAM in personal computers. Page mode DRAM essentially accesses a row of RAM without having to continually respecify the row. A row access strobe (RAS) signal is held active while the column access strobe (CAS) signal changes to read a sequence of contiguous cells. This reduces access time and lowers power requirements. Clock timings for FPM DRAM are typically 6-3-3-3 (meaning 3 clock cycles for access setup, and 3 clock cycles for the first and each of three successive accesses based on the initial setup).
Enhanced DRAM
Enhanced DRAM (EDRAM) is the combination of SRAM and DRAM in a single package that is usually used for a level-2 cache. Typically, 256 bytes of static RAM is included along with the dynamic RAM. Data is read first from the faster (typically 15 nanoseconds) SRAM and if it is not found there, it is read from the DRAM, typically at 35 nanoseconds.
Extended Data Output RAM or DRAM (EDO RAM or EDO DRAM)
Extended Data Output RAM (EDO RAM) or Extended Data Output Dynamic RAM (EDO DRAM) is up to 25% faster than standard DRAM and reduces the need for level-2 cache memory.
Burst Extended Data Output DRAM (BEDO DRAM)
BEDO DRAM improves page mode DRAM by "building in" three successive column address shifts after the first column address is specified so that four bits are read as a burst. Together with a dual-bank architecture, BEDO DRAM promised to offer 4-1-1-1 access times. However, because Intel and other manufacturers preferred SDRAM, BEDO DRAM was not widely used.
Nonvolatile RAM (NVRAM)
Nonvolatile RAM (NVRAM) is a special kind of RAM that retains data when the computer is turned off or there is a power failure. Like the computer's read-only memory (ROM), it is powered by a battery within the computer. It can also work by writing its contents to and restoring them from an EEPROM.
Synchronous DRAM (SDRAM)
Synchronous DRAM (SDRAM) is a generic name for various kinds of DRAM that are synchronized with the clock speed that the microprocessor is optimized for. This tends to increase the number of instructions that the processor can perform in a given time. The speed of SDRAM is rated in MHz rather than in nanoseconds (ns). This makes it easier to compare the bus speed and the RAM chip speed. You can convert the RAM clock speed to nanoseconds by dividing the chip speed into 1 billion ns (which is one second). For example, an 83 MHz RAM would be equivalent to 12 ns.
JEDEC SDRAM
JEDEC (Joint Electron Device Engineering Council) SDRAM is an industry standard synchronous DRAM. It has a dual-bank architecture and several burst mode accesses that can be preset. JEDEC SDRAM chips operate at either 83 MHz or 100 MHz. JEDEC SDRAM is also known as PC66 SDRAM because it was originally rated for 66 MHz bus operation and to distinguish it from Intel's PC100 architecture.
PC100 SDRAM
PC100 SDRAM is SDRAM that states that it meets the PC100 specification from Intel. Intel created the specification to enable RAM manufacturers to make chips that would work with Intel's i440BX processor chipset. The i440BX was designed to achieve a 100 MHz system bus speed. Ideally, PC100 SDRAM would work at the 100 MHz speed, using a 4-1-1-1 access cycle. It's reported that PC100 SDRAM will improve performance by 10-15% in an Intel Socket 7 system (but not in a Pentium II because its L2 cache speed runs at only half of processor speed).
Double Data Rate SDRAM (DDR SDRAM)
Double Data Rate SDRAM can theoretically improve RAM speed to at least 200 MHz. It activates output on both the rising and falling edge of the system clock rather than on just the rising edge, potentially doubling output. It's expected that a number of Socket 7 chipset makers will support this form of SDRAM.
Enhanced SDRAM (ESDRAM)
Enhanced SDRAM (ESDRAM), made by Enhanced Memory Systems, includes a small static RAM (SRAM) in the SDRAM chip. This means that many accesses will be from the faster SRAM. In case the SRAM doesn't have the data, there is a wide bus between the SRAM and the SDRAM because they are on the same chip. ESDRAM is apparently competing with DDR SDRAM as a faster SDRAM chip for Socket 7 processors.
Direct Rambus DRAM (DRDRAM)
Direct Rambus DRAM (DRDRAM) is a proprietary technology proposed by Rambus, Inc. in partnership with Intel. Like SLDRAM, it promises RAM speed up to 800 MHz. It has a smaller bus width (16 bits compared to 64 bits) than current SDRAM designs.
SyncLink DRAM (SLDRAM)
SyncLink DRAM is, along with Direct Rambus DRAM (DRDRAM), a protocol-based approach. In this approach, all signals to RAM are on the same line (rather than having separate CAS, RAS, address, and data lines). Since access time does not depend on synchronizing operations on multiple lines, SLDRAM promises RAM speed of up to 800 MHz. Like Double Data Rate SDRAM, SLDRAM can operate at twice the system clock rate. SyncLink is an open industry standard that is expected to compete and perhaps prevail over Direct Rambus DRAM.
