cpu

CPU

CPU-Central Processing Unit, The CPU is the brain of the computer. Sometimes referred to simply as the processor or central processor, the CPU is where most calculations take place. In terms of computing power, the CPU- is the most important element of a computer system.

The two biggest manufacturers of PC CPU chips are those made by Intel and AM[) other CPU makers include Motorola, Via, and Cyrix

Central Processing Unit (The Brain of the Computer)

Two typical components of a CPU are:

The arithmetic logic unit (ALU), which performs arithmetic and logical operations The control unit, which extracts instructions from memory and decodes and executes them, is calling on the ALU when necessary.

CPU Terminology

Clock speed: Given in megahertz (MHz) or higher (GHz), the clock speed determines how many instructions per second the processor can execute. Also called clock rate, the speed at which a microprocessor executes instructions. Every computer contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks (or clock cycles) to execute each instruction. The faster the clock. the more instructions the CPU can execute per second. Clock speeds are expressed in megahertz (MHz), 1 MHz being equal to 1 million cycles per second. 1 MHz = 1 million clock cycle 1 GHz =1 billion clock cycle

Bus Speed The speeds in which a processor can send data in a pathway. There measured in the following speeds listed below: 33MHz, 66MHz, 100MHz, 133MHz, 166MHz, 200MHz, 233MHz, 266JVlHz, 333MHz, 400MHz, 800MHz, 1600MHz, 3200MHz and 6400MHz

Bus Width 32 vs. 64 bit

Address Bus: Refers to the wires that carry specific addresses to and from the processor .

. Cache: Frequently stored memory, most older CPU's have anL1 internal cache built in with an L2 external cache support chips. Newer CPU's like the pentium IV have and L1 and L2 cache built in with a L3 cache Cache is a very fast memory that is used to hold data and instructions

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VRM (Voltage Regulator Mode) Is the circuitry that sends standard level voltage to the CPU

RISC vs. CISC Reduce Instruction Set Computing vs. Complex Instruction Set Computing

Math Co Processor Ability of a CPU to perform math functions and advance calculations

Cooling Mechanism Devices use to cool a CPU (FAN, Heat Sink and Liquid Cooling) also thermal paste

Overclocking Making a CPU run faster than it should

Front Side vs. Backside Bus How the CPU communicates with the memory and the cache

Hyperthreading Is a technology developed by Intel that acts as two processors

Multicore or Dual Core, Triple Core or Quad Core Has the capability to act as separate processor in the same CPU

Instruction set: The set of instructions that the microprocessor can execute .

. Bandwidth: The number of bits processed in a single instruction.

Pipelining - Allows a new instruction to start processing while a current instruction is still being processed.

Branch Prediction ~ A technique that attempts to infer the proper address of the next instruction while knowing only the current one.

Superscalar execution - Adding one more execution engine in a CPU

Dynamic execution - Allows the CPU to evaluate the programs's flow and choose the best order in which to process the instructions

Registers: Temporary storage areas that hold data before and after processing by the ALU. It similar to a work table use by the CPU

Computer Packages, Slots and Sockets

SEC- Single Edge Cartridge a new CPU package thatis slightly bigger with a built in fan that goes into a SLOT 1 or SLOT A socket.

AMD Athlon SEC

SLOT 1 - The form factor for Intel's Pentium II processors The Slot 1 package replaces the Socket 7 and Socket 8 form factors used by previous Pentium processors. Slot 1 is a 242-contact daughter card slot that accepts a microprocessor packaged as a Single Edge Contact (SEC) cartridge. A motherboard can have one or two Slot 1s. Some Pentium III and Celeron also use SLOT 1.

SLOT A - Similar to Intel's Slot 1 but used for AMD Athlons

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SLOT 2 Slot 2 is a 330-contact use by Intel Pentium II, III XEON found mostly on server computers

PGA-Short for pin grid array, a type of chip package in which the connecting pins is located on the bottom in concentric squares. PGA chips are particularly good for chips that have many pins, such as modern microprocessors. They go into different types of CPU sockets.

Different types of PGA

SPGA: Staggered Pin Grid Array BCPGA: Ball Chip Pin Grid Array FCPGA: Flip Chip Pin Grid Array CPGA: Ceramic Pin Grid Array BPGA-Ball Pin Grid Array

ZIF - Zero insertion force, a chip socket that allows you to insert and remove a chip without special tools.

Socket - A female connector where a CPU connects

Note * PGA and LGA fits into a socket and SEC packages fits into a slot

other CPU packages include the following:

PAC - Pin Array Cartridge (Use in Itanium CPU's)

LGA - Land Grid Array (Newer technology replacing PGA) Use grid instead of pins

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Newer CPU CHART

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Older CPU CHART

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Intel CPU Chart ....... Ma.~~le..ia.ck~::;lap'5~1,t ....c§!:R.,. 9CPJ'DD1tAffl

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AMD CPU Chart ,

CPU Troubleshooting

Problems with heat (cooling mechanism FAN, Heat Sink and Liquid Cooling)

5 Minute shut down (CPU is overheating)

Listen for fan for breakdown and weird unusual noises

Computer won't start ,­

Computer is acting erratic

Keep air case tight

CPU Compatibility (look at chart)

Overclocking (make sure you have the proper cooling mechanism to support this or you will damage your CPU)

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~ When installing CPU be careful don't bend or break pins ,

Match PGA to Socket (ZIF) and SEC to Slot

ZIF (Zero Insertion Force)

,;-Match Pin 1to the socket or look for notches when installing CPU .:.~~~~~ . .

,A,,'oid ESD by grounding one's self 'J~" .c-»: " .

Make sure CPU use the proper voltages

CPU Installation

CPU package must match pin 1 with CPU Socket

Put thermal compound on CPU and install proper cooling mechanism (Fan, Heat Sink or Liquid)

CPU SEC slide in CPU slot and install proper cooling mechanism (Fan, Heat Sink or Liquid)

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MEMORY

·1 nternal storage areas in the computer The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for "physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk. Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.

