Video card memory

Storage used by computer display adapter

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synonym Video memory (Video memory) generally refers to video card memory

Video memory, also called Frame cache , which is used to store Graphics card chip Render data processed or to be extracted. like computer The video memory is used to store the data to be processed Graphic information Part of.

Chinese name: Video card memory
Foreign name: Video Memory

Alias: Video memory Frame cache
Category: computer hardware

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eight Clock cycle

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Video memory

Like computer memory, video memory is used to store data to be processed Graphic information Part of. The picture we see on the screen is composed of pixels Dot composition Each pixel uses 4 to 32 or even 64 bit data to control its brightness and color. These data must be saved in video memory and then submitted to Display chip And CPU, and finally convert the calculation result into Graphic output To the display. Video memory, like motherboard memory, performs the function of storage, but it stores the information of each pixel output from the video card to the display. Video memory is a very important part of video card, Display chip After processing the data, it will be saved to video memory, and then RAMDAC（ Digital to analog converter ）Read data from video memory and digital signal Convert to analog signal , finally by Screen display Come out. In advanced Graphics accelerator Video memory is not only used to store graphic data , and was also Display chip It is used for 3D function operation. Advanced in nVIDIA Display chip And has developed and CPU Parallel "GPUs"（ Graphics Processing Unit ）。 “ T&L ”(deformation and lighting), etc high-density The operation is completed by GPU on the video card, which makes the dependence on video memory more serious. Because of the role of video memory in the video card, it is obvious that the speed and bandwidth of video memory directly affect the overall speed of the video card. Video storage as memory It has also experienced multiple Development stage It can even be said that the development of video memory is more active than motherboard memory, and has more varieties and types. Widely used Video memory type yes SDRAM and SGRAM , better performance DDR memory First, it is applied to the graphics card, which improves the overall performance of the graphics card. DDR is guided by the success on the graphics card, Comprehensive development When it comes to motherboard systems, an era of DDR "three or two years ahead" will be presented to the world.

Mainly generated

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The graphics card is one on the motherboard BGA package Of chipset , similar to CPU （ Central Processing Unit ）, which is called GPU (Graphics Processing Unit) in the industry. There are nVIDIA and AMD Two manufacturers. Graphics chip It is equivalent to the CPU of the graphics card, but its main task is to process display information process information It will generate a large amount of temporary data (unprocessed, being processed, and completed) during the process of. This requires a special place to store these temporary data, that is, video memory. It may also be a chip or just a part of the chip, depending on the hardware design (independent video card and integrated graphics ）。 As for viewing the video memory size. It is generally displayed when you start up the computer. You can also click Properties Settings Advanced on the desktop-- Adapter --Check "Memory Size" (XP system); Or right click on the desktop-- Screen resolution --Advanced settings -- adapter. View the adapter information (Win7 system).

PCB : Yes printing Circuit board (Printed circuit board, PCB). It appears in almost every electronic device. If there are electronic parts in a certain device, they are all embedded on PCBs of different sizes. In addition to fixing various small parts, the main function of PCB is to provide mutual support between the upper parts Electrical connection 。 along with Electronic equipment More and more complicated, more and more parts are needed, and the lines and parts on the PCB are more and more dense. Bare plate (no parts on top) is also often called“ Printed circuit board Printed Wiring Board（PWB）”。 The base plate of the board itself is made of insulating and heat-insulating materials that are not easy to bend. The small line material visible on the surface is Copper foil The original copper foil is covered on the whole board, but part of it is etching After being disposed of, the remaining part will become a mesh of tiny lines. These lines are called conductor patterns or wiring, and are used to provide circuit connection of parts on PCB. Generally, the color of PCB is green or brown, which is the color of solder mask. It is insulated Protective layer It can protect copper wires and prevent parts from being welded to incorrect places. stay Solder mask A layer of screen will be printed on the Print side （silk screen）。 Usually, words and symbols (mostly white) will be printed on it to mark the position of each part on the board. The screen printing surface is also called the icon surface.

