| |
| |
|
Hardware Information |
|
|
|
Expansion Cards Part 2: AGP
Expansion Cards Part 2: AGP The first in this series of Tech Tips on expansion cards took a look at the PCI slot, and the variety of devices that may find their home in one. Graphics cards are one of the many items that may be used in a PCI slot, but the demands of fast-paced video games require more speed and greater bandwidth than the PCI Bus can provide. Thus, the AGP slot was born, providing a dedicated interface to transfer graphics data only. The letters 'AGP' stand for Accelerated Graphics Port, and it is the term used to describe a dedicated, point-to-point interface that connects a video card directly to the system's memory and processor. AGP was first introduced by Intel in 1996, and is based off of their previous work in developing the PCI bus. Despite being based on PCI technology, the AGP and PCI slots on a motherboard are not interchangeable, so an AGP card can not be installed into a PCI slot, and vice versa. The initial release of AGP saw a sizeable performance boost over PCI, and the few revisions to the standard helped increase this even more as years went by. Other than having a dedicated path to the system's memory and processor, several other design features help AGP outperform PCI when it comes to graphics performance. Three of the other advancements: pipelining, side band addressing and graphics address remapping table are described below. Data transfer is improved through 'pipelining', a term used to describe the ability of an AGP graphics card to receive, and act upon, multiple instructions simultaneously. PCI data transfers require each piece of necessary information to be received separately before acting on any of it. Something called 'side band addressing' also provides AGP with a performance boost. Basically, additional lines of data are included with each packet to instruct the system as to where this data is to be used. PCI data transfers do not have this addressing information, and the system must look at the data itself in order to determine its destination. This is an obvious time saver, as well as a resource saver since the processor doesn't have to analyze all data just to determine the address. AGP allows the operating system to store texture maps in the system's memory which allows for more space, and perhaps faster access, rather than being limited to the use of graphics card memory only. Graphics art address remapping table, also known as GART, is a term used to describe a process that maps physical memory as virtual memory for the storage of texture maps. Basically, GART takes the system memory it is allowed to use to store texture maps and re-addresses it so that the system thinks these maps are now actually being stored in the frame buffer, or virtual memory. This might not sound like anything special, but this re-addressing requires that the texture map be written to memory only once and it is locked into place right where the AGP card can find it quickly. AGP can be broken down into different groups based on revisions to the specification (AGP 1.0, AGP 2.0, and AGP 3.0), as well as by the general speeds (1x, 2x, 4x, and 8x). There is overlap between the various categories, with AGP 1.0 supporting 1x and 2x, AGP 2.0 supporting 1x,, 2x, and 4x, and AGP 3.0 supporting 4x and 8x. For a complete break down of all the combinations available, please visit this page. Before taking a look at the specifications of AGP, let's have a refresher as to what was available on PCI prior to the birth of AGP. The standard PCI bus has a width of 32-bit, operates at 33 MHz, provides a maximum bandwidth of 132 MB/s (which has to be shared by all devices connected), and operates on 3.3V (or 5V on the original standard). The first version released was AGP 1.0 with a speed of 1x, which offered the following specifications: 32-bit bus width, operating at 66 MHz, providing a maximum bandwidth of 266 MB/s, and utilizing 3.3V. So, it can be seen that right out of the gate, AGP offered double the bandwidth of PCI. Each speed increase over 1x provided double the bandwidth as well as double the clock speed through the use of special signaling. So, AGP 2x offers a maximum bandwidth of 533 MB/s at a speed of 133 MHz, AGP 4x offers a maximum bandwidth of 1066 MB/s at a speed of 266 MHz, and AGP 8x offers 2.1 GB/s at a speed of 533 MHz. Given the timeline of the evolution of these cards, AGP 8x cards dominate today's marketplace. Finding some cards that are backwards compatible is possible, but the tricky part may be ensuring that the slot on the motherboard will accept them. Comparing the connector on this 128MB Apollo GeForce FX6600 GT card, to the connector on this 64MB Hercules 3D Prophet Ultra II card, and to the connector on this 256MB Chaintech GeForce FX5200 card shows that the first one is obviously different than the second two. The Apollo card is 8x only, the Hercules card is 4x/2x compatible, and the Chaintech card is 8x/4x, which results in different notches in the connector. AGP 1.0 only features a 3.3V connection, the release of AGP 2.0 saw the availability of both a 3.3V and 1.5V connector, and AGP 3.0 uses the same 1.5V, but only requires 0.8V for signaling. In order to protect cards of different voltages/formats, special keyed connectors were designed so that only the correct card could be installed on any motherboard. A universal connector was eventually released for AGP 1.0/2.0 which allowed cards of either voltage to be installed. For a schematic of the various connectors, please visit this page. Although AGP 3.0 can share in the use of a universal connection, many motherboards now only support 4x/8x cards based on the AGP 3.0 standard. Another specification for AGP was released between 2.0 and 3.0, and was referred to as AGP Pro. AGP Pro was intended to be the new standard to meet the demands of high powered graphics workstations, but it never really garnered widespread acceptance. Speeds of 1x, 2x, and 4x were supported with AGP Pro, and it utilized either a 3.3V, 5V, or a universal connector, similar to AGP 2.0. But, the AGP Pro connector was not the same size as the 'standard' AGP connector (see schematic at link above), meaning there were now three more possible connections to consider. An AGP Pro connection is longer than a standard AGP connection, and depending on the connector type, it could accept AGP 1.0 and 2.0 cards. Modern motherboards supporting AGP will specify what type of card is compatible with the board, so the guess work is eliminated when trying to match one with the other. For example, this Socket 754 Chaintech motherboard specifies that it has one AGP 4x/8x slot and this Biostar LGA 775 motherboard specifies that it has one 8x AGP slot. Final Words The AGP slot provided a much-needed boost to graphics cards as compared to the PCI slot, but game developers still managed to push the capabilities of this more powerful format to the edge. Something even faster was needed, and the next Tech Tip will take a look at that something in "PCI Express." PCI Express is not only destined to be the successor to AGP 8x, but due to its flexibility, perhaps to PCI as well. Computer tech tips and computer help
