Introduction of related knowledge of graphics card

Many people still don't know much about graphics cards. Let me introduce some knowledge about graphics cards to you, and welcome your reference and study.

According to statistics, more than 80% of people's contact information is visual information, moving scenes and beautiful pictures, which outline interesting life and paint a colorful world.

Perhaps you haven't noticed, the small computer screen can show sunny spring, hot summer with trees, crisp and fruitful autumn, and winter covered with snow and ice. Higher-tech computer production has brought us to the magical and wonderful three-dimensional world.

In the computer, the display is the key graphical interface between the computer and the user. Colorful pictures can be as wonderful as they are, or as touching as they are. However, this requires the graphics card to send display signals to the display to control the display to display gorgeous colors, so both the graphics card and the display are indispensable parts of the computer display.

Graphics cards are becoming more and more important in multimedia technology and graphics processing technology. A good graphics card can be more expensive than the motherboard, which shows its proportion. At present? One board and one card? The popular collocation method also shows that computer designers attach importance to graphics cards. Display technology is constantly updated.

Terms related to graphic display technology

Knowing more about some graphic terminology can help us choose a more suitable graphics card. Here are some terms that are often used when talking about display technology.

Prediction in graphics accelerator card

◇ color depth: used to describe how many colors a graphics card can display at a time. 8-bit color depth can display 256 colors; 16 bit color depth can display 65536 colors; 24-bit color depth can display 16M color.

◇ Dual-port memory: It is a kind of RAM with two ports. Graphic data can be directly input from one port and output from another port, thus further improving the speed. Both VRAM and WRAM are dual-port memories.

◇EDO VRAM: It is a faster VRAM.

◇RAMDAC: Digital-to-analog converter, which is used to convert digital information processed by PC functions into analog signals that can be displayed by the display. The faster the change, the higher the screen refresh rate you can get.

◇ refresh rate: the number of times to redraw the screen per second. If the screen refresh frequency is lower than 55Hz, it will flicker, which is easy to make people's eyes tired.

◇SGRAM: a kind of synchronous memory, which can theoretically double the processing speed of graphics cards. SDRAM and SGRAM, they are basically the same, but SGRAM has some graphics enhancement features.

Video interpolation: When you want to enlarge a viewport, unless your graphics card uses interpolation processing, the edges of the image will become uneven. It is generally desirable to be able to interpolate in both x and y directions.

3D software terminology

◇API: (Application Programming Interface) API is a software interface for communication between 3D programs and 3D graphics accelerator cards. In order to make 3D graphics card can be used to accelerate the execution of 3D games, game development should use the API that graphics card can support.

◇Direct3D: Microsoft's Direct3D originally hoped to become a standard supported by all 3D software and 3D graphics cards. However, due to the unsatisfactory performance of Direct3D, game developers often use API for specific 3D graphics cards.

◇OpenGL: It is a professional API, which is widely used in high-end CAD software. Software developers are considering using OpenGL instead of Direct3D as the API for software development.

Terminology of 3D image technology

Alpha blending: It is a color blending method, which can blend two overlapping texture images to make one of them look transparent. For example, the laser beam flame is reflected on the green wall. The image of the laser beam is surrounded by a black frame. In order to make the laser beam look more realistic, it is necessary to remove the black, and the green of the wall should be mixed with the color of the beam.

◇ Filtering: Eliminate the color block feeling in 3D images and make the images look smoother.

◇ Fogging: When a 3D object moves, it mixes with a fixed color, making it look as if it gradually disappears or appears from fog or darkness.

◇MIP mapping: Save a texture map as several different sizes to adapt to objects of different sizes. This helps to display moving texture map objects. Without MIP mapping, when 3D chip compresses or expands texture graphics to adapt to the change of object size, it will feel flicker at the edge of texture mapped objects. Using MIP mapping, there is not much compression processing. The graphics acceleration chip will quickly choose to use larger or smaller texture graphics according to the size of the object.

Perspective correction: Texture-mapped 3D objects look more realistic at different angles and distances.

Texture mapping: pasting a bitmap on the surface of a 3D object can make the object look more realistic. For example, Microsoft's monster truck crazy games, when you move in the scene, the graphics card will constantly paste the sand position map on the sand dune to make the sand dune look more realistic.

AGP (Accelerated Graphics Port) graphics acceleration interface standard.