working principle

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The working principle of the graphics card is that before the graphics card starts to work (graphics rendering modeling), the required materials and textures are usually data transfer Into video memory. At the beginning of work (modeling and rendering), these data are generated by AGP bus Transmission, Display chip The data stored in the video memory will be extracted through the AGP bus. In addition to the modeling and rendering data, there are a lot of vertex data and work Instruction flow The data needs to be exchanged. These data are converted to analog signal The output to the display end is the image we see. Display chip With the increasing performance, its data processing ability is becoming stronger and stronger, which makes the video memory data transmission Quantity and Transmission rate It also has higher requirements, and the video card has higher requirements for video memory. Carrier Exchange volume The size and speed of Video card core The efficiency of video memory is very important, and how to effectively improve the efficiency of video memory is to improve the overall efficiency of video memory Display card The key to effectiveness.

Distinguishing types

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overview

As Display card As an important part of Display chip And gradually changed. From early EDORAM MDRAM 、SDRAM、SGRAM、 VRAM The DDR SDRAM video memory widely used by WRAM has experienced many generations of progress. Used in the market Video memory type There are mainly three kinds of SDRAM, DDR SDRAM and DDR SGRAM. SDRAM particles are mainly used in Low end video card In general, the frequency does not exceed 200MHz. It has no advantages over DDR in price and performance, so it is gradually replaced by DDR. DDR SDRAM is the mainstream in the market (including DDR2 and DDR3). On the one hand, the process is mature, and mass production leads to lower costs, making it cheap; On the other hand, it can provide high operating frequency and bring excellent data processing performance. As for DDR SGRAM, it is designed for graphics card manufacturers to meet the needs of plotters. In order to enhance the efficiency of graphics access processing and drawing control Dynamic random access memory (SDRAM). SGRAM allows you to modify or access data in memory individually in blocks a central processor (CPU) synchronization can reduce the number of memory reads and increase the efficiency of the drawing controller. Although it has good stability and good performance, its overclocking performance is poor and is rarely used at present.

FPM DRAM

FPM DRAM (Fast Page Mode RAM): fast page mode memory. It is a kind of memory (also used as video memory) that was widely used in the 486 period. 72 lines, 5V voltage, 32bit bandwidth, basic speed of more than 60ns. Its reading cycle starts from the triggering of a line in the DRAM array, and then moves to Memory address The indicated location contains the required data. The first piece of information must be verified to be valid and stored in the system before it can be ready for the next cycle. This introduces the "waiting state", because the CPU must wait foolishly for the memory to complete a cycle. One important reason why FPM is widely used is that it is a standard and safe product, and it is very cheap. But its performance defects led it to be EDO DRAM Instead, the video card of this kind of video memory no longer exists.

EDO

EDO (Extended Data Out) DRAM. Compared with FPM, EDO DRAM is 5% faster. This is because EDO has a logical circuit By this way, EDO can read the next data into memory before the end of the last memory data reading. Designed as system memory EDO DRAM is very expensive originally, just because the PC market needs an alternative FPM DRAM Therefore, it is widely used on the fifth generation PC. EDO video memory It can work at 75MHz or higher, but its standard working frequency is 66MHz, but its speed still cannot meet the needs of display chips, and it has become a video memory only available on "antique" products.

SGRAM

SG RAM SYNCHRONOUS GRAPHICS DRAM is an abbreviation for Synchronous Graphics RAM, which means that synchronous graphics RAM is a kind of video memory specially designed for video cards and has strong graphics read-write ability SDRAM Improved. It improves the low transmission rate of inefficient video memory in the past Display card The improvement of performance creates conditions. When SGRAM reads and writes data, it does not read one by one, but takes "Block" as the unit, thus reducing the times of overall memory reading and writing, and improving the efficiency of the graphics controller. But its design Manufacturing cost It is higher, and is more used in high-end graphics cards at that time. At present, this kind of video memory has been basically not used by manufacturers, but replaced by DDR video memory. SDRAM， Synchronous DRAM (synchronous dynamic random access memory) was once the most widely used type of PC Memory type Even today, SDRAM still has a place in the market. Since it is "synchronous dynamic random access memory", it means that its working speed is the same as that of the system Bus speed Synchronized. SDRAM memory It is divided into PC66, PC100, PC133 and other specifications, and the number after the specification represents the maximum normal operation of the memory system bus Speed, such as PC100, means that this memory can work synchronously in the computer with 100MHz system bus. And system bus Speed synchronization, that is, with the system Clock synchronization , which avoids unnecessary waiting cycles and reduces data storage Time. Synchronization also makes Storage controller Know which one Clock pulse The period is used by the data request, so the data can start to transmit during the pulse rise period. SDRAM uses 3.3V working voltage , 168Pin DIMM Interface with 64 bit bandwidth. SDRAM is not only used in memory, but also in video memory. SDRAM can work synchronously with CPU, without waiting cycle and reducing data Transmission delay 。 Advantages: Low price, it has been widely used in low-end video cards. SDRAM has lost its popularity since DDR SDRAM became mainstream. At present, SDRAM can only be used in the lowest end products or Flea market Only then can we see such video storage products.