Ferroelectric RAM (FRAM)
FRAM (ferroelectric RAM) is random access memory that combines the fast read and write access of dynamicRAM (DRAM) - the most common kind of personal computer memory - with the ability to retain data whenpower is turned off (as do other non-volatile memory devices such as ROM and flash memory). Because FRAMis not as dense (can not store as much data in the same space) as DRAM and SRAM, it is not likely replacethese technologies. However, because it is fast memory with a very low power requirement, it is expected tohave many applications in small consumer devices such as personal digital assistants (PDAs), handheld phones,power meters, and smart cards, and in security systems. FRAM is faster than flash memory. It is also expectedto replace EEPROM and SRAM for some applications and to become a key component in future wireless products.
In spite of its name, ferroelectric RAM does not contain iron. Today's FRAM uses lead zirconate titanate (PZT); other materials arebeing considered. The main developer of FRAM is Ramtron International.
Video RAM
Video RAM as "video RAM" means in general all forms of RAM used to store image data for the video display monitor. Somewhat confusingly, the most common type of video RAM is called Video RAM (VRAM). All types of video RAM are special arrangements of dynamic RAM (DRAM). Video RAM is really a buffer between the processor and the display monitor and is often called the frame buffer. When images are to be sent to the display, they are first read by the processor as data from some form of main storage RAM and then written to video RAM. From video RAM (the frame buffer), the data is converted by a RAM digital-to-analog converter (RAMDAC) into analog signals that are sent to the display presentation mechanism such as a cathode ray tube (CRT). Usually, video RAM comes in a 1 or 2 megabyte package and is located on the video or graphics card in the computer. Most forms of video RAM are dual-ported. While the processor is writing a new image to video RAM, the display is reading from video to refresh its current display content. The dual-port design is the main difference between main storage RAM and video RAM.
RAMDAC
RAMDAC (random access memory digital-to-analog converter) is a microchip that converts digital image data into the analog data needed by a computer display. A RAMDAC microchip is built into the video adapter in a computer. It combines a small static RAM (SRAM) containing a color table with three digital-to-analog converters (DACs) that change digital image data into analog signals that are sent to the display's color generators, one for each primary color - red, green, and blue. In a cathode ray tube (CRT) display, an analog signal is sent to each of three electron guns. With displays using other technologies, the signals are sent to a corresponding mechanism.
The SRAM part of the RAMDAC contains a color palette table. A logical color number in the digital data input to SRAM is used to generate three separate values obtained from the table - one for each of red, green, and blue - that are output to one of three digital-to-analog converters. The analog signal output from the converter is input directly to the display electron guns or other image projecting mechanisms. For displays with true color, the digital color data is fed directly to the DACs, bypassing the SRAM table, which is not needed.
Video RAM
Video RAM (VRAM) is the vanilla flavor of video RAM. It is dual-ported, allowing the processor to write to it at the same time that it is refreshing the image on the display monitor.
Synchronous Graphics RAM
Synchronous Graphics RAM (SGRAM) is clock-synchronized RAM that is used for video memory. It is relatively low-cost video memory. It uses masked write, which enables selected data to be modified in a single operation rather as a sequence of read, update, and write operations. It also uses block write, which allows data for background or foreground image fills to be handled more efficiently. SGRAM is single-ported. Its special features are what make it a moderately fast form of video memory. The Matrox Mystique is an example of a video card that uses SGRAM.
Window RAM
Window RAM (WRAM), unrelated to Microsoft Windows, is very high-performance video RAM that is dual-ported and has about 25% more bandwidth than VRAM but costs less. It has features that make it more efficient to read data for use in block fills and text drawing. It can be used for very high resolution (such as 1600 by 1200 pixels) projection using true color). It's used in the Matrox Millenium video card.
Multibank Dynamic RAM
Multibank Dynamic RAM (MDRAM) is a high-performance RAM, developed by MoSys, that divides memory into multiple 32 KB parts or "banks" that can be accessed individually. Traditional video RAM is monolithic; the entire frame buffer is accessed at one time. Having individual memory banks allows accesses to be interleaved concurrently, increasing overall performance. It's also cheaper since, unlike other forms of video RAM, cards can be manufactured with just the right amount of RAM for a given resolution capability instead of requiring it to be in multiples of megabytes.
Rambus Dynamic RAM
Rambus Dynamic RAM (RDRAM) is a video RAM designed by Rambus that includes a proprietary bus that speeds up the data flow between video RAM and the frame buffer. It's optimized for video streaming.