AGP is a new generation of graphics interface technology, which can greatly improve the display ability of three-dimensional graphics. At present, major graphics card manufacturers have launched a large number of AGP graphics card products, and the motherboard with AGP interface has also been put on the market. AGP 3D graphics cards are flooding into the graphics card market.

Although the graphics processing ability of PC is getting stronger and stronger now, the performance of PC platform is still limited to completing detailed large-scale 3D graphics description. In order to make PC's 3D application capability comparable to that of graphics workstation, Intel developed AGP. The main purpose of launching AGP is to greatly improve the display ability of mainstream PC graphics, especially 3D graphics. Combining DIB (Dual Independent Bus) technology and MMX technology of Pentium II, AGP will become the standard of the new generation of commercial computers.

What is AGP?

1 PCI bus in 3D application

AGP mainly aims at the data transmission bottleneck of PCI display card when dealing with animation and 3D drawing. As the processor becomes faster and faster, the bottleneck will become more serious, especially in the case of 3D images.

In 3D graphics rendering, not only image data, but also Z-axis distance data, TextureData and Alpha transform data are stored in the display memory of PCI display card. The more display memory for storing texture data, the better. From the point of view of the whole system, it is not as cost-effective to increase the main memory as to increase the video memory, and it is more effective to store the texture data in the main memory than in the video memory. In other words, when the application ends, the main memory space occupied by it can be recovered, and the texture data will not occupy the main memory space forever.

Unfortunately, when the texture data is moved from the main memory, the bottleneck of data transmission is also transferred from the memory bus on the graphics card to the PCI bus, and the transmission volume of texture data will exceed 100 MB/ sec. The existing PCI bus is far from meeting the requirements, so a new interface like AGP is needed to connect the main memory and the graphics card.

2.2 structure. Accelerated Graphics Port (which enables 3D graphics to be displayed at a faster speed on ordinary personal computers).

The purpose of AGP is to achieve high-performance 3D graphics rendering function at a relatively low price. To this end, Intel extended the three main specifications of PCI and defined AGP:

(1) pipeline processing of data reading and writing operations;

(2) The data transmission period is133mhz;

(3) The address signal is separated from the data signal.

The principle of AGP is to set the display chip independently on the system bus and connect the display chip directly with the memory controller circuit of the chipset. Here? Point to point? In the connection, the two edges (rising edge and falling edge) of the clock signal are also used for data transmission, so the speed is doubled. Because of point-to-point connection, a system can only have one AGP, so AGP will not replace PCI bus. The data transmission speed of the first generation AGP is 66MHz, which is twice that of PCI bus. The second generation AGP will reach 133MHz, which is enough to meet the requirements of playing DVD discs with software. The highest data transmission speed can reach 533 MB/ s, which is about four times that of current PCI. The comparison between PCI and AGP is shown in the following table:

Comparison between PCI and AGP

PCI bus AGP

Transmission mode synchronization

Memory priority access is not supported.

Data line bit width 32 bits 32 bits

Bus clock 33 MHz 66 MHz

The highest data transmission speed is 133 MB/ s 533 MB/ s.

The maximum number of expansion cards that can be connected is 5, 1.

Number of signal lines 49 65

The mapping processing of 3D graphics requires high data transmission speed between the display chip and the display memory. At present, most graphics cards use faster memory, but this will increase the cost of graphics cards. One of the compromise methods is to move the texture data from the main memory, which can reduce the capacity of the main memory and thus reduce the cost of the graphics card.

AGP is not only used for 3D graphics, but also effective for 2D graphics. Because the graphics card is connected to the main memory through AGP and chipset, the data transmission speed between the display chip and the main memory is improved, so that the texture data originally stored in the display memory can be directly stored in the main memory, which can improve the memory bus utilization efficiency of the main memory, improve the picture update speed and the transmission speed of data such as Zbuffer, and also reduce the load of PCI bus, which is beneficial to other PCI devices to give full play to their performance. You know, in the PC98 specification, ISA bus has been canceled, and ISA devices will eventually be eliminated. Therefore, it is a very necessary step to migrate the graphics card that occupies a lot of bandwidth of PCI bus to AGP.

AGP also has good performance in the transmission effect of image data. When MPEG-2 image data is decompressed by CPU, it needs to be written into the display memory through the bus. The decoded MPG2 image data of the whole picture needs to be transmitted at the speed of 15 ~ 20mB/ s. Although the actual data transmission speed of PCI bus is 27 ~ 33mb/ s, if the data transmission is not coordinated properly, the picture will be very unsmooth.