DDR There are two kinds of video memory. One is DDR memory, which we are used to. Strictly speaking, DDR should be called DDR SDRAM. The other is DDR SGRAM, which is rarely used.

DDR SDRAM

DDR SDRAM People are used to calling DDR SDRAM DDR. DDR SDRAM is the abbreviation of Double Data Rate SDRAM, which means double rate synchronous dynamic random access memory. DDR SDRAM It is developed on the basis of SDRAM and still uses the SDRAM production system. Therefore, for memory manufacturers, it is only necessary to slightly improve the equipment that makes ordinary SDRAM to realize the production of DDR memory, which can effectively cost reduction 。 RAM transmits data only once in a clock cycle. It transmits data during the rising period of the clock; DDR memory transmits data twice in a clock cycle. It can transmit data once in the rising and falling periods of the clock, so it is called double rate synchronous dynamic random storage 。 DDR memory can be stored in the same Bus frequency Release higher data Transmission rate 。 Compared with SDRAM: DDR uses a more advanced synchronization circuit, so that the main steps of the designated address, data transmission and output are executed independently, while maintaining full synchronization with the CPU; DDR uses DLL (Delay Locked Loop, which provides a Data filtering Signal) technology, when the data is valid, the storage controller can use this data filtering signal to accurately locate the data, output it every 16 times, and resynchronize the data from different memory modules. DDL does not need to be improved in essence clock frequency Can double the speed of SDRAM, which allows Clock pulse Of Rising edge and Falling edge Read data, so its speed is twice that of standard SDRA. DDR SDRAM is the most widely used Video memory type More than 90% of video cards use this type of memory.

DDR SGRAM

DDR SGRAM It is developed from SGRAM. It also transmits data twice in a clock cycle. It can transmit data once in the rising period and once in the falling period of the clock. It can be changed without increasing the frequency Data transmission rate Double. DDR SGRAM is better than DDR SDRAM in performance, but its cost is still higher than DDR SDRAM, and it is only used in a few products. And its Overfrequency The capability is weak, and it is easy to be damaged due to overclocking due to its structural problems. DDR2 video memory It can be regarded as an upgrade and expansion of DDR video memory. DDR2 video memory takes the "2 bit" of DDR video memory Prefetch (2-bit prefetch) technology is upgraded to the "4-bit prefetch" mechanism Core frequency Lower its validity Frequency ratio DDR video memory has been doubled Bit width In the case of Video memory bandwidth It has also doubled, which is very beneficial to the performance improvement of the graphics card. Technically, the DRAM core of DDR2 video memory can be accessed in parallel. It processes 4 data in each access instead of 2 data in DDR video memory DDR2 The video memory can process 4bit data in each clock cycle, which is twice as much as the 2bit data processed by traditional DDR video memory. Compared with DDR video memory, another improvement of DDR2 video memory is that it uses 144Pin spherical Pin Of FBGA Packaging method Replace the traditional TSOP The working voltage is also reduced from 2.5V to 1.8V. As DDR2 video memory provides higher frequency, the performance is improved correspondingly, but it also brings Calorific value The disadvantages of. Combined with structural constraints, it is impossible to adopt cheap TSOP package The BGA packaging with higher cost has to be adopted (the initial capacity of DDR2 is insufficient, and the cost problem is even worse). High calorific value and high price have become common problems in using DDR2 video memory cards. For example, GeForce FX 5800/5800Ultra series video cards that first used DDR2 video memory are relatively failed products. For the above reasons, DDR2 is not widely used in mainstream video cards.