MORE RESOURCES:
Hardware - Google News |
|
|
|
RELATED ARTICLES
What is EEPROM ? EEPROM stands for Electrical Erasable Programmable Read Only Memory and also referred to as EPROM. As the name suggest, an EEPROM can be both erased and programmed with electrical pulses. What is ESR Meter? All capacitors have a certain amount of resistance to the passage of AC current. ESR (Equivalent Series Resistance) is the sum of all internal resistances of a capacitor measured in Ohms. Testing Diode -The Accurate Way on How to Test Semiconductor Diode Using Multimeter Testing diodes is different from testing a resistor because you need a skill to do it. If you do not know or wrongly test a diode you will be unable to repair the equipment. Ten Ways (plus 1) to Save on Printer Ink and Toner Cartridges Are you getting tired of the high cost of printing? You're not alone. Many consumers are up in arms. ESR Meter - The Capabilities To Check Beyond Electrolytic Capacitor There is something good about esr meter because besides electrolytic capacitor it can be use to measure other type of capacitors such as the non polarity capacitor. From esr meter specification, it is usually mentioned only checking the electrolytic type. Generation Laptop In May 2005 U.S hardware history was made. Best DVDs for Your Personal DVD Player When bought personal DVD player, the very next thing to do is purchasing an important DVDs collection with your favourite movies, documentaries, shows, cartoons. Here are few hints before buying. Rear Projection TV Facts - Understanding the Pros & Cons of Rear Projection in the Home Theater Rear Projection Television - An Affordable OptionA great deal of consumer appeal for Rear Projection TV systems arise out of the shear simplicity that this product offers as an immediate solution to getting a bigger TV.No mess, no fuss, if you have the space, either visit your local big screen retailer - or better still, check at your favorite online electronics superstore - to order your product and get it delivered in just a few days; unpack the product and there you have a big screen TV in your living room ready for immediate use!Rear Projection TV Facts:As already stated, rear projection offers a most immediate solution to getting a bigger TV. Wireless Networking, Part 1: Capabilities and Hardware Wireless Networking, Part 1: Capabilities and HardwareThese days it isn't uncommon for a home to have multiple personal computers, and as such, it just makes sense for them to be able to share files, as well as to share one Internet connection. Wired networking is an option, but it is one that may require the installation and management of a great deal of wiring in order to get even a modestly sized home set up. How To Buy The Perfect Student Laptop If you are like most student's, money isn't exactly growing on trees. Choosing the right laptop can be a matter of saving yourself a lot of heartache and money at the same time. Dusting Your Computer - Keeping it Cool My mother always told me to dust, but I never did, mostly because I was lazy, but also because I couldn't find any tangible benefit to dusting. I just didn't see how I'd benefit from my room or my things being less dusty. Testing Capacitor-How To Test A Capacitor When Breakdown Under Load Have you ever come across power problem where once you switch on the power supply and the fuse blow? You have checked all the components in the power (primary) and secondary section and all the components seems to be ok! Where is the fault? A fuse blown are usually caused by a shorted bridge rectifier, defective posistor, power transistor or FET, shorted primary winding of switch mode power tranformer, shorted secondary diode and etc. But in this article i'm gone to show you another secret of electronic troubleshooting tips. Got The Message that You Need New Ink Cartridges? We all know what it is like when that message flashes on the computer screen as you are printing off an important document. Your ink cartridge is low, replace soon! But, do you know what type of ink cartridges your printer needs? Do you know where to find ink cartridges to replace those? Is this going to be a long, difficult search that will cost you dearly? You don't have to dread that message at all. DVD Recorders: Getting Started IMO, these sd work 'like a VCR' as far as recording and playback. There are models w/ harddrives, VHS players, etc. How To Purchase A Quality Laptop Computers Case So you finally have that new laptop you have been drooling over for the past 3 months, only there is one problem -- You don't have a case for it. You've probably already laid down over a grand for the notebook and you're telling yourself that you don't want to spend another $70 for a case. Digital Camera Prints - Getting the Most for Your Money Digital cameras have really taken off in popularity in recent years. It's not uncommon anymore to see several people at an event with a digital camera. Printer Cartridges - Step Back in History You are working and trying to print out important documents when you discover that you are out of ink. This would have been a big drawback in the past. Intel Celeron vs Pentium The Celeron and Pentium Processors are two of Intel's best selling CPUs. They are found in a majority of home computer systems. Ergonomic Products 101 Human beings are scaling new heights day by day. Markets are becoming more and more complex and competitive. Lock Workstation Fast When you work in an office, it's important to lock your workstation every time you step away from your computer. A pain, but a security measure.
|
| home | index |site map |
| © 2006 |
