GDDR3 is a dedicated graphics for high-performance graphics cardsStorage。GDDR3 is a standard that replaces GDDR. GDDR3 draws on many features of general DDR2, and further optimizes it to achieve higher data rate and lower power consumption.
Compared with DDR3, the architecture of GDDR3 is closer toDDR2, which is also developed by DDR2 and is dedicated to graphics cardsVideo memory。In terms of speed, GDDR3 is closer to DDR2, and has a certain gap with the newer DDR3.And GDDR3 and DDR3 are two completely different generations of products.Compared with GDDR, the main innovations of GDDR3 are as follows: the working voltage drops from 2.5V to 1.8V;On chip signal termination replaces the signal line in GDDR;Output driver of dynamic control impedance;4-bit prefetch and one-way single ended data strobe.The combined effect of all these features is higher data rate, better signal integrity and lower power consumption.Due to these changes, GDDR3storageYou can get a much higher data rate than GDDR and DDR2 standards.
On chip signal termination: with the increase of transmission frequency, the signal line must be terminated with resistance to prevent the reflected signal from interfering with the normal signal and affecting the signal quality.GDDR termination is realized by external resistance, which is welded on the PCB near the memory.External termination can slightly expand the frequency range of GDDR, but this type of termination scheme cannot meet the signal integrity required for upgrading GDDR3 to a frequency range of up to 800MHz or even higher.Therefore, GDDR3 uses on-chip signal termination, and its termination resistor is integrated in the memory chip.
Another important feature of supporting reliable and high-speed point-to-point transmission is the Vddq termination with adaptive impedance.GDDR3I/O interfaceIt is a pseudo open drain logic circuit with both ends of the bus terminated: 40 at one endOhmsThe other end of the impedance dynamic control driver is a receiver with 60 ohm signal line termination.
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Basic functions and task allocation in 3D graphics rendering system
The calculation of graphics in interactive 3D games can be divided intoSequential executionBasic steps of.In the first step, the 3D scene is calculated and generated according to the instruction result given by the player.The 3D scene represents the arrangement and position information of all objects in the virtual 3D world.This part of the calculation is completed by the CPU in the PC.Then the CPU transfers the 3D scene to the GPU.The task of GPU is to convert 3D scenes into 2D images that can be displayed on the display.This task performed by the GPU is called 3D rendering.
Many effects must be considered when producing actual images, such as color, texture, multiple extended light sources, shadow, reflection, transparency, light absorption, opaque materials, etc.To achieve all these effects, it requires strong computing power and particularly fast and widestorageInterface, so that random access to memory can be completed in the shortest waiting time.Memory bandwidthThe main driving factors of and capacity are the number of parameters that must be stored and quickly available, and the storage of intermediate results of highly repeated calculations.Don't forget that all these calculations must be completed in real time, and the computing power must exceed 40 frames per second.
Integrated and standalone graphics devices
In general,graphics systemIt can be divided into two categories: integrated graphics system and independent graphics system.In the integrated graphics system, the graphics processing unit is embedded in the PC chipset located on the notebook and desktop motherboard.For texture storage and caching, these integrated systems use the main memory of the PC.This practice limits the rendering performance of 3D graphics from two aspects.First, the maximum memory bandwidth is limited by the standard primaryMemory bandwidthSecondly, the graphics system must access the memory with the CPU and other clients on the PCProgram sharingThis bandwidth.Executed from "Tom's Hardware Guide"BenchmarkingIt can be clearly seen that the integrated system cannot provide sufficient rendering capability for advanced 3D games.
The independent graphics system consists of physically separate and independently working graphics processing units and dedicated graphics directly connected to independent GPUsstorageform.The independent graphics system is connected to the PC chipset via the standard PCI-E (formerly AGP) bus.The 3D processing performance of these independent GPUs has far exceeded the integrationGraphics ProcessorPerformance ofMemory bandwidthThe same is true of the requirements of.Benchmarking shows that independentgraphics system3 to 20 times more performance than integrated systems.Memory I/O technology and memory bandwidth play a key role in achieving this performance leap.
Fever and high-endGraphics cardUse special x32 structured graphics memory.Today these systems use GDDR3 memory with a clock frequency of 500~800MHz to form a 512MBFrame cache。These configurations provide GPU with memory bandwidth up to 410Gbps, equivalent to the most advanced PC hostMemory bandwidth12 times.The latest high-end notebook computer graphics system uses 500MHz GDDR3 memory to form 256MB frame cache, and the memory bandwidth provided to GPU can still reach five times of the main memory bandwidth of these laptops.
main streamgraphics systemUsually x16 structurestorageComponent.Most new mainstream graphics systems adoptclock frequencyAbout 400MHz DDR2 I/O technology.The performance of these systems is still significantly higher than that of integrated graphics systems.
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In the future, the increasingMemory bandwidthThe request of will continue.New technologies to improve image quality promote the increase of bandwidth.The upcoming high-definition display will further improve the resolution and the number of pixels rendered and displayed per frame.New rendering technologies, such as High Dynamic Range Rendering (HDRR), which can render the halo effect of each dense light source, are constantly increasing the complexity of performing operations on each pixel.
Except PCgraphics systemIn addition, graphics DRAM has other existing and upcoming markets.All major game consoles of the new generation will use GDDR3 graphicsstorage。The media center and media gateway used in the living room will also contain strong graphics performance, so graphics memory is also required.New 3D operating systems like Windows Vista will extend the demand for 3D rendering performance to almost every new PC.