The RAM Table
RAM Technology
Application and Computer Location
Access Speed Range
Ports
Characteristics
Static RAM (SRAM)
level-1 and level-2 cache memoryAlso used in RAMDAC
Fast
One
RAM that is continually chargedMore expensive than DRAM
Burst SRAM (BSRAM)
Level-2 cache memory
Fast
One
SRAM in burst mode
DRAM
Main memoryLow-cost video memory
Slow
One
A generic term for any kind of dynamic (constantly recharged) RAM
FPM (Fast Page Mode) DRAM
Main memoryLow-cost video memory
Slow
One
Prior to EDO DRAM, the most common type of DRAM
EDO (Extended Data Out) DRAM
Main memoryLow-cost video memory
5-20% faster than FPM DRAM
One
Uses overlapping reads (one can begin while another is finishing)Currently, the most common type of DRAM
BEDO (Burst Extended Data Out) DRAM
Main memory and low-cost video
Faster than EDO DRAM4-1-1-1 at 66 MHz
One
Not widely used because not supported by processor chipset makers
EDRAM (Enhanced DRAM)
Level-2 cache memory
15 ns access to SRAM35 ns access to DRAM
One
Contains a 256-byte SRAM inside a larger DRAM
Nonvolatile RAM (NVRAM)
Preset phone numbers and profiles in modems
Fast
One
Battery-powered RAM
Synchronous DRAM (SDRAM)
Main memory
See specific forms of SDRAMRated in MHz rather than nanoseconds
One
Generic term for DRAMs with a synchronous interface
JEDEC Synchronous DRAM (JEDEC SDRAM)
Main memory
Fast
One
Dual-bank architectureBurst modeMost common form of SDRAM
PC100 Synchronous DRAM (PC100 SDRAM)
Main memory
Intended to run at 100 MHz with 4-1-1-1 timing
One
An Intel specification designed to work with their i440BX
Double Data Rate Synchronous DRAM (DDR DRAM)
Main memory
Up to 200 MHz
One
Activates output on both the up and the down part of the clock cycle, doubling the data rate of PC100 SDRAM
Enhanced Synchronous DRAM (ESDRAM)
Main memory
Fast (100 MHz +)
Two
Twice as fast as SDRAMSee Enhanced Memory Systems (EMS)
SyncLink DRAM (SLDRAM)
Main memory
Fastest (200 MHz +)
One
Open protocol-based designUses "packets" for address, data, and control signals
Direct Rambus DRAM (DRDRAM)
Main memory
Up to 800 MHz but with a 16-bit bus width
One
Backed by Intel and Rambus Inc.
Ferroelectric RAM (FRAM)
Main memory in small devices
?
?
Developed by Ramtron
RAMDAC
Video card
Fast
One
Uses a small SRAM to store the color palette table used to provide data for digital-to-analog conversion
Rambus DRAM (RDRAM)
Video memory for Nintendos
Up to 600 MHz
One
Intel and Rambus Inc. architecture
Synchronous Graphics RAM (SGRAM)
Moderate to high-end video memory
Closer to VRAM than DRAM
One
Has special performance-enhancing featuresExample: Matrox Mystique
VRAM (Video RAM)
Higher-cost video memory
Twice the speed of DRAM
Two
Dual-ported, meaning a new image can be stored in RAM while a previous image is being sent to the display
WRAM (Window RAM)
Less expensive video memory
25% faster than VRAM
Two
With RAMDAC, can handle true color at 1600 by 1200 pixel resolution
Multibank DRAM (MDRAM)
Low-cost high-end video memory applications
Faster
One
Interleaved memory accesses between banksMemory has multiple 32 kilobyte banks that can be accessed independentlyCan be manufactured to fit the amount of memory the card requiresNo size-related performance penalty


ROM
Pronounced rahm, acronym for read-only memory, computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read.
Unlike main memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile.
Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs.
A variation of a ROM is a PROM (programmable read-only memory). PROMs are manufactured as blank chips on which data can be written with a special device called a PROM programmer .
Read-Only Memory or ROM is an integrated-circuit memory chip that contains configuration data. ROM is commonly called firmware because its programming is fully embedded into the ROM chip. As such, ROM is a hardware and software in one.
Because data is fully incorporated at the ROM chip's manufacture, data stored can neither be erased nor replaced. This means permanent and secure data storage. However, if a mistake is made in manufacture, a ROM chip becomes unusable. The most expensive stage of ROM manufacture, therefore, is creating the template. If a template is readily available, duplicating the ROM chip is very easy and affordable.
A ROM chip is also non volatile so data stored in it is not lost when power is turned off.
RAM versus ROM
Both RAM and ROM provide the user random access to stored data. However, RAM provides only short-term memory since data stored in RAM is lost when power is turned off. ROM, on the other hand, provides long-term storage since data is permanently etched into the ROM chip.
One other difference between the two is that RAM's data can frequently and speedily be altered and changed at will. ROM cannot be reconfigured at all.
ROM Chip Manufacture
The ROM chip has a matrix of columns and rows. The point of intersection between the column and the row is called a cell. Each cell will have a value of either 1 or 0. The manufacturer of the ROM chip has to determine each cell's value before the ROM manufacture ensues.
After the program has been designed, the ROM chip can now be made. At each cell where the value should be 1, a diode is placed to connect column to row. At each cell where the value should be 0, no diode is placed.
The ROM Chip's Diode
The diode is the cell's electronic check valve. Its main function in the ROM chip is to control and direct the flow of electric current in cells. Specifically, it transfers the electric current from column to row.
The diode has a minimum voltage requirement, what is commonly called the forward breakover, which needs to be surpassed before the diode will transfer the charge from the column to the row of the cell. The usual ROM diode forward breakover voltage is around 0.6 volts.
The ROM activates cells by sending through voltage that is more than the cells' diode forward breakover. The charge that is directed through the column gets passed on by the diode to the appropriate grounded row. Since charge is successfully transmitted from column to row, the cell where a diode is present has a value of 1.