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\Memory Manufacturers Corsair, Kingston, Rambus; Crucial, Samsung, PNY, Micron

Memory Terminology

. Memory speed - measured in nanoseconds, this is the time to access data that is stored in memory ···the lower the nanoseconds the faster the memory (2ns-80ns)

~ '.".". .. Parity -'A simple error checking method use in memory correction

ECC-Error correction code use in memory correction for newer computers

I\/Iemory Banks - A socket where memory is installed Example 4 banks will have 8MB of memory each for a total of 32MB

There are several different types of memory:

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DRAM PACKAGES

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DRAM Types & Uses

$0 OIMM (72,100,144; 200, 2(.4pin)

------ LaptopsI (SDMMer DlJRyDJtitM)MicroDIMM

DDR2oS0RAM(172,214pin) DDR3-S0RAM

se-ptn SIMrlll· FPMor EI10 . (Fast Page Modepr£00)

72-pinSIMM EDO orSDRAM

(ExtendedD(!ta Out)·

,168-pin DIMM "SDRAM .(Synchronous Dynamic RAM) .

184-pin DIMM ..DDR-SDRAM (Dt>lIbJeData RateSDBAM)

240-pin DIMM DOR2-SDRAM (DollbleDafa Rate 2SDRAM)

184-pin RIMM .. RORAM .(RambUs Dynamic RAM)

232-pin RIMM .RDRAM (nambUS Dynamic RAM)'

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ROM or Read Only Memory, Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. It is non-volatile which means once you turn off the computer the information is still there.

PROM, short for programmable read-only memory A PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike RAM, PROM's retain their contents when the computer is turned off. The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.

EPROM (erasable prcqrarnrnable read-only memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM issimilar to a PROM, but requires only electricity to be erased.

EEPROM- Acronym for electrically erasable programmable read-only memory ..Pronounced double-ee­prom or e-e-prom, an EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM. EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster.

RAM (Random Access Memory) is a temporary (Volatile) storage area utilized by the CPU. Before a program can be ran the program is loaded into the memory which allows the CPU direct access to the program.

2 Types of RAM

SRAM Short for static random access memory, and pronounced ess-ram. SRAM is a type of memory that is faster and more reliable than the more common DRAM (dynamic RAM). The term static is derived from the fact that it doesn't need to be refreshed like dynamic RAM. . SRAIVI is often used only as a memory cache usually found in the CPU (Lt, L2 and L3 Cache)

DRAM stands for dynamic random access memory, a type of memory used in most personal computers.

Types of DRAM Packages and DRAM Memory

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LAPTOP MEMORY

(72,144,200) SO-DIMM

SO-DIMM Short for Small Outline DIMM, a small version of a DIMM used commonly in notebook computers. 72 supports 32bit and 144 and 200 SO-DIMM pins supports a full 64-bit transfer.

(144,172) Micro-DIMM

Micro-DIMM Short for Micro Dual Inline Memory Module, a competing memory used on laptops, mostly supports 144 and 172 pins.

SIMM Acronym for single in-line memory module, a small circuit board that can hold a group of memory chips. Typically, SIMM's holds up 8 (on Macintoshes) or 9 (on PCs) RAM chips. On PCs, the ninth chip is often used for parity error checking. Unlike memory chips, SIMM's is measured in bytes rather than bits. SIMM's is easier to install than individual memory chips. A SIMM is either 30 or 72 pins.

30 piri"SIMM (Usually FPM orEDORAM)

FPM RAM Short for Fast Page Mode RAM, a type of Dynamic RAM (DRAM) that allows faster access to data in the same row or page. Page-mode memory works by eliminating the need for a row address if data is located in the row previously accessed. It is sometimes called page mode memory.

72 pin SIMM (EDO RAM)

EDO DRAM Short for Extended Data Output Dynamic Random Access Memory, a type of DRAM that is faster than conventional DRAM. Unlike conventional DRAM which can only access one block of data at a time, EDO RAM can start fetching the next block of memory at the same time that it sends the previous block to the CPU.

DIMM Short for dual in-line memory module, a small circuit board that holds memory chips. A single in­line memory module (SIMM) has a 32-bit path to the memory chips whereas a DIMM has 64-bit path. Because the Pentium processor requires a 64-bit path to memory, you need to install SIMM's two at a time. With DIMM's, you can install memory one DIMM at a time. A DIMM contains 168 pins.

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168 pin D1MM (SDRAM)

SDRAM Short for Synchronous DRAM, a new type of DRAM that can run at much higher clock speeds than conventional memory. SDRAM actually synchronizes itself with the CPU's bus and is capable of running at 133 MHz, about three times faster than conventional FPM RAM, and about twice as fast EDO DRAM. SDRAM is replacing EDO DRAM in many newer computers SDRAM delivers data in high speed burst

184 pin DIMM (DDR-SDRAM)

DDR SDRAM Short for Double Data Rate-Synchronous DRAM, a type of SDRAM that supports data transfers on both edges of each clock cycle, effectively doubling the memory chip's data throughput. DDR-SDRAM is also called SDRAM II.

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240 DIMM(DDR2~S[)RAM)

DDR2-SDRAM Short for Double Data Rate Synchronous DRAM 2 is a type of DDR that supports higher's speeds than it's predecessor DDR SDRAM

24'0 DIMM (DDR3-SDRAM)

DDR3-SDRAM Short for Double Data Rate Synchronous DRAM 3 is the newest type of DDRthat supports the fastest speed of all the SDRAM memory

]184 pin RIMM (RDRAM)

RIMM Rambus Inline Memory Module, The memory module used with RDRAM chips. It is similar to a DIMM package but uses different pin settings. Rambus trademarked the term RIMM as an entire word. It is the term used for a module using Rambus technology. It is sometimes incorrectly used as an acronym

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I for Rambus Inline Memory Module. A RIMM contains 184 or 232pins. Note must use all sockets in RIMM installation or use C_RIMM to terminate banks

. 232 pin RIMM (RORAM)

RDRAM Short for Rambus DRAM, a type of memory (DRAM) developed by Rambus, Inc. In 1997, Intel announced that it would license the Rambus technology for use on its future motherboards, thus making it the likely de facto standard for memory architectures.

