Memory module

Computer components

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Memory module is CPU A computer component that can be addressed through the bus and read and write. Memory module in personal computer Historically Main memory Extension of. With the continuous update of computer software and hardware technology, memory module has become the whole read-write memory. What we usually call computer memory（ RAM ）Is the total memory module capacity.

The memory module is an essential part of the computer, and the CPU can data bus yes memory addressing 。 Historically, there was main memory on the computer motherboard, and the memory module was an expansion of the main memory. In the future, there will be no main memory on the computer motherboard, and the CPU will completely rely on the memory module. All External storage The content on must pass through memory to function.

Chinese name: Memory module
Foreign name: RAM
Category: computer
Interpretation: Computer components for reading and writing

Full English name: Random-Access Memory
Full Chinese name: Random access memory
Storage principle: from trigger Store data
Unit structure: Six tube NMOS or OS composition
Access speed: Fastest of all access devices

developing process

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be born

At first, the computer used blocks of memory IC , we must weld them to mother board It can be used normally only when it is installed. Once a memory IC is broken, it must be soldered down before it can be replaced. This is too laborious. Later, computer designers invented modular strip memory, each of which was integrated with multiple memory ICs. Accordingly, they designed Memory socket In this way, the memory module can be disassembled at will. Since then, the maintenance and expansion of memory become very convenient.

development

Memory chip The state of "" has been used until the early days of 286. In view of its disadvantages of being unable to disassemble and replace, this has caused a realistic obstacle to the development of computers. In view of this, memory module came into being. Solder the memory chip to the pre designed Printed circuit board On the computer motherboard Memory socket 。 In this way, the problem that memory is difficult to install and replace is completely solved.

Before the 80286 motherboard was released, the world didn't pay much attention to the memory. At that time, the memory was directly solidified on the motherboard, and the capacity was only 64~256KB. For the working programs run by the PC at that time, the performance and capacity of this memory were enough to meet the requirements of that time software program Processing needs. However, with the emergence of software programs and the new generation of 80286 hardware platform, programs and hardware have higher requirements for memory performance. In order to improve speed and expand capacity, memory must be independent Packaging form As a result, the concept of "memory module" was born.

When the 80286 motherboard was just launched, the memory module used SIMM (Single In lineMemory Modules, unilateral contact Memory module ）Interface, 30pin, 256kb capacity, 8 chips Data bits And 1 piece Check bit It forms a bank. Because of this, the 30 pin SIMM we see usually uses four together. Since the PC entered the civil market in 1982, the 30 pin SIMM memory with 80286 processor is the originator of the memory field.

Then, from 1988 to 1990, PC technology ushered in another development peak, namely the 386 and 486 times CPU It has developed to 16bit, so 30pin SIMM memory can no longer meet the demand Memory bandwidth It has become a bottleneck that needs to be solved urgently, so 72pin SIMM memory appears at this time. 72pin SIMM supports 32bit fast Page Mode Memory and memory bandwidth have been greatly improved. The capacity of a single 72pin SIMM memory is generally 512KB~2MB, and only two are required to be used at the same time. Because it is incompatible with the 30pin SIMM memory, the PC industry resolutely eliminated the 30pin SIMM memory at this time.

EDO memory module produced by IBM and CANDA

EDO DRAM （Extended Date Out RAM , external expansion Data mode storage ）Memory, which is a popular memory module between 1991 and 1995. EDO-RAM is the same as FP DRAM Very similar, it cancels the extension data output Memory and transfer memory Storage cycle Between time interval , putting Data transmission The next page is accessed while the CPU is given, so the speed is 15~30% faster than ordinary DRAM. working voltage It is 5V in general, 32bit in bandwidth, and over 40ns in speed. It is mainly used in the 486 and early Pentium On the computer.

From 1991 to 1995, we saw an embarrassing situation: memory technological development It is relatively slow and almost stagnates, so we can see that EDO RAM 72 pin and 168 pin coexist. In fact, EDO memory also belongs to the category of 72 pin SIMM memory, but it uses a new Addressing mode 。 EDO has made breakthroughs in cost and capacity. With the rapid development of manufacturing technology, the capacity of a single EDO memory has reached 4~16MB. Due to Pentium and higher CPU Data bus width Both are 64bit or higher, so EDO RAM and FPM RAM must be used in pairs.

SDRAM memory module

SDRAM times

From Intel Celeron series and AMD K6 Processor and related Mainboard chipset After the launch, the performance of EDO DRAM memory can no longer meet the needs. Memory technology must be thoroughly innovated to meet the needs of the new generation of CPU architecture. At this time, memory began to enter the classic SDRAM era.

The first generation SDRAM memory is PC66 specification, but soon due to Intel and AMD The debate over the frequency of the CPU fsb The PC66 memory was soon replaced by the PC100 memory when it was upgraded to 100MHz. With the PIII of 133MHz external frequency and the advent of the K7 era, the PC133 specification further improved the overall performance of SDRAM in the same way, and the bandwidth was increased to more than 1GB/sec. Since the SDRAM bandwidth is 64bit, which corresponds to the CPU's 64bit data bus width, it only needs one memory to work, and its convenience is further improved. In terms of performance, its input and output signals are kept synchronized with the external frequency of the system, so the speed is significantly higher than the EDO memory.