DDR3

DDR3 Video memory can be regarded as an improved version of DDR2. They have many similarities, mainly using 144Pin spherical pin FBGA packaging. However, the DDR3 core has been improved: the DDR3 video memory uses 0.11 μ m Production process The power consumption is significantly lower than that of DDR2. In addition, DDR3 video memory uses "Pseudo Open Drain" Interface technology , as long as the voltage is appropriate, Display chip DDR3 video memory can be directly supported. of course, Phanerophore Longer delay time (CAS latency) has always been a common problem of high frequency video memory, and DDR3 is no exception. The CAS latency of DDR3 is 5/6/7/8, compared with 3/4/5 of DDR2. Objectively speaking, compared with DDR2, DDR3 has not made rapid progress in technology, but its performance advantages are still obvious: (1) power consumption and Calorific value Smaller: learned lessons from DDR2 Control costs On the basis of, it reduces energy consumption and heat generation, making DDR3 easier to be accepted by users and manufacturers. (2) Higher operating frequency: Due to lower energy consumption, DDR3 can achieve a higher operating frequency, which to some extent makes up for the disadvantage of longer delay time. At the same time, it can also be one of the selling points of the video card, which has been shown in the video card with DDR3 video memory. (3) Reduce the overall cost of graphics card: DDR2 Phanerophore The specifications are mostly 4M X 32bit, and the 128MB video memory commonly used with high-end video cards requires 8. The DDR3 video memory is mostly 8M X 32bit, and the single particle size is large. Four of them can form 128MB video memory. In this way, the PCB area of the graphics card can be reduced, and the cost can be Effective control In addition, when the number of particles is reduced, the video memory power consumption can be further reduced. (4) Good versatility: Compared with DDR changing to DDR2, DDR3 has compatibility Better. because Pin , packaging and other key features remain unchanged, and the DDR2 Show Core and Public edition The designed graphics card can use DDR3 video memory with a little modification, which is beneficial to manufacturers to reduce costs. At present, DDR3 appears to exist New Most of the high-end graphics cards have been widely used.

GDDR5

Video storage picture

GDDR5 (Graphics Double Data Rate, version 5) SDRAM is application program A type of high-performance DRAM video memory designed for high frequency bandwidth requirements. Like the previous version（ GDDR4 ）GDDR5 DDR2 SDRAM With double speed DDR3 SDRAM However, GDDR5 also has an 8-bit wide prefetch cache similar to GDDR4.

Now? Samsung and Qimonda GDDR5 has started Development plan 。 Samsung Electronics From the third quarter, 5000/3200 Mibps GDDR5 video memory will be taken out. This video memory adopts 170FBGA packaging, GDDR5x32 512Mbit G-Die process, and the working voltage is 1.5v. From the end of this year to the beginning of next year, 1Gb GDDR5 video memory with GDDR5x32170FBGA specification, D-Die process and 1.5v working voltage will be produced. Qimonda is also expected to pilot produce GDDR5 video storage at the end of this year, and put it into mass production in the first quarter of next year.

Today, GDDR3 is the type of video memory commonly equipped on video cards, and GDDR4 is only a few high-end models. Qimonda, which is determined to develop by leaps and bounds, has trial produced the world's first GDDR5.