CLICK HERE for a picture and more information on RIMM Installation

SIMM and DIMM Sockets

SORAM Chart

EJ .168 OIMM (SORAM)

ClockModuleModule Cycles Per EJ BusBus. . WidthIP SpeedStandard Format clockType (MHz) Speed (Bytes)

IPC66 II SDR DIMM \ \ 10ns 66 1 1\66 1\811 11

IPC100 I[WR DIMM \ \ 8ns \ \ 100 11 1 1\100 1\8

IPC133 II SDR DIMM 117ns 133 1 133 8 11 11 11 11

Transfer Rate (MB/s)

1\533 I 1\800 I 11 1,066 I

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IRIMM 1600 II RIMM-16 II PC800 400 2 800 2 11 1,600 11 11 11 11 I

!RIMM 2100 II RIMM-16 I [PC1066 11 533 2 11 1,066 2 11 2,133

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600 2I RIMM 2400 )IRIMM-16 II PC1200 11 11 1,200 2 11 2,400 11 11

I RIMM 3200 II RIMM-32 II PC800 400 2 800 2 11 3,200 11 11 11 11 I

I RIMM 4200 II RIMM-32 II PC1066 11 533 2 11 1,066 2 11 4,266 11 11

I RIMM 4800 II RIMM-32 II PC1200 11 600 2 11 1,200 2 11 4,800 11 11

RAM Desktop Installation

. Note RAM Memory Sticks come in the following sizes

8MB, 16MB, 32MB, 64MB, 128MB, 256MB, 512MB, 1GB, 2GB, 4GB and 8GB

SIMM - Single Inline Memory Module Installation (30 or 72 pin)

1. Place SIMMina 45d~gree angle, push it upright to lock with the corresponding notch on the sides 2. Must be installed in same pairs . 3. Must populate first two slots of the SIMM sockets in order for it to work

DIMM - Duallnline Memory Module Installation (168,184 or 240 pin)

1. The first thing you do is open the plastic retaining clips on each side of slots you are going to use. 2. Aiign the cut-out on the module oin connector VJit~1 the engaaina pin on the slot 3. Holding the module upright press down both ends. . ~ v

4. When the module is correctly seated, retaining clips should lock automatically. 5. DIMM's can be installed as a single pair (unless it states Dual Channel then you must install it in pairs)

RIMM - Rambus Inline Memory Module Installation (184 or 232 pin)

1: The first thing you do is open the plastic retaining clips on each side of slots you are going to use. 2. Align the cut-out on the module pin connector with the engaging pin on the slot 3. Holding the module upright press down both ends. 4. When the module is correctly seated, retaining clips should lock automatically. 5. Must populate all RIMM slots available 3. If not unpopulated slots must use CRIMM's (Continuity Rambus Inline Memory Module)

Memory Troubleshooting

MEMORY (when installing use a ground strap because of ESD) ESD (low and high humidity) Mixed Memory usually equals fried memory Parity Errors or ECC Errors (Memory correction errors) SIMMS must be installed in pairs RIMMS must be all installed in all slots or CRIMM's must be needed in unvacated RIMM slots General Protection Fault (memory overwrite) Not enough memory (computer is slow) NMI -Non Maskable Interrupt will cause BSOD (Blue Screen of Death) Multiple beeps when booting up check that memory is properly installed and working

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No Video (Reseat memory) Memory speeds set in BIOS/CMOS Setup Virtual Memory (Page fault) Chip Creep - Thermal expansion and contraction

Special Thanks te Rambus, Cesair, PNY, Viking, American Megatrends, Centen, Samsung, Crucial and Micron

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We all spend an awful lot of time sat in front of computers. Whether we're gaming or working, we are at the mercy of what many would argue is the most important element of any system - the monitor.

A well-defined monitor can make using a system a pleasure. Likewise, being forced to squint at a 15" CRT at 60Hz can make us weep in pain and long for a nice LCD to while away our hours CIt. A good display makes all the difference.

Monitors are widely used and rarely understood Sure, you know that the difference between LCD and CRT is that one is flat and one is massive and heavy. But do you really understand the technology that goes into these things?

In this article, we're going to investigate how CRTs and LCOs work, and also examine some of the issues pertaining to monitors, such as Refresh Rate and Vsync as well as looking into our crystal ball to see the future of displays.

For a primer on resolutions, you might like to check outour previous article here.

The Basics

So let's start with the easy stuff. The picture that appears on your monitor cernes from the graphics card in your computer, and the job of the graphics card is to render the picture suitable for the monitor. A wired output runs from the graphics card to the monitor.

But you knew that already.

Both the graphics card and monitor adhere to the same set of specifications; so that they can happily talk to each other. The standards are set out by VESA. which defines things like how rncriitors identify themselves to the computer. . '

crrrs CRT stands for Cathode Ray Tube, and is descriptive of the technology inside that chunky monitor you might have on your desk.

CRTs receive their picture throuqh an analogue cable,· and that signal is decoded by the display controller, which handles the internal components of the monitor - think 'of it as the mini-CPU for the monitor.

CRTs have a distinctive funnel shape. At the very back of a monitor is an electron gun. The electron gun fires electrons towards the front through a vacuum which exists in the tube of the monitor. The gun can also be referred to as a cathode - hence the electrons fired foward are called Cathode Rays.

These rays correspond to to the red, green and blue channels of the display and video card.

At the neck of the funnel-shaped monitor is an anode, which is magnetised according to instructions from the display controller. As electrons pass the anode, they are shunted or pulled in one direction or the other depending on how magnetic the anode is at that time. This moves the electrons towards the correct part of the screen.