At present, there are still two factors that limit the development of AGP. One is the data transmission speed of main memory. The display chip supporting AGP needs to access the main memory when rendering 3D graphics, so it will increase the memory bus traffic of the main memory, which generally requires a speed of more than 800 MB/ s.. But at present, the data transmission speed of main memory is mostly 200 ~ 300 MB/ s. At this speed, even if AGP is used, it is impossible to make a detailed three-dimensional graphic description. In order to achieve the data transmission speed of 800 MB/ s, it is necessary to have high-speed DRAM, such as SDRAM, RDRAM or other devices above 100MHz, such as S-gram and VRAM. Another problem of AGP is the compatibility of graphics cards.

future

AGP is an open specification, and manufacturers do not have to pay patent fees. At present, 3D graphics card manufacturers such as 3Dfx, 3Dlabs, ATI, CirrusLogic, Rendition, S3, Trident, etc. Indicates support for AGP, and some prototype products have been launched. Intel not only signed a contract with Microsoft, but also encouraged many graphics card manufacturers to adopt AGP. At present, some high-performance PCs have been adopted first. Therefore, AGP can be popularized in a short time. Intel believes that by the year 2000, 90% of personal computers will be equipped with AGP display cards.

In order to give full play to the advantages of AGP, Microsoft has supported AGP function in its new versions of Windows 98 and Windows NT 5.0, and provided programming interfaces for software vendors through DirectDraw API.

Motherboards with AGP interface have been put on the market. For example, the latest motherboards of elite, Asus, Zhong Ling and other companies all adopt Intel 440LX and 440BX chipsets supporting Pentium II, while other chipset manufacturers such as VIA have also introduced chipsets supporting Socket 7 motherboard AGP of Pentium MMX CPU.

The graphics cards of AGP interface are all 3D graphics cards, using high-speed memory such as SDRAM or RDRAM. Trident's 3D images 985 and 875 both support AGP and have TVOut function.

From the perspective of prototype products, AGP will not significantly increase the cost of graphics cards, but it is much more powerful. For example, Trident's 3D Image 985, besides the chip itself, has an MPEG2-2 decompression chip which can play DVD discs, fully meeting the needs of future multimedia computers.

Talking about AGP technology

1.AGP to speed up graphics/video processing? Specific medicine?

As mentioned above, what is the high-speed bottleneck of 3D graphic display? Graphic texture processing? , need to be 100Mbps (resolution is 640? 480 points) ~ 150 Mbps (resolution is 800? 600 points) to transmit a large amount of bitmap data, but at present, the transmission rate of all PCI buses is too low to meet the requirements of transmission speed.

In PC, three-dimensional graphics processing can be roughly divided into? Geometric transformation? And then what? Paint and color? Handle. Both of these processes are undertaken by the overloaded CPU. To this end, use a three-dimensional graphics chip instead of CPU to handle a lot of processing? Paint and color? . In order to reduce the cost of graphics card, we must try to reduce the capacity of graphics memory, so we store texture data in main memory. However, in the current system, main memory and video memory are connected through PCI bus, and its maximum transmission rate is 133Mbps, while data is sent to main memory through HDD, LAN, sound card, etc. They are all through PCI bus, but the actual transmission rate is much lower than 133Mbps. Therefore, the special interface AGP for graphics data is introduced.

As we can see, AGP directly connects main memory and graphics memory. The width of AGP bus is 32 bits, the clock frequency is 66MHz, it can work at 133MHz, and the highest transmission rate can reach 533MBps. The primary purpose of AGP is to put texture data in main memory to reduce the capacity of graphics memory, so as to produce cheap and high-performance graphics cards. AGP is not only used for 3D image processing, but also for animation reproduction. The decompression of MPEG2-2 animation data requires a transmission rate of about 30Mbps, but PCI bus is not competent, and APG is more comfortable.

It is of great significance to adopt AGP in data transmission. The current PCI bus is the bottleneck of transmitting video and 3D graphics data. The transmission rate of AGP is 533Mbps, which is four times that of PCI. It is expected to become a new generation of buses to eliminate this bottleneck.

Where is Intel, the overlord of PC CPU chip? Graphic controller? 97? It is said that starting from 1997, the following three devices will be standard in PC: 3D graphics drawing device equivalent to arcade; Reproduce MPEG2-2 video equipment recorded in DVD-ROM with software; The video conference equipment that conforms to the technical standard of H.320/H.324 (ITU-T: Electrical Communication Standardization Department of International Electric Union) advocates the use of AGP and MMX to realize the above three kinds of equipment. Accordingly, X86 compatible chip manufacturers expressed support for MMX, and graphics control chip manufacturers also expressed the need to adapt to AGP.