Performance capacity

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Video memory

Memory capacity It's a video card Upper Local The capacity of video memory, which is one of the key parameters for selecting video card. The size of video memory capacity determines the temporary video memory Store data To some extent, it will also affect the performance of the graphics card. With the development of video card, the video memory capacity is gradually increasing, and there is a growing trend. The video memory capacity has grown from 512KB, 1MB, 2MB and other small capacities in the early days to 64MB, 128MB, 256MB, 512MB, 768MB, until the current mainstream 2GB, 4GB, 6GB and high-end video cards 8GB, 16GB, 32GB. Some professional video cards even have 48GB video memory. stay Maximum resolution of graphics card On the other hand, the maximum resolution is directly related to the video memory to some extent, because the data of these pixels are initially stored in the video memory, so the video memory capacity will affect the maximum resolution. When the video memory capacity of the early video card was only 512KB, 1MB, 2MB and so on, the video memory capacity was really a bottleneck of the maximum resolution; But at present, the video memory capacity of mainstream video cards, even 64MB, has been eliminated. The mainstream entertainment video cards have reached 512MB or 1GB, and some professional video cards even have 4GB of video memory. In this case, the video memory capacity is no longer a factor affecting the maximum resolution. In terms of graphics card performance Display chip The processing capacity of the 3D Games And professional rendering requires more and more data to be temporarily stored, and the required video memory capacity is also increasing. To some extent, the video memory capacity will also affect the performance of the video card. For example, when the display core is strong enough and the video memory capacity is small, there is a large amount of texture mapping data to be stored. If the video memory capacity is not enough to store these data, the display core will only be idle for some time to wait for the completion of these data processing, which affects the performance of the display core and thus the performance of the video card. It is worth noting that the larger the video memory capacity is, the higher the performance of the video card is not necessarily, because the three factors that determine the performance of the video card are the first one used Display chip , followed by video memory bandwidth (which depends on the video memory bit width and Memory frequency ）, and finally the video memory capacity. The proper video memory capacity of a video card is determined by its use Display chip That is to say, it is reasonable that the video memory capacity should match the performance of the display core. The higher the performance of the display chip, the higher the processing capacity, the larger the video memory capacity should be. However, the low performance display chip with large capacity video memory does not help its performance. For example, some commercially available video storage devices with 512MB large capacity Radeon In terms of graphics card performance, the 9550 graphics card is better than the Radeon 9550 graphics card with 128MB video memory Core frequency and Memory frequency The parameters are the same, because the relatively low processing capacity of the Radeon 9550 display core determines that it is meaningless to equip it with a large capacity video memory. On the contrary, the large capacity video memory also brings about the problem of increased purchase costs.

data

Data bit refers to the number of bits that can be transmitted within a clock cycle. It is an important factor that determines the video memory bandwidth and is closely related to the performance of the video card. When video storage Same kind And when the operating frequency is the same, the larger the number of data bits, the higher its performance. The calculation method of video memory bandwidth is: Operating frequency × Data bandwidth/8. Taking the current GeForce3 video card as an example, its video memory system bandwidth=230MHz × 2 (multiplied by 2 because DDR video memory is used) × 128/8=7.36GB.

Data bit is a very important parameter of video memory and video card. On the graphics card working process Medium, Z Buffer 、 Frame buffer And texture buffers will consume video memory bandwidth resources significantly. Bandwidth is 3D chip Compared with the data volume standard transmitted by the local memory, the video memory capacity is not important at this time, nor will it affect the bandwidth. There is little difference in performance between 64MB and 32MB video cards with the same video memory bandwidth. Because the bottleneck of the system is the video memory bandwidth Pixel Shader When working, insufficient video memory bandwidth will cause data transmission congestion, resulting in Display chip Waiting affects speed. Video memory is mainly divided into 64 bit and 128 bit. Under the same operating frequency, the bandwidth of 64 bit video memory is only half of that of 128 bit video memory. This is why the performance of Geforce2 MX200 (64 bit SDR) is far inferior to that of Geforce2 MX400 (128 bit SDR).