In the ROM circuit, passing a charge through the column will not affect the cells whose values are supposed to be 0. In any cell, this charge cannot be passed from column to row if there's no diode to facilitate the transfer. Therefore, once a cell's value has been determined to be 0, it will permanently be 0.
How Graphics Cards Work
by Tracy V. Wilson and Jeff Tyson

Inside This Article
1.
Introduction to How Graphics Cards Work
2.
Processor and Memory
3.
Input and Output
4.
Choosing a Good Graphics Card
5.
Lots More Information
6.
See all Hardware articles
The images you see on your monitor are 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 the motherboard, 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.
The graphics card creates a wire frame image, then fills it in and adds textures and shading.
Graphics Card BasicsThink of a computer as a company with its own art department. When people in the company want a piece of artwork, they send a request to the art department. The art department decides how to create the image and then puts it on paper. The end result is that someone's idea becomes an actual, viewable picture.
Photo courtesy of HowStuffWorks ShopperThe four main components of a graphics card are connections for the motherboard and monitor, a processor, and memory.
A graphics card works along the same principles. The CPU, working in conjunction with software applications, sends information about the image to the graphics card. The graphics card decides how to use the pixels on the screen to create the image. It then sends that information to the monitor through a cable.
The Evolution of Graphics Cards
Graphics cards have come a long way since IBM introduced the first one in 1981. Called a Monochrome Display Adapter (MDA), the card provided text-only displays of green or white text on a black screen. Now, the minimum standard for new video cards is Video Graphics Array (VGA), which allows 256 colors. With high-performance standards like Quantum Extended Graphics Array (QXGA), video cards can display millions of colors at resolutions of up to 2040 x 1536 pixels.
Creating an image out of binary data is a demanding process. To make a 3-D image, the graphics card first creates a wire frame out of straight lines. Then, it rasterizes the image (fills in the remaining pixels). It also adds lighting, texture and color. For fast-paced games, the computer has to go through this process about sixty times per second. Without a graphics card to perform the necessary calculations, the workload would be too much for the computer to handle.
The graphics card accomplishes this task using four main components:
· A motherboard connection for data and power
· A processor to decide what to do with each pixel on the screen
· Memory to hold information about each pixel and to temporarily store completed pictures
· A monitor connection so you can see the final result
Next, we'll look at the processor and memory in more detail.


NEXT
Inside This Article
1.
Introduction to How Graphics Cards Work
2.
Processor and Memory
3.
Input and Output
4.
Choosing a Good Graphics Card
5.
Lots More Information
6.
See all Hardware articles
Key Combination Result [Alt] and [Esc] Switch between running applications [Alt] and [Tab] Toggle between running applications [Alt] and letter Select menu item by underlined letter [Ctrl] and [Esc] Open Program Menu [Ctrl] and [F4] Close active document or group windows (does not work with some applications) [Alt] and [F4] Quit active application or close current window [Alt] and [-] Open Control menu for active document [Alt] and [Spacebar] Open Control menu for active application [Ctrl] Lft., Rt. arrow Move cursor forward or back one word [Ctrl] Up, Down arrow Move cursor forward or back one paragraph [Ctrl] and X Cut selected text or object(s) [Ctrl] and C Copy selected text or object(s) [Ctrl] and V Paste copied text or object(s) [F1] Open Help for active application Windows+E Open Windows Explorer Windows+F Open Find Windows+M Minimize all open windows Shift+Windows+M Undo minimize all open windows Windows+R Open Run window Windows+F1 Open Windows Help Windows+Tab Cycle through the Taskbar buttons Windows+Break Open the System Properties dialog box

Basic Commands in MS-DOS and Unix

MS-DOS and command line overview
Below is a listing of each of the MS-DOS commands currently listed on Computer Hope and a brief explanation of what each of the commands do. The below commands are all MS-DOS commands, which means not all the below commands will work in your version of MS-DOS and/or Windows command line. Clicking on the command will open the help page for that command with full details about it.
COMMAND
DESCRIPTION
ANSI.SYS
Defines functions that change display graphics, control cursor movement, and reassign keys.
APPEND
Causes MS-DOS to look in other directories when editing a file or running a command.
ARP
Displays, adds, and removes arp information from network devices.
ASSIGN
Assign a drive letter to an alternate letter.
ASSOC
View the file associations.
AT
Schedule a time to execute commands or programs.
ATMADM
Lists connections and addresses seen by Windows ATM call manager.
ATTRIB
Display and change file attributes.
BATCH
Recovery console command that executes a series of commands in a file.
BOOTCFG
Recovery console command that allows a user to view, modify, and rebuild the boot.ini
BREAK
Enable / disable CTRL + C feature.
CACLS
View and modify file ACL's.
CALL
Calls a batch file from another batch file.
CD
Changes directories.
CHCP
Supplement the International keyboard and character set information.
CHDIR
Changes directories.
CHKDSK
Check the hard disk drive running FAT for errors.
CHKNTFS
Check the hard disk drive running NTFS for errors.
CHOICE
Specify a listing of multiple options within a batch file.