MMX is an internal problem of the processor, while AGP will change the architecture of personal computers. In order to adapt to AGP, graphics control chip and memory /PCI control chipset must be redesigned.

In fact, AGP improves the performance of 3D graphics? A panacea? . However, it must try to reduce the cost while improving the performance, so that it can be configured in a general-price PC.

Unfortunately, AGP sacrifices universality and scalability. The reason is that only 3D graphics control chips can be connected to AGP. Although personal computers are equipped with multimedia boards, such as graphics, MPEG2-2 decompression and video capture attached to 3D devices, AGP? The beneficiary is only the graphics card. Therefore, I dare not assert AGP? Is it a good choice for a new generation of public transport? .

2.SGI？ Find a new way?

SGI Company proposed another alternative to AGP. In June 1996, 1 1, O2 graphic workstation with advanced UMA (unified memory architecture) was launched. O2 graphics workstation is the first system in the industry to adopt a unified memory structure. Based on its 64-bit MIPS RISC microprocessor, it integrates three-dimensional graphics and image processing, video, audio and compression functions, thus achieving superior performance at a lower price. It breaks through the traditional data transmission barrier based on bus, so that CPU graphics and image processing and I/O can directly access the memory at the speed of 2. 1Gbps, and transmit information quickly.

The focus of O2 graphic workstation is to reduce the cost and improve the performance as much as possible. Using UMA technology, four kinds of peripheral chips such as graphics controller and video processor and main processor can use main memory (SDRAM). Generally speaking, if UMA devices are used, when the access applications of multiple peripherals are concentrated in main memory, the performance will decrease. Therefore, in O2, an ultra-high-speed bus with a width of 256 bits and a clock frequency of 66MHz (the maximum transmission speed is 2. 1Gbps) is used to connect the main memory to suppress the performance degradation.

UMA plays an active role in all multimedia data operations, such as 3D graphics rendering, video reproduction and video capture. For example, the performance of 3D graphics depends largely on memory capacity and memory access performance, because Z buffer and texture data area are frequently accessed when processing graphics. According to Microsoft's calculation, at 640? In the popular color representation mode of 480 pixels, when a 3D object is drawn using a texture map with binary filtering and a 24-bit Z buffer, a memory bandwidth of about 30Mbps is required. In addition, only Z buffer and texture data are stored at this time, which requires 4MB of memory. If UMA equipment is used and the graphics control chip uses the main memory as the frame buffer, then the special frame buffer can not be used, and the texture data area can be guaranteed to the maximum extent in the empty main memory area, which is expected to further improve the performance of 3D graphics.

UMA is particularly effective in video capture. Using a camera to capture video, and then pasting it as texture data of a 3D object, the video image can be reproduced in real time. Because of the use of UMA mechanism, as long as its memory pointer is passed to the graphics control chip as a pointer to capture data, the captured data can be sent to the main memory.

3.AGP is not a bus

It is the same as UMA, except that AGP is only a technical standard that enables peripheral devices to access memory at high speed. Specifically, the 3D graphics chip is connected with the memory /PCI chip, and the 3D graphics chip can use the main memory as a frame buffer to realize high-speed access. Strictly speaking, AGP is not a bus, it only considers one-to-one (point-to-point) connections? Port? .

Therefore, the main goal of AGP is to draw three-dimensional graphics. The data bus width of AGP is 32 bits, and it has two working frequencies of 66MHz and 133MHz, with the highest data transmission rates of 266Mbps and 533Mbps respectively. The memory /PCI control chipset corresponding to AGP is equipped with a chip named? GART (graphic address remapping table) Table, a 4KB 3D graphics chip, can freely map main memory to its own address space. The mapping area in main memory can be discontinuous, but it must be in 4KB units.

In addition, AGP has a positive effect on the reproduction of MPEG2-2 video. However, this is limited to the case where the processor is used to decompress MPEG2 video data without special decompression hardware. When decompressed by the processor, the decompressed video data can be transmitted to the video memory through AGP when the picture is displayed. However, if a dedicated MPEG2-2 decompression card is used, the decompressed data must be transmitted through PCI bus instead of AGP. In the MPEG2 specification, 7200 is mainly used? 576 pixels, 30 frames/second video. Theoretically, the data transmission capacity of 36Mbps is needed to transmit decompressed data. The actual transmission rate of PCI is 30 ~ 40 Mbps. If you use PCI bus to transmit, the picture will shake. Intel recommends using the main processor to decompress MPEG2 video. In AGP, MPEG decompression card is no longer considered.