RGB phosphors

Shadowmask or Aperture Grill

Magnetic anodes

Cathoderay gun

The electrons pass through a mesh, and this mesh defines the individual pixels and resolution on the screen. Electrons that pass through the mesh then hit the phosphor coating which is on the inside of the glass screen. When the particles hit the phosphor, they immediately light up - causing the light to shine through the front of the monitor, thus making up the picture on the screen. There are three differently coloured phosphours for each pixel (known as phosphor triads), and depending on which phosphor the electron hits, that's which colour the pixel will light up.

Differences in components

Different monitors differ in quality, and this is often dependent on the technology and components used internally.

, Some CRT monitors use a single electron gun at the rear of the monitor to produce the electrons that will become the red, green and blue electron rays. However, higher quality monitors have an individual gun for each, which can increase picture quality.

'The metal used for the mesh at the front of the monitor will also affect quality. Electrons also produce ions because of imperfections in the vacuum, and these electrons are destructive to image quality if they hit the phosphor. Consequently, meshes are made of relatively thick metal to prevent phosphor damage. However, in better quality monitors, a thinner, yet tougher metal alloy is used for the mesh. Because it's thinner, it means more light can get through, making for increased brightness and higher contrast.

Aperture Grille v Shadow Mask

Each CRT has a sheet of metal at the front of the monitor which (partly) defines the pixels on the screen. Shadow mask is an older technology, and is literally a piece of metal with millions of holes in it which allow the different cathode rays through to hit the phosphour. Because a shadow mask covers the whole back of the screen, protecting the phosphor from stray ions, it also limits the strength of the rays, reducing the brightness of the monitor.

Aperture grille is a newer technology which defines the gaps through which electrons pass using a mesh of wires rather than a sheet with holes in. Whereas a shadow mask is made of circular holes, the grill is made of vertical slots. Because it is by its nature thinner, it allows for brighter displays. However, the grill is fragile and prone to being knocked around. The grill is therefore strapped to the monitor using stiff horizontal wires - this is what causes the distinctive pair of lines' across high-end aperture grille monitors.

Invar mask is a variant of shadow mask, and uses a thinner, stronger metal to form the mask, allowing for better image quality whilst remaining cheaper than aperture grill to produce.

Sony's Trinitron brand and Mitsubishi's Diamondtron brand are both variants of Aperture grill.

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Shadow mask andAperlure Grill

Dot pitch and resolution

Each pixel on the CRT screen is defined by lighting up combinations of the red, blue and green phosphors that make up the pixel. With a varying strength of electron gun operating on each phosphor, different colours are produced ­with red, blue and green all fired on maximum strength, that means bright white is produced.

Dot pitch is measured on most monitors as the distance, diagonally, between two phosphors of the same colour. However, some manufacturers quote dot pitch on monitors as the horizontal distance between phosphors, which can make them appear better specified, on paper, than perhaps they are.

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Dotpitch

Dot pitch combined with viewable image area defines the maximum resolution of the screen. For example, if you have a 21" monitor with a viewable area of 401mm x 298mm, and a dot pitch of 0.26mm, you will have a CRT capable of displaying a maximum resolution of 1758 horizontally. How so?

Well, if we take 1 as the diagonal dot pitch, Pythagorus dictates that the horizontal dot pitch (ie the gap between pixels as rendered horizontally by the graphics card) will be 0.87. 0.26 diagonal dot pitch multiplied by 0.87 makes for a diagonal equivalent pitch of 0.228 horizontally. 401mm horizontal viewable screen area multiplied by 0.228 is 1758, hence a maximum of 1758 pixels are usable on the screen.

LCD

Flat panel monitors are a relatively recent product to enter the computer market. The clue to LCD technology is in the . name - crystals that are in liquid form. Because they are in a liquid form they are easily manipulable, and this allows us to play with the way that light interacts with them. If you have a flat panel in front of you, try just pressing gently on the surface - you can see the crystals move around and alter the picture .

. LCD panels are fairly simple to understand. The signal comes in and, as with a CRT, the signal from the video controller is decoded and understood by a display controller on the monitor itself. The controller has two things to control - the electrics of the pixels and the light source.

The actual image on a TFT is made up of a matrix of pixels. Unlike with CRTs, there's no complex equation of dot pitch and image area to try and calculate - the native resolution of the monitor is simply the number of pixels contained in the matrix. If it's a 17" monitor, chances are there are 1280 pixels in the matrix horizontally, and 1024 vertically.

Backlight source

Liquid crystals

Perspective view

Each pixel is made up of three sub-pixels, which have red, green and blue filters in front of them, just as each pixel on a CRT has RGB phosphors. The subpixels are made up of a group of liquid crystal molecules. These molecules are suspended between transparent electrodes and are mashed between two polarising filters.

The two filters are exact opposites of each other. As the light from the light source behind the first filter comes in, the filter effectively whites it out - which means that if it was to pass through the liquid crystals with no interaction, the filter on the other side would polarise it back to black, leaving no colour being emitted. In fact, alternate current ­leaving the crystals 'dead in the water' - is how black is created on a panel.

However, if the electrodes apply current to the liquid crystals they twist and change the way that the light is passed through, altering its polarisation and this then results in the correct colour coming out of the second polarising filter and being displayed to the user.

The backlight itself is a cold cathode. Depending on how expensive the display is, there will be either a single cathode at the top, or one at the top and one at the bottom, or two at the top and two at the bottom for optimum brightness and clarity. These cathodes are diffused through a layer of plastic and then through multiple layers of diffusing material of the kind you might find on a flashgun diffuser for photography.

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matrix

Polarising filters

Exploded view of LCD from side on

Contrast ratio

One of the major factors affecting a TFT is the amount of contrast it has. Traditionally, the contrast is lower than on CRT monitors, allowing for less differentiation between blacks and whites - and meaning that blacks are often ill­defined.