It is undeniable that the SDRAM memory has developed from the early 66MHz to the later 100MHz and 133MHz. Although the bottleneck problem of memory bandwidth has not been completely solved, the CPU Overfrequency It has become an eternal topic for DIY users, so many users will consider the PC100 brand with good brand Memory overclocking To 133MHz for CPU overclocking Success, it is worth mentioning that in order to facilitate some overclocking user demand Some PC150 and PC166 memory specifications have appeared in the market.

Although the bandwidth of SDRAM PC133 memory can be increased to 1064MB/S, plus Intel has started the latest Pentium 4 So the SDRAM PC133 memory cannot meet the future development needs. At this time, Intel monopolistic market And Rambus in PC Marketing Rambus DRAM Memory (called RDRAM Memory). Different from SDRAM, it adopts a new generation of high-speed simple memory architecture, based on a kind of RISC (Reduced Instruction Set Computing, Reduced instruction set computer ）Theory, which can reduce the complexity of data system performance Improved.

In the competition between AMD and Intel, this is the era of frequency competition, so this is the time of CPU Dominant frequency In order to surpass AMD, Intel launched high-frequency PentiumⅢ As well as Pentium 4 processor, Rambus DRAM memory is regarded by Intel as its own competitive trump card in the future. Rambus DRAM memory is high clock frequency To simplify each Clock cycle Therefore, the memory bandwidth is excellent. For example, the PC 1066 1066 MHz 32 bits bandwidth can reach 4.2G Byte/sec. Rambus DRAM was once considered a perfect match for Pentium 4.

Nevertheless, Rambus RDRAM Memory was born at an untimely time. Later, it would still be "plundered" by higher speed DDR. At that time, Rambus RDRAM memory of PC600 and PC700 appeared due to Intel 820 Chipset The "error event" and PC800 Rambus RDRAM made the Pentium 4 platform high because of the high cost, which could not be popular with the public users. All kinds of problems made Rambus RDRAM dead. Rambus had hoped to have PC1066 RDRAM with higher frequency to turn the tide, but finally it was in front of DDR memory.

DDR era

DDR memory module

DDR SDRAM (Dual DataRate SDRAM) is called DDR for short, which means "double rate SDRAM". DDR is an upgraded version of SDRAM clock signal Rising edge And Falling edge Data is transmitted once each, which makes the DDR Data transmission speed It is twice the traditional SDRAM. Since only the falling edge signal is used, it will not increase the energy consumption. As for location and control signal It is the same as the traditional SDRAM, and only transmits at the rising edge of the clock.

DDR memory is a compromise solution between performance and cost, which aims to quickly establish a solid Market space , and then step by step on the frequency, and finally make up for the lack of memory bandwidth. The first generation DDR200 specification has not been popularized, and the second generation PC266 DDR SRAM (133MHz clock × 2 times data transmission =266MHz bandwidth) is derived from PC133 SDRAM memory, which brings DDR memory to the first climax. In addition, many Celeron and AMD K7 processors are using DDR266 Specification of memory, and its subsequent DDR333 Memory is also a transition, and DDR400 Memory has become the current mainstream platform option, Dual channel DDR400 memory has become the basic standard for 800FSB processor collocation, and the subsequent DDR533 specification has become the object of choice for overclocking users.

DDR2 times

DDR2 (Double Data Rate 2) SDRAM is created by JEDEC (Electronic Equipment engineering Joint Commission) technical standard , which is different from the previous generation DDR memory The biggest difference between the technical standards is that although the basic mode of data transmission is used at the same time when the clock goes up/down, the DDR2 memory has twice the pre read capacity of the previous generation of DDR memory (that is, 4bit data read prefetch). In other words, each clock of DDR2 memory can External bus And can read/write data internally Control bus Run at 4 times the speed.

In addition, the DDR2 standard stipulates that all DDR2 memories use FBGA Packaging form, which is different from the widely used TSOP /TSOP-II packaging form, FBGA package Can provide better Electrical performance With heat dissipation, it provides a solid foundation for the stable operation of DDR2 memory and the development of future frequency. Recall the development of DDR, from the first generation application to personal computer Through DDR266, DDR333 to dual channel DDR400 technology, the development of the first generation of DDR has reached the technical limit, and it is difficult to improve the working speed of memory through conventional methods; With the development of Intel's latest processor technology, Front end bus The requirement for memory bandwidth is getting higher and higher, with higher and more stable Operating frequency DDR2 memory will be the general trend.

With the continuous improvement of CPU performance, our requirements for memory performance are also gradually upgraded. It is undeniable that the DDR that only increases bandwidth based on high frequency will be unable to do so sooner or later. Therefore, JEDEC organization has been brewing DDR2 standards for a long time LGA775 The 915/925 interface and the latest 945 and other new platforms begin to support DDR2 memory, so DDR2 memory will begin to define the memory field.