Memory interface

Video memory

The bit width of video memory is the number of bits of data that can be transmitted by video memory within a clock cycle. The larger the number of bits, the larger the amount of data that can be transmitted instantly. This is one of the important parameters of video memory. At present, there are three kinds of video memory bit widths in the market: 64 bit, 128 bit and 256 bit. The 64 bit video card, 128 bit video card and 256 bit video card are the corresponding video memory bit widths. The higher the bit width of video memory, the better the performance and the higher the price. Therefore, 256 bit wide video memory is more used in high-end video cards, while 128 bit video memory is basically used in mainstream video cards. As you know, video memory bandwidth= Memory frequency X video memory bit width/8, the video memory bit width will determine the video memory bandwidth when the video memory frequency is the same. For example, the same Memory frequency It is 500MHz 128 bit and 256 bit video memory, so the video memory bandwidth of the two will be respectively: 128 bit=500MHz * 128 ／ 8=8GB/s, and 256 bit=500MHz * 256 ／ 8=16GB/s, which is twice the 128 bit. It can be seen that the importance of video memory bit width in video memory data. The video memory of the video card is composed of video memory chips Bit width Also by Phanerophore The bit width of,. Video memory bit width= Phanerophore Bit width × number of display particles. Phanerophore There are memory numbers of relevant manufacturers on the Internet. You can find their numbers on the Internet to find out Bit width , and then multiply by the number of video memory particles to get the bit width of the video card. This is the most accurate method, but it is troublesome to implement. Here's a simple one, but it is only suitable for general conditions. There are some special cases, and it can be applied in most cases. At present, there are mainly two packaging forms of video memory: TSOP and BGA. Generally, the video memory packaged with BGA is 32 bits/chip, while the video memory packaged with TSOP is 16 bits/chip/ . If the graphics card uses four BGA packaged video memories, its Bit width It is 128 bit. If eight TSOP packaging particles are used, the bit width is 128 bit. However, if only four TSOP packaging particles are used in the graphics card, the video memory bit width is only 64 bit. This is just a general technique, not necessarily suitable for all situations. To make the most accurate judgment, you'd better check the video memory number!

bandwidth

Video memory bandwidth is Display chip The larger the bandwidth, the faster the communication between the display chip and the video memory. To indicate this width, the unit of video memory bandwidth is: bytes/second. The bandwidth of video memory and its Bit width And the speed of video memory (that is, the working frequency). The final conclusion: video memory bandwidth=video memory bit width × Memory frequency /8。 The speed of video memory is generally in ns, and the common video memory is 6ns, 5.5ns, 5ns, 4ns, 3.8ns, up to 1.8ns. The corresponding operating frequencies are 143MHz, 166MHz, 183MHz, 200MHz, 250MHz and up to 550MHz. The calculation method of operating frequency is very simple - Video memory speed The reciprocal of is the rated operating frequency of video memory, such as Clock cycle If it is 4ns, the operating frequency of this video memory is 1/4ns=250MHz (if it is DDR video memory, multiply the result by 2).

Video memory capacity= Display resolution × Number of color bits/8 bit.

For example, if the display resolution is 1024x768 and the number of color bits is 32bit, the required video memory capacity=1024x768x32bit/8bit=3145728 byte , but this is for 2D graphics card (ordinary plane), if it is 3D accelerator card , the required video memory capacity is 1024x768x32bitx3/8bit=9437184byte=9.216MB, which is the minimum requirement, and a certain amount of capacity must be added as texture display memory , otherwise, when the display resource is fully occupied, the computer will only Main memory As texture memory, such a second call will result in Display performance As a real 3D accelerator, its video memory capacity must be greater than 9.216MB. The video memory of workstation video card is more than 64MB. For example, 2D drawing applications, even in the case of 1600x1200, can be up to 1600x1200x32bit/8bit=7680000byte=7.5MB. For 3D drawing applications, such as 3D Studio Max , then the capacity requirement is 7.5x3=22.5MB, but this is the minimum requirement, so 32MB video memory is used to cope with this kind of 2D Video playback of drawing or entertainment, general 3D design 。 For workstations, since they run larger software and larger operations, the video memory is more than 256M.

Basic knowledge

The speed of video memory is generally in ns. Common video memories include 7ns, 6ns, 5.5ns, 5ns, 4ns and even 3.8ns. The corresponding rated operating frequencies are 143MHz, 166MHz, 183MHz, 200MHz and 250MHz. Rated operating frequency=1/video memory speed. Of course, for some high-quality video memories, there is a certain margin for the actual maximum operating frequency of video memories. The overclocking of video memory is based on this principle, as shown in Rated frequency 6ns video memory exceeds the operating frequency of 190MHz. Here we will also talk about the actual operating frequency and the equivalent operating frequency of video memory. DDR video memory can transmit data on both the rising and falling edges of the clock clock frequency and Data bits In the case of width, the video memory bandwidth is twice that of ordinary SDRAM. In other words, the actual working frequency of DDR video memory is normal when the video memory speed is the same SDRAM video memory 2 times. Similarly, the bandwidth of DDR video memory is twice that of ordinary SDRAM video memory. For example, the working frequency of 5ns SDRAM video memory is 200MHZ, while the equivalent working frequency of 5ns DDR video memory is 400MHZ. But it should be understood that when the video card is manufactured, the manufacturer has set the actual working frequency of the video memory, and the actual working frequency is not necessarily equal to the maximum frequency of the video memory. This kind of situation is more common now. For example, the video memory can work at 650 MHz at most, but the operating frequency of the video card is set to 550 MHz during manufacturing, and there is a certain overclocking space in the video memory. This is also the method commonly used by manufacturers at present. The selling point of video card is overclocking.