Video capture card can't be connected with AGP card, and it can't be used for texturing only by passing the memory pointer of data acquisition to a graphics control chip like O2.

4. How strong is 4.AGP? Patch? colour

Many PC graphics experts predict that it will take two or three years for O2 architecture to be applied to PC. ? For example, relevant institutions have formulated the technical standard of PCI bus, with a width of 64 bits and a clock frequency of 66MHz. Its theoretical data transmission speed is 533Mbps, which is the same as AGP. In addition, VESA (video electronics standards association) has also planned to establish UMA technical standards for all external devices connected to PCI bus. If the UMA mechanism is installed on the PCI bus with a width of 64 bits and a clock frequency of 66MHz, its structure will become an O2 graphic workstation, so that all multimedia mechanisms can work smoothly.

Peripheral devices such as SCSI control chip, modem and serial/parallel controller do not need to transmit data faster than the current PCI bus, but they must work at the clock frequency of 66MHz. In this way, the manufacture of various such control chips not only increases the cost, but also is complicated to debug. However, if new equipment is introduced to replace AGP in the next 1 ~ 2 years, new machines must also be purchased, which will inevitably hinder the popularization of PC.

5.AGP is a feasible solution at present.

In fact, AGP is the most realistic solution to realize PC graphics and video processing functions. O2 is the technical standard for high-performance and high-price workstations exclusively formulated by SGI. It is very different from a PC made up of products from many manufacturers. For example, it connects the main memory to the bus with the highest data transmission speed of 2. 1Gbps, and integrates the reproduction mechanism of drawing 3D graphics and the main memory controller into one chip. These are technologies that can only be realized by closed independent manufacturers. In a PC with many manufacturers' products, it is really necessary to realize a device completely corresponding to O2. Reluctant? . In addition, this is also related to the fact that the PC regards the open environment as? Soul? Spirit is different.

On the contrary, AGP can be developed under the design idea of configuring AGP in low-cost PC, and the corresponding device (graphics control chip) is simple to manufacture and low in cost. For example, because AGP is only limited to connecting one device (except the main memory /PCI control chipset), the connected devices are easy to develop, and there is no need to install a special AGP arbitration circuit in the main memory /PCI control chipset, which can reduce the cost. In fact, the so-called PCI bus is the bottleneck of transmitting a large amount of data, which only refers to 3D graphics chips.

AGP is essentially an extension of PCI technical standards. This is also to simplify the development and design and make it similar to PCI bus. AGP is different from PCI bus in that its address lines and data lines are separated (PCI has 49 signals, while AGP has 65). Achievable? Assembly line? Processing, in order to improve the actual data transmission rate; Address lines and data lines are separated, and there is no switching? Cost? This improves the performance of random access to the main memory.

What are the memory /PCI control chipsets? Deal with things? Queue, used to realize pipeline? Deal with it? . Once the graphics control chip sends a request to the main memory /PCI control chipset, it immediately releases the bus. The main memory /PCI control chipset can store multiple application commands in the queue and process and respond in turn according to the priority. The graphics control chip can accept the processing results within the data waiting time, so the overall use efficiency of the bus can be improved.

6. Thinking about the overall structure of PC.

Although AGP is a feasible scheme to realize the graphics and video processing function of PC, it still has strong? Patch? Technical standard of color. Can AGP be commensurate with investment? Permanent? Equipment? Settle down? Or a flash in the pan like the VL bus in the past? It's hard to be sure now. On the contrary, AGP was introduced to popularize the demand of 3D graphics. What if the demand for 3D graphics? Shrinkage? The failure of VMC(VESE Media Channel) and SFBI (Shared Frame Buppzer Interconnect) may be repeated.

How to use multimedia PC in the future is still inconclusive. Intel's prediction is only based on playing PC? Games? The number of users of MPEG2-2 video images will increase dramatically. More importantly, the PC should have the ability to play? Games? , play MPEG2 video, and even play video capture. From this perspective, there will be new applications and services, and a brand-new multimedia world will be presented to us.

In order to further popularize PC and open up a huge home PC market, we should not only pay attention to immediate interests, but also have a long-term multimedia bus. Today, it is extremely urgent to design an ideal overall structure of multimedia PC.