DDR2 can provide a bandwidth of at least 400MB/s per pin on the basis of 100MHz transmission frequency, and its interface will operate at 1.8V, thus further reducing the Calorific value To increase the frequency. In addition, DDR2 will be integrated into CAS, OCD, ODT and other new technologies performance index and Interrupt instruction , improving memory bandwidth Utilization 。 From JEDEC organizer According to the DDR2 standard, DDR2 memory for PC and other markets will have different clock frequencies of 400, 533 and 667MHz. The high-end DDR2 memory will have 800 and 1000 MHz frequencies. DDR-II memory will use 200 -, 220 -, 240- Pin FBGA packaging form. The initial DDR2 memory will be 0.13 μ m Production process ， Memory granule The voltage is 1.8V, and the capacity density is 512MB.

Memory technology will have no suspense in 2005, represented by SDRAM Static memory It will not be popularized in five years. QBM It is also hard to recover the declining trend with RDRAM memory, so the era of coexistence of DDR and DDR2 will be an absolute fact.

Besides PC-133, VCM (VirXual Channel Memory) is also an important successor of PC-100. VCM“ virtual channel Memory ", which is also a memory standard supported by most newer chipsets. VCM memory is mainly manufactured according to a" cache DRAM "technology developed by NEC, which integrates" channel cache " register Configure and control. While realizing high-speed data transmission, VCM also maintains a high level of traditional SDRAM compatibility Therefore, VCM memory is usually called VCM SDRAM. The difference between VCM and SDRAM is that no matter whether the data is processed by CPU or not, it can be submitted to VCM for processing first, while ordinary SDRAM can only process the data processed by CPU, so VCM is better than SDRAM Processing data 20% faster. There are many chipsets that can support VCM SDRAM, including Intel's 815E VIA 694X, etc.

RDRAM

After Intel introduced PC-100, due to the development of technology, the 800MB/s bandwidth of PC-100 memory can no longer meet the demand, while the bandwidth of PC-133 has not increased significantly (1064MB/s), which also can not meet the future development demand. In order to monopolize the market, Intel and Rambus jointly promote Rambus DRAM (DirectRambus DRAM) in the PC market, as shown in Figure 4-3.

Rambus DRAM is a memory specification first proposed by Rambus Company. It adopts a new generation of high-speed simple memory architecture, which can reduce the complexity of data and improve the performance of the whole system. Rambus uses a 400MHz 16bit bus. In a clock cycle, it can transmit data at the rising edge and falling edge at the same time Actual speed It is 400MHz × 2=800MHz, and the theoretical bandwidth is (16bit × 2 × 400MHz/8) 1.6GB/s, equivalent to twice of PC-100. In addition, Rambus can also store 9bit bytes. The extra bit is reserved and may be used later as: ECC (ErroI · Checking and Correction) check bit. Rambus clock can reach 400MHz, and only 30 copper wires are used for connection Memory controller and RIMM (Rambus In line MemoryModules, Rambus embedded Memory module ）, reducing the length and number of copper wires can reduce the electromagnetic interference To quickly improve the memory working frequency 。 However, at high frequencies, the heat emitted will definitely increase, so the first Rambus memory even needs to come with its own Cooling fan 。

DDR3 times

Difference between memory ddr, ddrii and ddr3

Compared with DDR2, DDR3 has a lower working voltage, which drops from 1.8V of DDR2 to 1.5V, providing better performance and power saving; The 4 bit read ahead of DDR2 is upgraded to 8 bit read ahead. DDR3 can reach a maximum speed of 2400Mhz. Since the fastest DDR2 memory speed has been increased to 800Mhz/1066Mhz, the first batch DDR3 memory The module will take off from 800Mhz. stay Computex In the grand exhibition, we saw several memory manufacturers exhibit 1333Mhz DDR3 modules.

New design adopted by DDR3 based on DDR2:

1.8bit prefetching design, while DDR2 is 4bit prefetching, so the DRAM core frequency is only 1/8 of the interface frequency, and the core operating frequency of DDR3-800 is only 100MHz.

2. Adoption Point to point To ease the communication between address/command and Control bus The burden of.

3. Adopt the production process below 100nm, reduce the working voltage from 1.8V to 1.5V, and add the asynchronous reset and ZQ calibration functions.

DDR4 times

DDR4 Memory will have two specifications. The DDR4 memory using the single ended Signaling signal transmission speed It has been confirmed to be 1.6~3.2Gbps, but based on Differential signal The transmission rate of DDR4 memory of the technology will reach 6.4Gbps. Thanks to a DRAM It is basically impossible to realize two interfaces, so there will be two types of DDR4 memory products based on traditional SE signals and differential signals.

According to the introduction of several relevant personnel in the semiconductor industry, DDR4 memory will coexist in the way of Single ended Signaling (traditional SE signal) and Differential Signaling (differential signaling technology). It is expected that these two standards will launch different chip products, so in the era of DDR4 memory, we will see two incompatible memory products

Main differences

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The difference between DDR2 and DDR

Compared with DDR, DDR2 The main improvements are Memory module At the same speed, it can provide DDR memory Twice the bandwidth. This is mainly through the efficient use of two DRAM Core. In contrast, only one DRAM core can be used for DDR memory on each device. Technically, DDR2 still has only one DRAM core in its memory, but it can be accessed in parallel and process four data instead of two in each access.