CLS
Clears the screen.
CMD
Opens the command interpreter.
COLOR
Easily change the foreground and background color of the MS-DOS window.
COMMAND
Opens the command interpreter.
COMP
Compares files.
COMPACT
Compresses and uncompress files.
CONTROL
Open Control Panel icons from the MS-DOS prompt.
CONVERT
Convert FAT to NTFS.
COPY
Copy one or more files to an alternate location.
CTTY
Change the computers input/output devices.
DATE
View or change the systems date.
DEBUG
Debug utility to create assembly programs to modify hardware settings.
DEFRAG
Re-arrange the hard disk drive to help with loading programs.
DEL
Deletes one or more files.
DELETE
Recovery console command that deletes a file.
DELTREE
Deletes one or more files and/or directories.
DIR
List the contents of one or more directory.
DISABLE
Recovery console command that disables Windows system services or drivers.
DISKCOMP
Compare a disk with another disk.
DISKCOPY
Copy the contents of one disk and place them on another disk.
DOSKEY
Command to view and execute commands that have been run in the past.
DOSSHELL
A GUI to help with early MS-DOS users.
DRIVPARM
Enables overwrite of original device drivers.
ECHO
Displays messages and enables and disables echo.
EDIT
View and edit files.
EDLIN
View and edit files.
EMM386
Load extended Memory Manager.
ENABLE
Recovery console command to enable a disable service or driver.
ENDLOCAL
Stops the localization of the environment changes enabled by the setlocal command.
ERASE
Erase files from computer.
EXIT
Exit from the command interpreter.
EXPAND
Expand a Microsoft Windows file back to it's original format.
EXTRACT
Extract files from the Microsoft Windows cabinets.
FASTHELP
Displays a listing of MS-DOS commands and information about them.
FC
Compare files.
FDISK
Utility used to create partitions on the hard disk drive.
FIND
Search for text within a file.
FINDSTR
Searches for a string of text within a file.
FIXBOOT
Writes a new boot sector.
FIXMBR
Writes a new boot record to a disk drive.
FOR
Boolean used in batch files.
FORMAT
Command to erase and prepare a disk drive.
FTP
Command to connect and operate on a FTP server.
FTYPE
Displays or modifies file types used in file extension associations.
GOTO
Moves a batch file to a specific label or location.
GRAFTABL
Show extended characters in graphics mode.
HELP
Display a listing of commands and brief explanation.
IF
Allows for batch files to perform conditional processing.
IFSHLP.SYS
32-bit file manager.
IPCONFIG
Network command to view network adapter settings and assigned values.
KEYB
Change layout of keyboard.
LABEL
Change the label of a disk drive.
LH
Load a device driver in to high memory.
LISTSVC
Recovery console command that displays the services and drivers.
LOADFIX
Load a program above the first 64k.
LOADHIGH
Load a device driver in to high memory.
LOCK
Lock the hard disk drive.
LOGON
Recovery console command to list installations and enable administrator login.
MAP
Displays the device name of a drive.
MD
Command to create a new directory.
MEM
Display memory on system.
MKDIR
Command to create a new directory.
MODE
Modify the port or display settings.
MORE
Display one page at a time.
MOVE
Move one or more files from one directory to another directory.
MSAV
Early Microsoft Virus scanner.
MSD
Diagnostics utility.
MSCDEX
Utility used to load and provide access to the CD-ROM.
NBTSTAT
Displays protocol statistics and current TCP/IP connections using NBT
NET
Update, fix, or view the network or network settings
NETSH
Configure dynamic and static network information from MS-DOS.
NETSTAT
Display the TCP/IP network protocol statistics and information.
NLSFUNC
Load country specific information.
NSLOOKUP
Look up an IP address of a domain or host on a network.
PATH
View and modify the computers path location.
PATHPING
View and locate locations of network latency.
PAUSE
Command used in batch files to stop the processing of a command.
PING
Test / send information to another network computer or network device.
POPD
Changes to the directory or network path stored by the pushd command.
POWER
Conserve power with computer portables.
PRINT
Prints data to a printer port.
PROMPT
View and change the MS-DOS prompt.
PUSHD
Stores a directory or network path in memory so it can be returned to at any time.
QBASIC
Open the QBasic.
RD
Removes an empty directory.
REN
Renames a file or directory.
RENAME
Renames a file or directory.
RMDIR
Removes an empty directory.
ROUTE
View and configure windows network route tables.
RUNAS
Enables a user to execute a program on another computer.
SCANDISK
Run the scandisk utility.
SCANREG
Scan registry and recover registry from errors.
SET
Change one variable or string to another.
SETLOCAL
Enables local environments to be changed without affecting anything else.
SETVER
Change MS-DOS version to trick older MS-DOS programs.
SHARE
Installs support for file sharing and locking capabilities.
SHIFT
Changes the position of replaceable parameters in a batch program.
SHUTDOWN
Shutdown the computer from the MS-DOS prompt.
SMARTDRV
Create a disk cache in conventional memory or extended memory.
SORT
Sorts the input and displays the output to the screen.
START
Start a separate window in Windows from the MS-DOS prompt.