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This is the reason that many gamers still prefer CRTs for games like Doom 3 and FEAR, which have an awful lot of black in them.

. Put simply, the contrast ratio of a display is the ratio of the brightest possible white value compared to the darkest possible black value. Most desktop TFT monitors have a contrast ratio of between 300: 1 and 600:1 while a typical LCD 1V will raise that to between 800:1 and 1200:1.

Because the light of the backlight is so bright, the second polarising filter is not able to keep out all of the light when the display calls for black, and this means that blacks can sometimes appear a little more grey. Alternatively, if you turn the backlight brightness down to get pure blacks, this drags the brightness of bright white down. The greater the contrast ratio, the greater the difference between black and white you can maintain and the better quality the display.

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For more details on contrast and brightness, check out our article on the Brightside display.

Bit depth

One of the most overlooked features of LCD panels is the colour depth of the panel. To achieve the ultra-low response times that companies often want to sell, colour depth is sometimes compromised by optimising panels for speed rather than quality.

Good quality panels use 8 bits of colour per RGB channel, resulting in 16.7m colours displayable. However, on many modern TFT panels, only 6 bits per channel are used, resulting in just over 16m colours with the rest being dithered, or 'faked', by algorithms.

If you're doing image editing, you will notice the dithering and if you want a high quality panel, you should look for one that's 8-bit. Professional quality panels will use 10-bit colour, and the newer ATI Radeon cards will support that output.

Don't confuse 8-bit colour with 32-bit colour on the desktop, and think that LCD panels aren't utilising the full potential of your awesome rig. 32-bit colour is actually 8 bits of alpha channel and then 8-bit RGB - the same as in your monitor. Good LCD screens can handle everything that the video card can put out.

Refresh rates

60Hz, 100Hz, Vsync... how do all these terms inter-relafe?

On a CRT, the refresh rate is how many times, per second, the display is drawn - i.e. how many times the electron guns are told to fire by the video source. The refresh rate on a monitor is limited by how fast the guns can fire - more expensive guns can obviously fire faster. The refresh rate is also limited by the resolution, because the higher the number of vertical lines to refresh, the longer it takes the guns to refresh them all.

We all know from experience that a higher refresh rate makes for a better image that has less flicker, but do we know why? The phosphors in a CRT illuminate when hit with electrons, but begin to fade as soon as the energy from the electron is used up. To keep the phosphor illuminated requires a constant stream of electrons. If they're not coming in fast enough, the phospor will visbly fade then light up again - causing that horrendous 60Hz flicker we all know and love, which is especially visible on high resolution screens with lots of vertical lines to scan. 60Hz is more tolerable on a lower resolution screen where there are less lines to scan.

On a CRT monitor with a resolution of 1600x1200 or above, 100Hz is ideal to keep all the lines supplied with enough electrons to stop the phosphors fading and flicker occurring.

Refresh and Response on LCDs

All of this doesn't really apply to LCOs. The pixels and subpixels in LCD panels don't fade as phosphor does, since the light from the backlight is constant and the current from the electrodes is constant, meaning that light is passed from the pixels for as long as the display controller tells it to. However, LCOs are nominally set up to report a 60Hz refresh back to the video controller, which often requires at least some value to work to.

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What does matter on a LCD, however, is the response time. This is not the same as a refresh rate. Refresh rate time is the measurement of how many frames can be displayed per second. For an LCD, response time refers to how quickly a liquid crystal can twist, then untwist to either pass or block the light of each pixel. The faster the crystals can react, the faster the motion that can be displayed on screen.

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This is why a low response time is essential for applications like movies and games to be watch able without ghosting. Ghosting is the remnants of the old frame image 'below' the new frame image due to the fact that not all the crystals have updated with the new frame in time to display it.

Any response time below 16ms is fast enough for the eye to perceive full motion, and today's displays of 8, 4 and even 2 milliseconds will all provide a great Viewing experience.

Vsync

This is an option used in games to present optimum image quality. When Vsync ts enabled, the video controller sends the output to the monitor in line with the refresh rate of the monitor - so 60 frames a second are sent to the monitor if the monitor has a 60Hz refresh rate. Where 80 frames are sent to a 60Hz monitor, the monitor will spend some of its time trying to draw a new frame when the old frame hasn't finished being displayed across all of the monitor. This results in the image 'tearing' that you see occur.

Obviously, Vsync limits frame rate which most people would see as detrimental to a gaming experience. However, with SUitably powerful graphics hardware, a constant minimum frame rate of 60FPS coupled with Vsync makes for optimum image quality and gameplay.

Disassembling a LCD monitor

To give you a further insight into the technology inside flat screens, we thought we'd take one apart and see what was inside. Many thanks to the guys at Viewsonic for giving us a dead unit from their stock to mutilate.

Here's the stock unit: a standard 17" monitor, 1280x1024 resolution. The back is held on with a couple of screws in the stand, a couple at the bottom of the monitor and then plastic bezel clips between the front and back plastic halves. .

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With the back off, you can see the display controller. The circuitry here has cables going off it to the power unit, to the cathodes that light the display and to the actual electrodes controlling the liquid crystals.

Here you can see the power circuitry on the left, and the circuit that handles the front panel buttons on the right.

With acouple more screws removed on the side,this back panel circuitry is removed and we are left with the actual flat panel. Are we going to stop here?

NexLup: unscrew the metal backing and prise it off - not an easy task, these things are put together pretty solidly.

Here you .can see we're getting to the guts of the panel. The big white board is the major part of the diffusing mechanism, with multiple layers of thing plastic in front and behind it to provide extra relectivity and diffusion.

Here are the actual cathodes that are attached to the display on the top and the bottom. This particular model has dual-dual cathodes for maximum brightness.

With the diffusing material and backlight pulled away, we're left with the panel. Attached to the bottom of the panel is a secondary circuit board that controls the electrodes used to manipulate the liquid crystals.