And double speed operation Data buffer In combination, DDR2 memory realizes Clock cycle It can process up to 4 bits of data, twice as much as the 2 bits of data that can be processed by traditional DDR memory. Another improvement of DDR2 memory is that it uses FBGA package The mode replaces the traditional TSOP mode.

However, although DDR2 memory uses the same DRAM core speed as DDR, we still need to use a new motherboard to match DDR2 memory, because the physical specifications of DDR2 are incompatible with DDR. First, the interface is different. DDR2 Pin The number is 240 pins, while the DDR memory is 184 pins; Secondly, the VDIMM voltage of DDR2 memory is 1.8V, which is also different from 2.5V of DDR memory.

Before we understand many new technologies of DDR2 memory, let's look at a set of data comparing DDR and DDR2 technologies.

1. Delay problem:

It can be seen from the above table that, in the same Core frequency Next, the actual DDR2 working frequency Double the DDR. This is due to the fact that DDR2 memory has four BIT pre read capabilities that are twice as large as standard DDR memory. In other words, although DDR2 and DDR both adopt the same method of performing the rising delay and falling delay of the clock at the same time data transmission But DDR2 has twice the ability of pre reading system command data as DDR. That is to say, under the same operating frequency of 100MHz Actual frequency 200MHz, while DDR2 can reach 400MHz.

Another problem arises: in DDR and DDR2 memory with the same operating frequency, the memory latency of the latter is slower than that of the former. For example, DDR 200 and DDR2-400 have the same latency, while the latter has twice the bandwidth. In fact, DDR2-400 and DDR 400 have the same bandwidth, which is 3.2GB/s, but DDR400 The core operating frequency of DDR2-400 is 200MHz, while the core operating frequency of DDR2-400 is 100MHz, which means that the delay of DDR2-400 is higher than that of DDR400.

2. Encapsulation and Calorific value ：

The biggest breakthrough of DDR2 memory technology does not lie in the transmission capacity that users think is twice that of DDR, but in the use of lower heat output low power consumption In this case, DDR2 can achieve faster frequency increase, breaking the 400MHZ limit of standard DDR.

DDR memory is usually TSOP Chip packaging forms, such as Packaging form It can work well at 200MHz. When the frequency is higher, its too long pin will produce high impedance and Parasitic capacitance , which will affect its stability and the difficulty of frequency increase. This is why the core frequency of DDR is difficult to break through 275MHZ. DDR2 memory uses FBGA package Form. Unlike the widely used TSOP packaging, FBGA packaging provides better Electrical performance With heat dissipation, it provides a good guarantee for the stable operation of DDR2 memory and the development of future frequency.

DDR2 The memory uses 1.8V voltage, which is much lower than the DDR standard of 2.5V, thus providing significantly smaller power consumption and heating capacity. This change is significant.

New technologies adopted by DDR2:

In addition to the above differences, DDR2 also introduces three new technologies, namely OCD, ODT and Post CAS 。

OCD (Off Chip Driver): also known as offline drive adjustment, DDR II can improve signal integrity through OCD. DDR II is pulled up through adjustment（ pull -Up)/Pull down the resistance value to make the two voltages equal. Use OCD to improve signal integrity by reducing the tilt of DQ-DQS; adopt control voltage To improve the signal quality.

ODT: ODT is the end of the built-in core resistor 。 We know that using DDR SDRAM To prevent data line Terminal reflection signals require a large number of terminating resistors. It greatly increases the Manufacturing cost 。 In fact, different Memory module The requirements for the termination circuit are different. The size of the termination resistance determines the signal ratio and reflectivity If the terminal resistance is small, the signal reflection of the data line is low, but Signal-to-noise ratio Also lower; If the termination resistance is high, the signal to noise ratio of the data line is high, but the signal reflection will also increase. Therefore, the terminating resistor on the motherboard cannot match the memory module very well, and it will also affect the signal quality to a certain extent. DDR2 can build proper terminating resistance according to its own characteristics, which can ensure the best signal waveform. Using DDR2 can not only reduce the cost of motherboard, but also get the best signal quality, which is incomparable to DDR.

Post CAS : It is set to improve the utilization efficiency of DDR II memory. In the Post CAS operation, the CAS signal (read/write/command) can be inserted into a clock cycle after the RAS signal, and the CAS command can remain valid after the additive delay. customary tRCD (RAS to CAS and delay) is replaced by AL (Additive Latency), which can be set in 0, 1, 2, 3, 4. Since the CAS signal is placed one clock cycle after the RAS signal, the ACT and CAS signals will never collide.

In general, DDR2 has adopted many new technologies and improved many shortcomings of DDR. Although it has many shortcomings such as high cost, slow latency, it is believed that with the continuous improvement and perfection of technology, these problems will eventually be solved.

Main differences between DDR3 and DDR2

1． Burst length （Burst Length，BL）

because DDR3 The prefetch of is 8bit, so Burst transmission The Burst Length (BL) is also fixed to 8. For DDR2 and early DDR architecture systems, BL=4 is also commonly used. For this reason, DDR3 adds a 4bit Burst Chop mode, that is, a BL=4 read operation plus a BL=4 write operation compose a BL=8 data burst transmission, which can then be transmitted through A12 Address line To control this burst mode. It should also be noted that any sudden interruption operation will DDR3 memory It is prohibited and not supported by, but replaced by more flexible emergencies Transmission control (e.g. 4bit sequential burst).