list

The video memory used for the video card is also called the memory used for the motherboard DDR 、 DDR2 、 DDR3 、 DDR4 However, due to the large difference in specification parameters, they cannot be used universally. Therefore, video memory types are also divided into GDDR, GDDR2, GDDR3, GDDR4 and mainstream GDDR5.

Frequency corresponding to video memory speed corresponds to DDR frequency

6NS 166MHZ 333MHZ

5NS 200MHZ 400MHZ

4NS 250MHZ 500MHZ

3.6NS 278MHZ 556MHZ

3.3NS 300MHZ 600MHZ

2.8NS 360MHZ 720MHZ

2.2NS 450MHZ 900MHZ

2NS 500MHZ 1000MHZ

Memory frequency

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Memory frequency It refers to the frequency when the display is stored on the video card by default MHz (megahertz). Memory frequency To some extent, it reflects the speed of the video memory. Memory frequency It varies with the type and performance of video memory, SDRAM video memory They usually work at a lower frequency, usually 133MHz and 166MHz, Memory frequency , mainly in Medium and low end graphics card Used on, DDR2 video memory Due to high cost and average performance, the usage is not large. DDR3 video memory It is the most widely used high-end graphics card Video memory type 。 Different video memories can provide Memory frequency There are also great differences, mainly including 400MHz, 500MHz, 600MHz, 650MHz, and 800MHz, 1200MHz, 1600MHz, and even higher in high-end products.

Video memory frequency vs Video memory clock cycle Is related, and they are in reciprocal relationship, that is, video memory frequency=1/video memory Clock cycle 。 If it is SDRAM If the clock cycle of video memory is 6ns, its Memory frequency 1/6ns=166 MHz. For DDR SDRAM perhaps DDR2 、 DDR3 , its clock cycle is 6ns, then its Memory frequency 1/6ns=166 MHz, but it is important to know that this is the DDR SDRAM Actual frequency Instead of what we usually say DDR video memory Frequency. Because DDR transmits data in both the rising and falling periods of the clock, it transmits data twice a cycle, which is twice the SDRAM frequency. The habitually called DDR frequency is its equivalent frequency working frequency Multiply by 2 to get the equivalent frequency. Therefore, 6ns DDR video memory Memory frequency 1/6ns * 2=333MHz. For details, see the introduction of various video memories below. However, it should be understood that when the video card is manufactured, the manufacturer has set the actual working frequency of the video memory, and the actual working frequency is not necessarily equal to the maximum frequency of the video memory. This kind of situation is common. For example, the video memory can work at 650 MHz at the maximum, but the operating frequency of the video card is set to 550 MHz at the time of manufacturing Overfrequency Space. This is the usual method used by manufacturers. The video card sells on overclocking. GDDR3 。

Video memory package

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Video memory package Means Phanerophore Adopted Packaging technology Type, packaging is to wrap the video memory chip to avoid contact with the outside world and prevent damage to the chip from the outside world. Impurities and undesirable gases in the air, even steam Will corrode the precision circuit on the chip, and then cause the electrical performance to decline. Different packaging technologies differ greatly in manufacturing processes and processes Memory chip The exertion of its own performance also plays a vital role. Video memory Packaging form Mainly QFP 、 TSOP -II、 MBGA TSOP-II and MBGA are common. TSOP-II was widely used in early SDRAM and DDR video memory, but now with Video memory speed As a result, more and more video memories use MBGA packaging, especially DDR2 and DDR3 video memories, which all use MBGA packaging. In addition, many manufacturers also refer to the packaging of DDR2 and DDR3 video memory as FBGA , this kind of address is more focused on Pin The naming of the arrangement is actually the same packaging form. In addition, compared with TSOP-II, MBGA can achieve higher Memory frequency However, it is not easy to think that the video memory packaged with MBGA must be better than the video memory, because whether it is easy to overclock depends more on the difference between the default frequency agreed by the factory and the actual frequency that the video memory can reach, including the design and manufacture of the video card. Simply speaking, the video memory packaged with MBGA can reach a higher frequency, but its default frequency is also higher.