Here you can see the polarising filters that are on each side of the display. They are incredibly sticky and rather hard to peel off! We managed to prise back a couple of corners. Of course, they look pretty similar to the eye but allow light 'waving' in different directions to pass through.

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~ If you look closely at the panel here, you can just about make out the individual pixels that make up the display matrix.

t Future technology in LeDs

.,:, What does the future hold for display technology? " ..~.~ .

. ":;" . Arguably, there is not much of a future at all for CRT technology. As LCDs get better and better, with faster response ,~3:.1jmes, better contrast and higher resolutions, the uses for the analogue output it provides will become fewer, given 't, ~::the convenience of the form factor of LCD displays.

',~/t:,:philipsand other companies have come up with technology to create flatter CRTs, which occupy less than half the space of a traditional CRT of any given specification, but even these look bulky compared to today's svelte LCD designs.

Connections: The first area that LCDs will evolve in is through different connector types, VGA and DVI are, effectively, connections that are becoming obsolete. The new standards coming in are HDMI and UDI, which we have written about previously. These standards should allow for better quality connections with more featureset, such as

, the ability to carry audio and video along a single cable.

LED backlighting: We've seen that LCDs are currently backlit by a number of cold cathodes above and below the screen. New technology replaces these heat-producing, power-intensive cathodes with cooler, more efficient LEDs. Laptops using LED backlighting are now starting to come into the mainstream, with the Sony TX2 sporting a 7 hour battery life thanks.to the efficiency of its backlight LCD monitors are now also beginning to approach reference CRT quality thanks to the technology - check out this review of the NEC Spectraview for more details,

The Sony TX2 laptop with LED backlight Better panel types: Currently, the vast majority of monitors on the market are sold with Twisted Nematic (TN) LCD panels. This type of LCD panel usually has a great response time, but the colour range and viewing angle can often be limited.

Multi-domain Vertical Alignment (MVA) panels have fast response time, wider viewing angles and a much better contrast, resulting in a better picture overall. However, it is a more expensive technology. As costs fall, however, MVA panels could deliver better image quality to TFT monitors.

Leaping,ahead

If we were to leap into the future, we would see some fairly hefty transitions in display technology. , . .

SEDs: Surface-conduction Electron-emitter displays are being touted asa replacement for LCD panels.SEDs use a phosphor coating, like CRTs, that is charged with electrodes - only rather than from behind through a vacuum, like a CRT, the electrodes are within the matrix of pixels, like with a LCD. They are said to produce better images than LCD with a cost that will eventually be lower. Prototypes have already been shown off by companies like Toshiba and displays are expected to be available on the market in 2007. However, some remain sceptical about the technology and manufacturing problems and costs that are yet to be overcome.

Curved displays: At the Consumer Electronics Show in Las Vegas this year, Bill Gates showed off a number of concept displays that he believed would be on the market within the next 10 years. Perhaps the most awesome of these was a field-of-view curved display. Around the size of two 24" panels 'sewn' together, the curved display sat on the desktop and allowed for things on the monitor to be seen in the peripheral vision outside of our 90 degree standard view. Imagine gaming on one ofthosel Since the display is curved; wenaveto-iinaqe it was an OLEO display, which can be produced in that way.

A picture of the desk-sized display Bill showed at CES (courtesy www.tsr.ch)

Table displays: Bill also showed off a concept display built into a coffee table, where the surface of the table becomes the screen when a device, like a PDA, is placed on top of it. This could bring a 'big-screen' Interface to

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POAs and Gates suggested that they'd be used at.airports and other places where keyboard-mouse-monitor access : was limited.

OLEO: Short for Organic Light Emitting Diode, OLEO could well replace LED as the display of choice over coming years. OLEO has similarities to SED technology, in that the lighting material is an organic substrate. When current is applied, it glows. However, rather than the material being on the panel, it is within the LED itself, meaning that LEOs can be coloured as required to emit the correct light - with no RGB sub-pixels needed. Because the electricity can operate directly on the substrate, you don't need to have a backlight - this saves on power and space.

OLEO is already starting to make its way into the market, such as with this BenQ phone.

POST (POWER ON SELF-TEST)

POST

POST or Power On Self-Test 1. Power Supply turned on sends electrical signals to CPU 2. CPU wakes up and runs and invokes the BIOS boot up program 3. CPU sends signals to system bus 4. CPU checks system timer or real time clock 5. POST test memory 6. Memory amount is run and checked 7. CPU verifies keyboard ..-; ":..'".

8. POST send signals to floppy and hard disk 9. POST compares results with CMOS setup 10. POST checks BYOB and now is ready to boot Lip as

PC hierarchy

Hardware BIOS Operating System Drivers Applications

Generic error codes Note that different BIOS manufacturers generate different error codes you must use the guidelines provided by these manufacturer to troubleshoot your computer, provided below are generic error-codes provided by a typical computer.

POST visual Errors This will show up on your computer as visual error codes

Error Range Component with Error

100-199 Motherboard 200-299 RAM or Memory 300-399 Keyboard 400-499 Video Mono 500-599Video Color 600-699 Floppy Drive 700-799 Math Co-Processor 900-999 LPT1 1000-1099 LPT2 1100-1199 COM 1 1200-1299 COM 2 17xx Hard Disk Controller 3xxx NIC 86xx Mouse

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POST audio Errors Your will hearthese error codes when your computer boots up

Error Code Faulty Component

1 Short Beep None (Normal Boot) 2 Short Beeps POST error None Speaker broken, turned off, Power Supply or Motherboard Non Stop Beep Power Supply or Motherboard Non-Stop short beeps Power Supply, Motherboard or Keyboard with something stuck or something on top of it 1 short beep, nothing on screen video card failure 1 short beep, video present, but system won't boot Bad floppy drive, cable or controller 1 Long Beep and 1 Short Beep Motherboard 1 Long Beep and 2 Short Beeps Video Card 1 Long Beep and 3 Short Beeps Memory

AMI BIOS BEEP CODES

/ The following are AMI BIOS Beep Codes that can occur. However because of the wide variety of different computer manufacturers with this BIOS the beep codes may vary.