2. Addressing timing

Just as the number of delay cycles increases after DDR2 changes from DDR, the CL cycle of DDR3 will also be improved compared with DDR2. The CL range of DDR2 is generally between 2 and 5, while DDR3 is between 5 and 11, and the design of additional delay (AL) has also changed. In DDR2, the range of AL is 0~4, while in DDR3, AL has three options, namely 0, CL-1 and CL-2. In addition, DDR3 also adds a new timing parameter - write delay (CWD), which will depend on the specific operating frequency.

3. DDR3's new reset function

Reset is an important new function of DDR3, and a pin is specially prepared for this purpose. The DRAM industry has long required this feature to be added, but now it is finally implemented on DDR3. This pin will simplify the initialization of DDR3. When the Reset command is valid, the DDR3 memory will stop all operations and switch to the least active state to save power.

During Reset, DDR3 memory will shut down most internal functions, all data receivers and transmitters will be shut down, all internal program devices will be reset, DLL (delay Phase-locked loop ）And Clock circuit Will stop working and ignore data bus Any movement on. In this way, DDR3 will achieve the goal of saving the most power.

4. DDR3 adds ZQ calibration function

ZQ is also a new pin, which is connected with a 240 ohm low tolerance reference resistor. This pin is automatically verified through a command set and an On Die Calibration Engine (ODCE) data output Driver On resistance And ODT. After the system sends this command, it will recalibrate the on resistance and ODT resistance with corresponding clock cycles (512 clock cycles after power on and initialization, 256 clock cycles after exiting the self refresh operation, and 64 clock cycles in other cases).

5． reference voltage Divide into two

In the DDR3 system, the reference voltage signal VREF, which is very important for the memory system, will be divided into two signals, namely VREFCA for command and address signals and VREFDQ for data bus, which will effectively improve the signal noise level of the system data bus.

6． Point to point connection （Point-to-Point，P2P）

This is to improve system performance The important changes made are also a key difference between DDR3 and DDR2. In a DDR3 system, one Memory controller It only works with one memory channel, and this memory channel can only have one socket. Therefore, between the memory controller and the DDR3 memory module Point to point (P2P) relationship (single physical Bank Or point to two point (P22P) relationship (module of dual physical bank), which greatly reduces the load of address/command/control and data bus. In terms of memory module, it is similar to the type of DDR2, but there are also standards DIMM (desktop PC) SO-DIMM /Micro-DIMM（ Notebook computer ）、 FB-DIMM 2 (servers), of which the second generation FB-DIMM will use AMB2 (advanced memory Buffer ）。

7. Number of logical banks

DDR2 In SDRAM, there are 4 banks and 8 banks designed to meet the demand of future high-capacity chips. DDR3 is likely to start with 2Gb capacity, so there will be 8 logical banks at the beginning. In addition, it is also ready for 16 logical banks in the future.

8. Automatic self refresh (SRT, Self-Refresh Temperature）

To ensure that the saved data is not lost, DRAM must be refreshed regularly, and DDR3 is no exception. However, in order to maximize power savings, DDR3 uses a new automatic self refresh design (ASR, Automatic Self-Refresh）。 When ASR is started, a Temperature sensor To control the refresh frequency because refresh frequency If high, Power extinction The higher the temperature, the higher the temperature. The temperature sensor should minimize the refresh frequency and reduce the working temperature 。 However, the ASR of DDR3 is an optional design. It is not likely that DDR3 memory in the market supports this function. Therefore, an additional function is the self refresh temperature range (SRT, Self-Refresh Temperature）。 Pass Mode register Two temperature ranges can be selected, one is the general temperature range (such as 0 ℃ to 85 ℃), and the other is the extended temperature range, such as the maximum temperature of 95 ℃. For the two temperature ranges set internally by DRAM, DRAM will refresh at a constant frequency and current.

9. Local self refresh (RASR, Partial Array Self-Refresh）

This is an option of DDR3. With this function, the DDR3 memory chip can refresh only part of the logical Bank, rather than all of it, so as to minimize the self refresh Power consumption 。 This is similar to the design of Mobile DRAM.

10. Packages

DDR3 has some new functions, so its pins will be increased. The 8bit chip uses 78 ball FBGA package, the 16bit chip uses 96 ball FBGA package, and DDR2 has 60/68/84 ball FBGA package. And the DDR3 must be green sealed and cannot contain any Hazardous substances 。

The 64 bit architecture oriented DDR3 obviously has more advantages in frequency and speed. In addition, due to its automatic self refresh based on temperature, local self refresh and other functions, DDR3 is also much better in power consumption. Therefore, it may be the first Mobile Devices Just like the server, not the desktop, was the first to welcome DDR2 memory. stay CPU external frequency The future of DDR3 is also bright in the field of PC desktops, which has been promoted most rapidly. Intel will launch a new chip - Bear Lake, which will support DDR3 specification, while AMD It is also expected to support both DDR2 and DDR3 on the K9 platform.