SUBST
Substitute a folder on your computer for another drive letter.
SWITCHES
Remove add functions from MS-DOS.
SYS
Transfer system files to disk drive.
TELNET
Telnet to another computer / device from the prompt.
TIME
View or modify the system time.
TITLE
Change the title of their MS-DOS window.
TRACERT
Visually view a network packets route across a network.
TREE
View a visual tree of the hard disk drive.
TYPE
Display the contents of a file.
UNDELETE
Undelete a file that has been deleted.
UNFORMAT
Unformat a hard disk drive.
UNLOCK
Unlock a disk drive.
VER
Display the version information.
VERIFY
Enables or disables the feature to determine if files have been written properly.
VOL
Displays the volume information about the designated drive.
XCOPY
Copy multiple files, directories, and/or drives from one location to another.

Unix, Linux and variants

Quick links
Unix ABCsLinux ABCsDOS vs. UnixUnix commandsUnix Top 10 commandsUnix ShortcutsLinux variantsUnix variantsUnix / Linux HistoryUnix / Linux tipsUnix / Linux linksLinux / Unix newsLinux Q&A
Unix ABCs
Unix, which is not an acronym, was developed by some of the members of the Multics team at the bell labs starting in the late 1960's by many of the same people who helped create the C programming language. The Unix today, however, is not just the work of a couple of programmers. Many other organizations, institutes and various other individuals contributed significant additions to the system we now know today.
See additional Unix information and variants and information on the Unix variants page.
Linux ABCs
Developed by Linus Torvalds and further elaborated by a number of developers throughout the world, Linux (lee'nuhks/ or /li'nuks/,_not_/li:'nuhks) is a freely available multitasking and multiuser operating system. From the outset, Linux was placed under General Public License (GPL). The system can be distributed, used and expanded free of charge. In this way, developers have access to all the source codes, thus being able to integrate new functions easily or to find and eliminate programming bugs quickly. Thereby drivers for new adapters (SCSI controller, graphics cards, etc.) can be integrated very rapidly.
See additional Linux information and variants and information on the Linux variants page.

MS-DOS vs. Unix
If you are able to navigate through MS-DOS, you will be able to pick up on the navigation of Linux and Unix; in the below chart we have listed several of the various similarities of DOS and Unix.
MS-DOS
Unix
attrib
chmod
backup
tar
dir
ls
cls
clear
copy
cp
del
rm
deltree
rm -Rrmdir
edit
vipico
format
fdformatmountumount
move / rename
mv
type
less
cd
cdchdir
more < href="http://www.computerhope.com/unix/umore.htm">more file
md
mkdir
win
startx
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Brief overview of UNIX / Linux commands
Below is a listing of each of the Unix / Linux commands currently listed on Computer Hope and a brief explanation of what each of the commands do. This is a full listing which means not all the below commands will work with your distribution and may also not work because of your privileges. Clicking on any of the commands will display additional help and information about that command.
Command
Description
a2p
Creates a Perl script from an awk script.
alias
Create a name for another command or long command string.
ac
Prints statistics about users' connect time.
ar
Maintain portable archive or library.
arch
Display the architecture of the current host.
as
An assembler.
at
Command scheduler.
awk
Awk script processing program.
basename
Deletes any specified prefix from a string.
bash
Command Bourne interpreter
bc
Calculator.
bdiff
Compare large files.
bfs
Editor for large files.
bg
Continues a program running in the background.
biff
Enable / disable incoming mail notifications.
break
Break out of while, for, foreach, or until loop.
bs
Battleship game.
bye
Alias often used for the exit command.
cal
Calendar
calendar
Display appointments and reminders.
cancel
Cancels a print job.
cat
View and/or modify a file.
cc
C compiler.
cd
Change directory.
chdir
Change directory.
checkeq
Language processors to assist in describing equations.
checknr
Check nroff and troff files for any errors.
chfn
Modify your own information or if super user or root modify another users information.
chgrp
Change a groups access to a file or directory.
chkey
Change the secure RPC key pair.
chmod
Change the permission of a file.
chown
Change the ownership of a file.
chsh
Change login shell.
cksum
Display and calculate a CRC for files.
clear
Clears screen.
cls
Alias often used to clear a screen.
cmp
Compare files.
col
Reverse line-feeds filter.
comm
Compare files and select or reject lines that are common.
compress
Compress files on a computer.
continue
Break out of while, for, foreach, or until loop.
copy
Copy files.
cp
Copy files.
cpio
Creates archived CPIO files.
crontab
Create and list files that you wish to run on a regular schedule.
csh
Execute the C shell command interpreter
csplit
Split files based on context.
ctags
Create a tag file for use with ex and vi.
cu
Calls or connects to another Unix system, terminal or non-Unix system.
cut
Cut out selected fields of each line of a file.
date
Tells you the date and time in Unix.
dc
An arbitrary precision arithmetic package.
df
Display the available disk space for each mount.
deroff
Removes nroff/troff, tbl, and eqn constructs.
diff
Displays two files and prints the lines that are different.
dircmp
Lists the different files when comparing directories.