Beep Code Descriptions 1 short DRAM refresh failure 2 short Parity circuit failure 3 short Base 64K RAM failure 4 short System timer failure 5 short Process failure 6 short Keyboard controller Gate A20 error 7 short Virtual mode exception error 8 short Display memory ReadIWrite test failure 9 short ROM BIOS checksum failure 10 short CMOS shutdown ReadIWrite error 11 short Cache Memory error 1 long, 3 short Conventional/Extended memory failure 1 long, 8 short Display/Retrace test failed

/'AWARD BIOS BEEP CODES

The following are Award BIOS Beep Codes that can occur. However because of the wide variety of different computer manufacturers with this BIOS the beep codes may vary.

Beep Code Description 1 long, 2 short Indicates a video error has occurred and the BIOS cannot initialize the video screen to display any additional information Any other beep(s) RAM problem.

If any other correctable hardware issues the BIOS will display a message.

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IBM BIOS

The following are IBM BIOS Beep Codes that can occur. Howeverbecause of the wide variety of models shipping with this BIOS the beep codes may vary.

Beep Code Description No Beeps No Power, Loose Card, or Short. 1 Short Beep Normal P0ST, computer is ok. 2 Short Beep POST error, review screen for error code. Continuous Beep No Power, Loose Card, or Short. Repeating Short Beep No Power, Loose Card, or Short. One Long and one Short Beep Motherboard issue. One Long and Two short Beeps Video (Mono/CGA Display Circuitry) issue. One Long and Three Short Beeps. Video (EGA) Display Circuitry. Three Long Beeps Keyboard / Keyboard card error. One Beep, Blank or Incorrect Display Video Display Circuitry.

MACINTOSH STARTUP TONES

TONES ERROR Error Tone. (two sets of different tones) Problem with logic board or SCSI bus. Startup tone, drive spins, no video Problem with video controller. . Powers on, no tone. Logic board problem. High Tone, four higher tones. Problem with SIMM.

PHOENIX BIOS BEEP CODES .(/

The following is for PHOENIX BIOS 03.07 OR 4.X

Beep Code Description / What to Check 1-1-1-3 Verify Real Mode. 1-1-2-1 Get CPU type. 1-1-2-3 Initialize system hardware. 1-1-3-1 Initialize chipset registers with initial POST values. 1-1-3-2 Set in POST flag. 1-1-3-3 Initialize CPU registers. 1-1-4-1 Initialize cache to initial POST values. 1-1-4-3 Initialize I/O. 1-2-1-1 Initialize Power Management. 1-2-1-2 Load alternate registers with initial POST values. 1-2-1-3 Jump to UserPatchO. 1-2-2-1 Initialize keyboard controller. 1-2-2.-3 BIOS ROM checksum. 1-2-3-1 8254 timer initialization. 1-2-3-38237 DMA controller initialization. 1-2-4-1 Reset Programmable Interrupt Controller. 1-3-1-1 Test DRAM refresh. 1-3-1-3 Test 8742 Keyboard Controller. 1-3-2-1 Set ES segment to register to 4 GB. 1-3-3-1 28 Autosize DRAM. 1-3-3-3 Clear 512K base RAM. 1-3-4-1 Test 512 base address lines. 1-3-4-3 Test 512K base memory. 1-4-1-3 Test CPU bus-clock frequency.

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1-4-2-4 Reinitialize the chipset. 1-4-3-1 Shadow system BIOS ROM. 1-4-3-2 Reinitialize the cache. 1-4-3-3 Autosize cache. 1-4-4-1 Configure advanced chipset registers. 1-4-4-2 Load alternate registers with CMOS values. 2-1-1-1 Set Initial CPU speed. 2-1-1-3 Initialize interrupt vectors. 2-1-2-1 Initialize BIOS interrupts. 2-1-2-3 Check ROM copyright notice. 2-1-2-4 Initialize manager for PCI Options ROMs. 2-1-3-1 Check video configuration against CMOS. 2-1-3-2 Initialize PCI bus and devices. 2-1-3-3 Initialize all video adapters in system. 2-1-4-1 Shadow video BIOS ROM. 2-1-4-3 Display copyright notice. 2-2-1-1 Display CPU type and speed. 2-2-1-3 Test keyboard. 2-2-2-1 Set key click if enabled. 2-2-2-3 56 Enable keyboard. 2-2-3-1 Test for unexpected interrupts. 2-2-3-3 Display prompt "Press F2 to enter SETUP". 2-2-4-1 Test RAM between 512 and 640k. 2-3-1-1 Test expanded memory. 2-3-1-3 Test extended memory address lines. 2-3-2-1 Jump to UserPatch1. 2-3-2-3 Configure advanced cache registers. 2-3-3-1 Enable external and CPU caches. 2-3-3-3 Display external cache size. 2-3-4-1 Display shadow message. 2-3-4-3 Display non-disposable segments. 2-4-1-1 Display error messages. 2-4-1-3 Check for configuration errors. 2-4-2-1 Test real-time clock. 2-4-2-3 Check for keyboard errors 2-4-4-1 Set up hardware interrupts vectors. 2-4-4-3 Test coprocessor if present. 3-1-1-1 Disable onboard 1/0 ports. 3-1-1-3 Detect and install external RS232 ports. 3-1-2-1 Detect and install external parallel ports. 3-1-2-3 Re-initialize onboard 1/0 ports. 3-1-3-1 Initialize BIOS Data Area. 3-1-3-3 Initialize Extended BIOS Data Area. 3-1-4-1 Initialize floppy controller. 3-2-1-1 Initialize hard-disk controller. 3-2-1-2 Initialize local-bus hard-disk controller. 3-2-1-3 Jump to UserPatch2. 3-2-2-1 Disable A20 address line. 3-2-2-3 Clear huge ES segment register. 3-2-3-1 Search for option ROMs. 3-2-3-3 Shadow option ROMs. 3-2-4-1 Set up Power Management. 3-2-4-3 Enable hardware interrupts. 3-3-1-1 Set time of day. 3-3-1-3 Check key lock. 3-3-3-1 Erase F2 prompt.