Memory asynchronous working mode It has a variety of meanings. In a broad sense, the memory working frequency and CPU Of fsb Inconsistency can be called memory asynchrony Operating mode 。 First, the earliest memory asynchronous working mode appeared in the early a main board Chipset The memory can work at 33MHz higher or 33MHz lower than the external frequency of the CPU (note that the difference is only 33MHz), which can improve the system memory The performance may allow the old memory to continue to play waste heat. Secondly, in the normal operating mode (CPU does not Overfrequency ）A lot Mainboard chipset Memory asynchronous working mode is also supported, such as Intel 910GL The chipset only supports 533MHz FSB, that is, 133MHz CPU external frequency, but it can work with 133MHz DDR 266, 166MHz DDR 333, and 200MHz DDR 400 (note that the CPU external frequency 133MHz is 66MHz different from the working frequency 200MHz of the DDR 400), but the performance is different with different memories. Again, on CPU overclocking In order not to drag the CPU Overclocking capability At this time, the working frequency of the memory can be lowered to facilitate overclocking, such as AMD's Socket 939 Interfaced Opteron 144 It is very easy to overclock, and the external frequency of many products can easily exceed 300MHz. However, if in the memory synchronization mode, the equivalent frequency of the memory will be as high as DDR 600, which is obviously impossible. In order to successfully exceed the 300MHz external frequency, we can set the memory to DDR 333 or DDR 266 in the motherboard BIOS before overclocking. After exceeding the 300MHz external frequency, The former is only DDR 500 (some excellent memory can reach it), and the latter is only DDR 400 (completely normal Standard frequency ）It can be seen that the memory is set correctly Asynchronous mode It is helpful to the success of overclocking.

Almost all motherboard chipsets support memory asynchrony, Intel The company supports from 810 series to the newer 875 series, while VIA has provided this function since 693 chipset.

performance index

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Memory performance indicators

There are four performance indicators to evaluate the memory module:

(1) Storage capacity: that is, one memory module can hold Binary information content For example, the storage capacity of commonly used 168 line memory modules is generally 32 MB, 64 MB and 128 MB. DDRII3 is generally 1GB to 8GB.

(2) Access speed (storage cycle): the shortest time required between two independent access operations, also called storage cycle, Semiconductor memory Of Access cycle It is generally 60 nanoseconds to 100 nanoseconds.

(3) Memory reliability: used for memory reliability Mean time between failures It can be understood as the average time interval between two failures.

(4) Price performance ratio Performance mainly includes memory capacity, storage cycle and reliability. The performance price ratio is a comprehensive indicator, and different memories have different requirements.

Purchasing comments

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In addition to the number of pins, capacity and Access speed In addition, the following factors should also be considered:

(1) Parity

In order to ensure the memory access data accuracy Some memory modules have parity bits, such as a 3-chip or 9-chip memory module. If you have high requirements for the accuracy of computer operation, you'd better choose Parity Memory module for the function.

(2) Price

Although the price of the new version memory module has dropped significantly compared with the old version memory module, there are still some differences in the price of different brands and performance. You can choose the price that suits you according to your needs and budget. In addition, you should also pay attention to the brand and quality when purchasing memory. There are many manufacturers producing memory, and the brands with more reliable quality are: South Korea LG 、 Kingston , Japanese Toshiba , Seiko Nippon Electric Corporation Panasonic, Japan.

Memory plays an important role in computers. Memory generally adopts semiconductor Storage unit , including Random access memory （RAM）， read-only memory (ROM), and Cache （CACHE）。 Just because RAM is the most important memory.

Generally speaking, memory refers to computer system RAM in.

Common problems and solutions

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I believe that many friends will encounter various problems in one way or another when using computers. For example, when the computer fails to start normally, cannot access the operating system or run application software, and often crashes for no reason, these problems occur Regular meetings The operation failed due to an abnormal memory failure. This is because the memory is used in the computer Three major pieces As one of the accessories, it is mainly responsible for temporary data access. However, the quality of memory modules on the market is uneven, so the probability of failure is high. In order to solve these common memory problems, I will give you some advice. I hope it can help you.

The memory problem is partly due to the upgrade of memory, but due to the mismatch of memory types, we often encounter some problems. The specific memory problems and countermeasures are as follows.

1. Unable to start normally

Tips: There are three main ways to solve this kind of problem: first, replace the memory location, which is the simplest and most commonly used method. Generally, the low-speed old memory is inserted at the front. Second, on the premise that the machine can be basically powered on, enter BIOS settings, and set the settings related to memory according to the specifications of low-speed memory. For example, use one of the memory (if DDR333 and DDR400 are used together, it is better to use DDR333 memory), start the computer, enter BIOS settings, and set the working frequency and reaction time Slow down. The old memory can stable operation The second memory can be inserted after shutdown.

2. The computer is unstable

Tips: This kind of problem is mainly caused by memory compatibility. The basic solution is the same as above. First, change the memory location. Second, turn off the memory in the BIOS SPD The option of automatic configuration is changed to manual configuration. Third, if the motherboard has I/O Voltage regulation Function, the voltage can be properly raised to enhance the stability of the memory.