dmesg
Print or control the kernel ring buffer.
dos2unix
Converts text files between DOS and Unix formats.
dpost
Translates files created by troff into PostScript.
du
Tells you how much space a file occupies.
echo
Displays text after echo to the terminal.
ed
Line oriented file editor.
edit
Text editor.
egrep
Search a file for a pattern using full regular expressions.
elm
Program command used to send and receive e-mail.
emacs
Text editor.
enable
Enables / Disables LP printers.
env
Displays environment variables.
eqn
Language processors to assist in describing equations.
ex
Line-editor mode of the vi text editor.
exit
Exit from a program, shell or log you out of a Unix network.
expand
Expand copies of file s.
expr
Evaluate arguments as an expression.
fc
The FC utility lists or edits and re-executes, commands previously entered to an interactive sh.
fg
Continues a stopped job by running it in the foreground
fgrep
Search a file for a fixed-character string.
file
Tells you if the object you are looking at is a file or if it is a directory.
find
Finds one or more files assuming that you know their approximate filenames.
finger
Lists information about the user.
fmt
Simple text formatters.
fold
Filter for folding lines.
for
Shell built-in functions to repeatedly execute action(s) for a selected number of times.
foreach
Shell built-in functions to repeatedly execute action(s) for a selected number of times.
fromdos
Converts text files between DOS and Unix formats.
fsck
Check and repair a Linux file system.
ftp
Enables ftp access to another terminal.
getfacl
Display discretionary file information.
gprof
The gprof utility produces an execution profile of a program.
grep
Finds text within a file.
groupadd
Creates a new group account.
groupdel
Enables a super user or root to remove a group.
groupmod
Enables a super user or root to modify a group.
gunzip
Expand compressed files.
gview
A programmers text editor.
gvim
A programmers text editor.
gzip
Compress files.
halt
Stop the computer.
hash
Remove internal hash table.
hashstat
Display the hash stats.
head
Displays the first ten lines of a file, unless otherwise stated.
help
If computer has online help documentation installed this command will display it.
history
Display the history of commands typed.
hostname
Set or print name of current host system.
id
Shows you the numeric user and group ID on BSD.
ifconfig
Sets up network interfaces.
isalist
Display the native instruction sets executable on this platform.
jobs
List the jobs currently running in the background.
join
Joins command forms together.
keylogin
Decrypt the user's secret key.
kill
Cancels a job.
ksh
Korn shell command interpreter.
ld
Link-editor for object files.
ldd
List dynamic dependencies of executable files or shared objects.
less
Opposite of the more command.
lex
Generate programs for lexical tasks.
link
Calls the link function to create a link to a file.
ln
Creates a link to a file.
lo
Allows you to exit from a program, shell or log you out of a Unix network.
locate
List files in databases that match a pattern.
login
Signs into a new system.
logname
Returns users login name.
logout
Logs out of a system.
lp
Prints a file on System V systems.
lpadmin
Configure the LP print service.
lpc
Line printer control program.
lpq
Lists the status of all the available printers.
lpr
Submits print requests.
lprm
Removes print requests from the print queue.
lpstat
Lists status of the LP print services.
ls
Lists the contents of a directory.
mach
Display the processor type of the current host.
mail
One of the ways that allows you to read/send E-Mail.
mailcompat
Provide SunOS 4.x compatibility for the Solaris mailbox format.
mailx
Mail interactive message processing system.
make
Executes a list of shell commands associated with each target.
man
Display a manual of a command.
mesg
Control if non-root users can send text messages to you.
mkdir
Create a directory.
mkfs
Build a Linux file system, usually a hard disk partition.
more
Displays text one screen at a time.
mount
Disconnects a file systems and remote resources.
mt
Magnetic tape control.
mv
Renames a file or moves it from one directory to another directory.
neqn
Language processors to assist in describing equations.
netstat
Shows network status.
newalias
Install new elm aliases for user and/or system.
newform
Change the format of a text file.
newgrp
Log into a new group.
nice
Invokes a command with an altered scheduling priority.
niscat
Display NIS+ tables and objects.
nischmod
Change access rights on a NIS+ object.
nischown
Change the owner of a NIS+ object.
nischttl
Change the time to live value of a NIS+ object.
nisdefaults
Display NIS+ default values.
nisgrep
Utilities for searching NIS+ tables.
nismatch
Utilities for searching NIS+ tables.
nispasswd
Change NIS+ password information.
nistbladm
NIS+ table administration command.
nohup
Runs a command even if the session is disconnected or the user logs out.
nroff
Formats documents for display or line-printer.
nslookup
Queries a name server for a host or domain lookup.
on
Execute a command on a remote system, but with the local environment.
onintr
Shell built-in functions to respond to (hardware) signals.
optisa
Determine which variant instruction set is optimal to use.
pack
Shrinks file into a compressed file.
pagesize
Display the size of a page of memory in bytes, as returned by getpagesize.
passwd
Allows you to change your password.
paste
Merge corresponding or subsequent lines of files.
pax
Read / write and writes lists of the members of archive files and copy directory hierarchies.
pcat
Compresses file.