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3~3-3-3 Scan for F2 key stroke. 3-3-4-1 Enter SETUP. 3-3-4-3 Clear in-POST flag. 3-4-1-1 Check for errors 3-4-1-3 POST done--prepare to boot operating system. 3-4-2-1 One beep. 3-4-2-3 Check password (optional). 3-4-3-1 Clear global descriptor table. 3-4-4-1 Clear parity checkers. 3-4-4-3 Clear screen (optional) .

. 3-4-4-4 Check virus and backup reminders. 4-1-1-1 Try to boot with INT 19. 4-2-1-1 Interrupt handler error. 4-2-1-3 Unknown interrupt error. 4-2-2-1 Pending interrupt error. 4-2-2-3 Initialize option ROM error. 4-2-3-1 Shutdown error. 4-2-3-3 Extended Block Move. 4-2-4-1 Shutdown 10 error. 4-3-1-3 Initialize the chipset. 4-3-1-4 Initialize refresh counter. 4-3-2-1 Check for Forced Flash. 4-3-2-2 Check HW status of ROM. 4-3-2-3 BIOS ROM is OK. 4-3-2-4 Do a complete RAM test. 4-3-3-1 Do OEM initialization. 4-3-3-2 Initialize interrupt controller. 4-3-3-3 Read in bootstrap code. 4-3-3-4 Initialize all vectors. 4-3-4-1 Boot the Flash program. 4-3-4-2 Initialize the boot device. 4-3-4-3 Boot code was read OK

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BIOS/CMOS

BIOS-The BIOS (Basic Input-Output System) is a chip located on the motherboard, which handles all the startup routines necessary to get the computer running.

!n most PCs the BIOS will have 4 main functions:

POST - Test computer hardware insuring hardware is properly functioning before starting processor loading Operating System. Additional information on the POST can be found our POST I Beep Codes page. '

Bootstrap Loader - Process of locating the operating system. If capable Operating system loce.ed 8iOS will pass the control to it

BiOS- Software I Drivers which interfaces between the operating system and your hardware when running DOS or Windows you are using complete BIOS sepport .

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CMOS Setup - Configuration program. Which allows you to configure hardware settings including system settings such as computer passwords, time, and date? . Computer hardware are divided into 3 parts

BIOS manufacturers: American Megatrends, Phoenix, and Award

CMOS - Stores around 64K of Programming Short for complementary metal oxide semiconduc'or. Pronounced see-moss, CMOS is a widely used type of semiconductor. CMOS semiconductors use both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit typas is on at any given time, CMOS chips require less power than chips using just one type of transistor. This makes them particularly attractive for use in battery-powered devices, such as portable computers. Personal computers also contain a small amount of battery-powered CMOS memory to hold the date, tin e, and system setup parameters. .

How to enter a typical CMOS setup: When PC boots up you will be told to press a key to get to setup:

Award (DEL) Phoenix (F2) American Megatrends (CTRL+ESC) Others (F1, F10, ESC)

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Note: somenewmotherboard designs allowaccessto the CMOSsetupto be disabledthrough a motherboardjumper. If you cannotaccess the setupusingthe properkey commandsstatedabovecheckyourmotherboard settingsto see if the accesshas been disabled.

VIDEO CARD

Video Cards Manufacturers: ATI, STB, Diamond, Intel, GeoForce

Video cards (video boards I video display boards I graphics cards I graphics adapter) is a physical hardware circuit board(s) which connects to the Motherboard. When the video card is connected to a monitor it serves as the visual link between you and your computer, allowing you to view and manage your computers software data.

Typical Video Card Connectors

VG~(Video Graphics Adapter) use to connect analog monitors

DVI (Digital Video Interface) use to connect digital monitors

DMI (High Definition Multimedia Interface)

Video Cards are usually

Built-in to the motherboard (Integrated Video Card)

PCI-e (The fastest and the most expensive)

AGP (Extremely Fast)

PCI (Fast)

ISA (Cheap and Slow)

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Expansion Bus Chart: ..

IType of Bus

liSA

liSA

IPCI (Client)

II Bits Wide

II 118 bit

1116 bit . 1132 bit

[PCI (Se~er) 1164 bit

!AGP1X 1132 bit

]AGP2X 00132 bit

ITransfer Speed

I

!2.38MB/S

18MB/S

I 133MB/s

I266MB/s

I266MB/s

IFMB/S

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I

I I I I

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IAGP 4x 1132 bit 111,066MB/s I

IAGP 8x Il32 bit 112,133MB/s I AGP 8x 164 bit 114.266MB/S ](high-end)

I PCI-e I

june Widths II Peak unidirectional bandwidth I[peak full duplex bandwidth

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J Ix1 11250MB/s 11500MB/S I I x2 11500MB/s J11GB/S ---1- ".-------,"-_.- ---_.- -_ ...- - -- - ­

----------------------,

IX4 fl1GB/S 112GB/S 1------: Ix8 112GB/S 114GB/S I Ix16 114GB/S 118GB/S I I x32 (new) 1[8GB/S II 16GB/s I

Video Memory

32MB is a typical Video Memory if you are into gaming you will need more or you're-qoirrqtoturrthe-rrew Vista OS you are going to need at least 128MB If your a gamer 512MB or more is needed to play those complex games

High End Video Card sometimes contain their own BIOS, memory, cooling mechanism, processor, S Video connector and a TV Tuner connector for connecting your video card to your television. SLI nVidia Scalable Link Interface use for combining video cards ATI calls their Crossfire