3. Memory capacity identification is incorrect after mixed plugging

Tips: The first reason for this phenomenon may be the main board chipset itself. Some old mainboards only support 256MB of memory (i815 series only supports 512MB), and the excess cannot be identified and used. Of course, there are some cases because the motherboard cannot support high memory particles. The only way to solve these problems is to replace the motherboard or memory. In addition, in some cases, by adjusting the memory Insert Order This problem can also be solved.

The problem of unstable memory intermixing is an old one. Faced with this situation, the author suggests that you should choose the memory module like Kingston 、 Jintaike These high-quality memories, because of their excellent electrical compatibility and stability, have a lower probability of problems, and are also guaranteed after sales.

The other part is because memory is in use, Goldfinger Slot with motherboard poor contact Cause or hit Viruses The specific memory problems and countermeasures are as follows.

4. The computer cannot start normally

The chassis alarm horn appears for a long time after the computer host is powered on Short sound It beeps, or the computer can start up but cannot enter the operating system normally after the host power is turned on, and the screen shows "Error: Unable to ControlA20 Line" error message Rear parallel crash.

Tips: Most of the above failures are caused by the poor contact between the memory slot and the motherboard. processing method After opening the chassis, pull out the memory and wipe the memory with alcohol and clean paper towel Goldfinger And memory socket, and check whether there is any sign of damage to the memory socket. Reinsert the memory after the wiping inspection. Generally, the problem can be solved. If the machine still cannot be started, pull out the memory and insert it into another memory socket for testing. If the problem still exists at this time, the memory has been damaged. At this time, only a new memory module can be replaced.

5. The power on display is "ON BOARD PARLTY ERROR"

Tips: There are three possible reasons for this phenomenon. First, CMOS The middle parity check is set as valid, but there is no parity check bit on the memory module. Second, the parity check circuit on the motherboard is faulty. Third, the memory module is damaged or in poor contact. To solve the problem, first check the relevant items in CMOS, and then reinsert the memory module for a try. If the fault still persists, the parity check circuit on the motherboard is faulty. Replace the motherboard.

6. Problems occurred when running the application software in DOS state

Tips: This kind of failure is generally caused by the conflict between software allocation and memory occupation Black screen 、 blurred screen , crash, the best solution is to exit the Windows operating system DOS State.

7. Windows runs significantly slower

Tips: The system displays many prompts about memory errors. This kind of fault is generally caused by windows Running under application program Illegal access to memory, too many unnecessary plug-ins, applications Active window Too many applications are opened configuration file Unreasonable and other reasons can make the system speed Slower , or even crash. This fault must be solved by removing some illegal plug-ins (such as 3721), memory Resident program , reduce the active window and adjust the profile（ INI ）If the speed obviously slows down when running a program, it can be solved by reinstalling the application. If the system slows down when running any application software or program, the best way is to reinstall the operating system.

8. The memory is infected by a virus program and resides in the memory

The size of the memory value in the CMOS parameter is modified by a virus, resulting in the inconsistency between the memory value and the actual memory size of the memory module, and the phenomenon of slower speed and system crash when using.

Support: use the latest Anti-Virus The software performs a comprehensive anti-virus treatment on the system, and thoroughly cleans all viruses in the system. Because CMOS has been viral infection Therefore, the CMOS can be recovered by discharging Default 。 The method is to discharge the CMOS in short circuit, restart the machine, and carefully check all items after entering the CMOS Hardware parameters , correctly set the Parameter value 。

9. The computer selects a memory module that is incompatible with the motherboard

Tips: Before upgrading the computer's memory module, you must carefully check the motherboard's instructions. If the motherboard does not support 512M or more of large memory, it will not work even after the upgrade. If the motherboard supports the problem caused by poor compatibility of the motherboard, you can upgrade the BIOS of the motherboard to see if the compatibility problem can be solved.

Design difficulties

There are many high-speed signals, and there are many isometric lines with strict requirements;

because PCB board There are many layers, and the signal rate is high, Stack And parameter plane design.

Function classification

Announce

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Function of memory

Memory module

Memory is computer（ PC 、 singlechip ）An essential component. And dispensable External storage Different, the memory is a component that reads and writes in the bus mode; Memory is more than just starting data warehouse Role of. In addition to a few essential programs in the operating system that reside permanently in memory, we usually use programs such as Windows Linux System software, including typing software, game software, etc Data It is placed on tape, disk, optical disk, removable disk and other external storage devices, but any data in external storage can be used only after being transferred into memory. Any type of input on the computer (from external storage, keyboard, mouse Microphone 、 Scanner , etc.) and any kind of output (display, printing, audio and video, writing to external memory, etc.) can only be carried out through memory.

Memory classification

DDR memory module

Memory is divided into DRAM And ROM, the former is also called Dynamic random access memory One of its main features is that the data will be lost after power failure, which is what we usually refer to as memory; The latter is also called read-only memory The first thing we usually start is the one stored in the ROM on the motherboard BIOS Program, and then it calls Windows in the hard disk. One of the main features of ROM is that data will not be lost after power failure.