perl
Perl is a programming language optimized for scanning arbitrary text files, extracting information from those text files.
pg
Files perusal filters for CRTs.
pgrep
Examine the active processes on the system and reports the process IDs of the processes
pico
Simple and very easy to use text editor in the style of the Pine Composer.
ping
Sends ICMP ECHO_REQUEST packets to network hosts.
pkill
Examine the active processes on the system and reports the process IDs of the processes
poweroff
Stop the computer.
pr
Formats a file to make it look better when printed.
priocntl
Display's or set scheduling parameters of specified process(es)
printf
Write formatted output.
ps
Reports the process status.
pvs
Display the internal version information of dynamic objects within an ELF file.
pwd
Print the current working directory.
quit
Allows you to exit from a program, shell or log you out of a Unix network.
rcp
Copies files from one computer to another computer.
reboot
Stop the computer.
red
Line oriented file editor.
rehash
Recomputes the internal hash table of the contents of directories listed in the path.
remsh
Runs a command on another computer.
repeat
Shell built-in functions to repeatedly execute action(s) for a selected number of times.
rgview
A programmers text editor.
rgvim
A programmers text editor.
rlogin
Establish a remote connection from your terminal to a remote machine.
rm
Deletes a file without confirmation (by default).
rmail
One of the ways that allows you to read/send E-Mail.
rmdir
Deletes a directory.
rn
Reads newsgroups.
rpcinfo
Report RPC information.
rsh
Runs a command on another computer.
rsync
Faster, flexible replacement for rcp.
rview
A programmers text editor.
rvim
A programmers text editor.
s2p
Convert a sed script into a Perl script.
sag
Graphically displays the system activity data stored in a binary data file by a previous sar run.
sar
Displays the activity for the CPU.
script
Records everything printed on your screen.
sdiff
Compares two files, side-by-side.
sed
Allows you to use pre-recorded commands to make changes to text.
sendmail
Sends mail over the Internet.
set
Set the value of an environment variable.
setenv
Set the value of an environment variable.
setfacl
Modify the Access Control List (ACL) for a file or files.
settime
Change file access and modification time.
sftp
Secure file transfer program.
sh
Runs or processes jobs through the Bourne shell.
shred
Delete a file securely, first overwriting it to hide its contents.
shutdown
Turn off the computer immediately or at a specified time.
sleep
Waits a x amount of seconds.
slogin
OpenSSH SSH client (remote login program).
sort
Sorts the lines in a text file.
spell
Looks through a text file and reports any words that it finds in the text file that are not in the dictionary.
split
Split a file into pieces.
stat
Display file or filesystem status.
stop
Control process execution.
strip
Discard symbols from object files.
stty
Sets options for your terminal.
su
Become super user or another user.
sysinfo
Get and set system information strings.
sysklogd
Linux system logging utilities.
tabs
Set tabs on a terminal.
tail
Delivers the last part of the file.
talk
Talk with other logged in users.
tac
Concatenate and print files in reverse.
tar
Create tape archives and add or extract files.
tbl
Preprocessor for formatting tables for nroff or troff.
tcopy
Copy a magnetic tape.
tee
Read from an input and write to a standard output or file.
telnet
Uses the telnet protocol to connect to another remote computer.
time
Used to time a simple command.
timex
The timex command times a command; reports process data and system activity.
todos
Converts text files between DOS and Unix formats.
top
Display Linux tasks.
touch
Change file access and modification time.
tput
Initialize a terminal or query terminfo database.
tr
Translate characters.
traceroute
Print the route packets take to network host.
troff
Typeset or format documents.
ul
Reads the named filenames or terminal and does underlining.
umask
Get or set the file mode creation mask.
unalias
Remove an alias.
unhash
Remove internal hash table.
uname
Print name of current system.
uncompress
Uncompressed compressed files.
uniq
Report or filter out repeated lines in a file.
unmount
Crates a file systems and remote resources.
unpack
Expands a compressed file.
untar
Create tape archives and add or extract files.
until
Execute a set of actions while/until conditions are evaluated TRUE.
useradd
Create a new user or updates default new user information.
userdel
Remove a users account.
usermod
Modify a users account.
vacation
Reply to mail automatically.
vedit
Screen-oriented (visual) display editor based on ex.
vgrind
Grind nice program listings
vi
Screen-oriented (visual) display editor based on ex.
vim
A programmers text editor.
view
A programmers text editor.
wait
Await process completion.
wc
Displays a count of lines, words, and characters in a file
whereis
Locate a binary, source, and manual page files for a command.
while
Repetitively execute a set of actions while/until conditions are evaluated TRUE.
which
Locate a command.
who
Displays who is on the system.
whois
Internet user name directory service.
write
Send a message to another user.
X
Execute the X windows system.
xfd
Display all the characters in an X font.
xlsfonts
Server font list displayer for X.
xset
User preference utility for X.
xterm
Terminal emulator for X.
xrdb
X server resource database utility.
yacc
Short for yet another compiler-compiler, yacc is a compiler.
yes
Repeatedly output a line with all specified STRING(s), or 'y'.
yppasswd
Changes network password in the NIS database.
zcat
Compress files.