QFP

QFP It is the abbreviation of Package, which means "small square plane package". QFP package It is frequently used on early video cards, but few QFP packaged video memory with a speed of more than 4ns. Because of the problems of process and performance, it has been gradually used by TSOP-II and BGA Replaced by. The QFP package has pins around the particles, which can be clearly identified. TSOP-II (Thin Small Out Line Package). TSOP package Make pins around the chip, and use SMT Technology（ Surface mounting technology ）Directly attached to PCB board Surface. TSOP package Overall dimension Parasitic parameters (when the current changes significantly, the output Voltage disturbance ）It is small, suitable for high-frequency applications, easy to operate, and high reliability. At the same time, TSOP package has Yield It is high and cheap, so it is widely used. TSOP packaging is the most widely used Video memory package Type. TSOP-II package pins are on both sides of the video memory.

MBGA

MBGA Refers to micro Ball grid array package , the full English name is Micro Ball Grid Array Package. It is connected with TSOP Memory chip Different from that, the pins of MBGA are not exposed, but parasitic at the bottom of the chip in the form of tiny solder balls, so the pins cannot be seen in this video memory. The advantages of MBGA are Noise Less, good heat dissipation Electrical performance Good, can connect more feet, and can improve Yield 。 The most prominent reason is that the internal components have smaller spacing Transmission delay Small, which can greatly improve the frequency. The most prominent feature is the smaller spacing of internal components Transmission delay Short, which can greatly improve the frequency. Compared with TSOP packaged video memory, MBGA video memory has excellent performance. But it also puts forward requirements for circuit wiring. The former only needs 66Pin, and the lead is very long, and they are all lying on the PCB board, so it is relatively easy to design, weld, process and detect; The area of the latter is only about 1/4 of that of the former, but it has 144Pin. Each Pin is tiny Tin ball It is much more difficult to design and produce. In the early days, many SDRAM and DDR video memories used TSOP-II. Now, with the improvement of video memory speed, more and more video memories use MBGA packaging, especially DDR2 and DDR3 video memories, which all use MBGA packaging. In addition, many manufacturers also use DDR2 and DDR3 Video memory package It is called FBGA, which is more focused on the naming of the pin arrangement. It is actually the same packaging form.

Clock cycle

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Video memory Clock cycle Is video storage Clock pulse As a measure of Video memory speed Important indicators. The faster the video memory speed is, the greater the amount of data exchanged per unit time is. In the same case, the performance of the video card will be significantly improved. The clock cycle of video memory is generally in ns（ nanosecond ）Is the unit, and the operating frequency is in MHz Is the unit. Video memory clock cycle Follow working frequency One-to-one correspondence , the relationship between them is: working frequency=1 ÷ clock cycle × 1000. that Memory frequency If it is 166MHz, its clock cycle is 1 ÷ 166 × 1000=6ns. about DDR SDRAM perhaps DDR2 、 DDR3 video memory For example, the equivalent is used to describe its operating frequency output frequency 。 Because it can Rising edge and Falling edge Can transmit data, so when the operating frequency and Data bits With the same width, Video memory bandwidth yes SDRAM Twice as much. In other words, the equivalent output frequency of DDR SDRAM video memory is twice that of SDRAM video memory when the video memory clock cycle is the same. For example, the working frequency of 5ns SDRAM video memory is 200MHz, while the equivalent working frequency of 5ns DDR SDRAM or DDR2 and DDR3 video memory is 400MHz. Common video memory clock cycles are 5ns, 4ns, 3.8ns, 3.6ns, 3.3ns, 2.8ns, 2.0ns, 1.6ns, 1.1ns, or even lower.

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