According to the number of pins on the memory module, we can divide the memory module into 30 lines, 72 lines, 168 lines, etc. thirty Line and The 72 line memory module is also called the single memory module SIMM Goldfinger Both provide the same signal memory structure.) 168 line memory module is also called dual rank memory module DIMM 。 The 30 line memory module is no longer available; In the first two years, the popular type is the 72 line memory module, with the capacity of 4 megabytes, 8 megabytes, 16 megabytes and 32 megabytes; The mainstream variety in the market is 168 line memory module. The capacity of 168 line memory module generally includes 16 megabytes, 32 megabytes, 64 megabytes, 128 megabytes, and so on. Generally, it is OK to plug in a computer, but only based on VX, TX, and BX Chipset The motherboard only supports 168 line memory modules.

EDO and SDRAM

Previously, we have divided memory modules into 30, 72 and 168 lines according to the number of pins. In fact, they have essential differences in structure and performance.

Details of memory installation

For example, a 72 line memory module is a EDO memory The mainstream 168 line memory modules are almost all SDRAM Memory; EDO memory Access speed Basically maintained at about 60 nanoseconds, capable of adapting to 75 megabytes hertz But running 83 MHz is a bit difficult; The access speed of SDRAM memory can generally reach about 10 nanoseconds, and it can adapt to external frequencies above 100 MHz. Therefore, since the end of 1997, EDO memory has been gradually replaced by SDRAM. Up to now, almost no one has used EDO to install computers. Only when upgrading and expanding the memory of old computers can we still use it.

In fact, EDO memory is replaced by SDRAM Inevitability Because the dominant frequency of mainstream CPUs in the market has reached 2GHz, the dominant frequency of CPUs will be higher and higher in the future. However, because the reading and writing speed of the traditional memory module can't keep up with the speed of the CPU, the CPU is forced to insert and wait Instruction cycle , which greatly reduces the overall performance of the computer. In order to alleviate this memory bottleneck problem, we must adopt a new memory structure, namely SDRAM 。 Because, in theory, SDRAM and CPU frequency Sync, share one Clock cycle 。 SDRAM contains two interleaved Storage array When the CPU accesses data from one storage array, the other is ready to read and write data. Through tight switching between the two storage arrays, the reading efficiency is doubled. The storage speed of the latest SDRAM has reached 5 nanoseconds, so SDRAM has become the mainstream of memory development.

Memory module

Of course, EDO memory did not completely surrender. On the contrary, with its excellent Video Features And low price display memory Such fields are still successful in succession, and many low-end graphics cards are without exception using EDO memory. In addition, many hard disks, optical drives and printers also use EDO cache. It can be seen that EDO memory is really a valuable tool!

RAM Some are like the blackboard in the classroom. The teacher keeps writing on the blackboard during class Erase 。 RAM requires continuous power supply at all times, or data will be lost. If the RAM data is not lost after the power is turned off, you can ensure that the computer is in the last shutdown state every time you turn on the computer, instead of having to restart the computer and turn it on again every time application program Has. But RAM requires constant power supply. Is there any way to solve this problem? With the progress of technology, people have come up with a way to supply a small amount of power to RAM to keep the RAM data from losing. This is the standby function of the computer, especially in Win2000. The power supply is connected when sleeping, but it consumes a small amount of power.

According to the interface form of memory module, there are two common memory modules: single in line memory module (SIMM) and dual in line memory module (DIMM). The SIMM memory module is divided into 30 lines and 72 lines. Compared with SIMM memory module, the pins of DIMM memory module are increased to 168 lines. DIMMs can be used alone, and different capacities can be mixed. SIMMs must be used in pairs.

According to the working mode of memory, the memory can also be in the form of FPA EDO DRAM and SDRAM (synchronous dynamic RAM).

Thinkpad original memory module

FPM (FAST PAGE MODE) RAM fast page mode Random access memory : This is earlier computer system Common memory, every three Clock pulse Data is transmitted once a cycle.

EDO（EXTENDED DATA OUT）RAM

extend data output Random access memory: EDO memory cancels the time interval between two storage cycles of the mainboard and memory, and it outputs data every two clock pulse cycles, greatly reducing the Access time To increase storage speed by 30%. EDO is generally 72 pins, and the EDO memory has been replaced by SDRAM.

S（ synchronous ）DRAM

Synchronous dynamic random access storage : SDRAM is 168 pin, which is the memory used by PENTIUM and above models. SDRAM locks CPU and RAM together through the same clock, so that CPU and RAM can share a clock cycle and work synchronously at the same speed Clock pulse The rising edge of starts to transmit data, Speed ratio EDO memory increased by 50%.

DDR（DOUBLE DATA RATE）RAM

SDRAM is an updated product that allows data transmission on the rising and falling edges of the clock pulse, so that the speed of SDRAM can be doubled without increasing the clock frequency.

Memory module

RDRAM (RAMBUS DRAM) memory bus dynamic random access memory; RDRAM is a new DRAM developed by RAMBUS with system bandwidth and chip to chip interface design frequency range Data is transmitted through a simple bus. He also uses low voltage signals to transmit data along both sides of the high-speed synchronous clock pulse. INTEL will add support for RDRAM to its 820 chipset product.

There are two main memory parameters: storage capacity And access time. The larger the storage capacity, the more information the computer can remember. The access time is nanosecond (NS) is calculated in units. One nanosecond is equal to one billionth of a second. The smaller the number, the faster the memory is accessed.

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