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Memory

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One of the important components in the computer
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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.
Memory is an important part of a computer, also known as memory and Main memory , which is used to temporarily store the calculation data in the CPU, as well as the hard disk External memory Data exchanged. It is External storage And CPU As a bridge for communication, all programs in the computer run in memory. The strength of memory performance affects the overall performance of the computer. As soon as the computer starts running, the operating system will transfer the data to be calculated from the memory to the CPU for calculation. When the calculation is completed, the CPU will send the results.
The running of memory determines the overall running speed of the computer.
Memory module from Memory chip 、 Circuit board 、 Goldfinger And other parts. [1]
Chinese name
Memory
Foreign name
Memory
Alias
Memory
Belonging to
Computer supporting hardware
Interface type
DIP、 SIMM 、DIMM
Technical indicators
Memory capacity, access time, delay

catalog

  1. one Product Introduction
  2. two development
  3. ▪ Memory module
  4. ▪ SDRAM
  5. ▪ DDR era
  6. ▪ DDR2 era
  7. ▪ RDRAM era
  8. ▪ DDR3 era
  9. ▪ DDR4 era
  1. ▪ Second generation HBM3
  2. three classification
  3. ▪ Classification according to working principle
  4. ▪ Classified by memory technology standard
  5. ▪ Classification by system logic
  6. ▪ Other types
  7. four Interface type
  8. ▪ DIP
  9. ▪ SIMM
  1. ▪ DIMM
  2. five Technical indicators
  3. ▪ Parity
  4. ▪ Memory capacity
  5. ▪ Access time
  6. ▪ CL delay
  7. ▪ frequency
  8. ▪ bandwidth
  9. six Purchasing method
  1. ▪ The workmanship should be excellent
  2. ▪ SPD Hidden Information
  3. ▪ Counterfeit repaired products
  4. seven Troubleshooting
  5. eight Common misunderstandings
  6. ▪ Internal and external memory
  7. ▪ Memory card capacity

Product Introduction

Announce
edit
Memory
Memory is an important part of the computer structure. It is used for Stored program And data.
For computers, only with memory can there be memory function To ensure normal operation.
There are many kinds of memory. It can be divided into Main memory and Auxiliary memory Main memory is also called internal memory (memory for short), Hong Kong and Taiwan be called Memory ）。 [2]
Memory is also called main memory. It is CPU can Direct addressing Of storage space , by semiconductor device make. It is characterized by fast access rate.
Memory is the main part of the computer External storage For.
Programs we usually use, such as: Windows operating system , typing software, game software, etc. Generally installed on hard disk External storage However, their functions cannot be used only for this purpose. They must be transferred into memory to run in order to really use their functions.
We usually input a paragraph of text or play a game, but it is actually in memory. It's like in a study, the bookshelf for storing books and Bookcase Computer equivalent External storage The desk we work on is equivalent to memory.
Usually, we will keep a large amount of data storage stay External storage Put some temporary or small amount of data and programs in memory. Of course, the quality of memory will directly affect the computer running speed 。 [2]
Memory is a place to temporarily store programs and data. When we use WPS When you process a document, when you type a character on the keyboard, it is stored in memory. When you choose to save, the data in the memory will be saved to the hard (magnetic) disk. [2]

development

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Computer didn't exist in the early days Memory module The concept of. The earliest memory was arranged on the line in the form of magnetic cores transistor A constituent Bistable circuit As one bit (BIT) memory.
Every bit must have Corn grain For size, it can be imagined that a machine room can only hold a capacity of no more than 100 k bytes. Later came the integration soldered on the motherboard Memory chip , providing direct support for computer operations in the form of memory chips.
At that time Memory chip The capacity is very small. The most common ones are 256K × 1bit and 1M × 4bit. Even so, it was more than enough for computing tasks at that time. [3]

Memory module

Memory chip The state of ". In view of its disadvantages of being unable to be disassembled and replaced, this has caused a realistic obstacle to the development of computers.
In view of this, Memory module Then came into being. take Memory chip Welding to pre designed Printed circuit board On the computer motherboard, the memory socket is also used. In this way, the problem that memory is difficult to install and replace is completely solved. [3]
Before the 80286 motherboard was released, the world didn't pay attention to memory. At this time, the memory is directly solidified on the motherboard, and the capacity is only 64-256KB. For the working program run by PC at that time, the performance and capacity of this memory are enough to meet the software program Processing needs.
With the emergence of software programs and the new generation 80286 hardware platform, programs and hardware put forward higher requirements for memory performance. In order to improve speed and expand capacity, the memory must be Packaging form Appeared, and thus was born“ Memory module ”The concept of. [3]
When the 80286 motherboard was first introduced, Memory module Adopted SIMM (Single In lineMemory Modules, unilateral contact Memory module ）Interface, 30pin, 256kb capacity, 8 chips Data bits And a check bit to form a bank.
Because of this, the 30pin 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 ancestor of the memory field. [3]
Then, in the middle of 1988~1990, PC technology ushered in another development peak, namely the 386 and 486 times. At this time, the CPU has developed to 16bit, so the 30pin SIMM memory can no longer meet the demand Memory bandwidth It has become a bottleneck that needs to be solved urgently, so the 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 memories are required to be used at the same time. Because it is not compatible with 30pin SIMM memory, the PC industry resolutely eliminated 30pin SIMM memory at this time. [3]
EDO DRAM (Extended Date Out RAM external expansion Data mode Memory, which was popular between 1991 and 1995 Memory module 。 EDO DRAM is the same as FPM DRAM (Fast Page Mode RAM) is very similar. It cancels expansion data output Memory and transfer memory Storage cycle Between time interval , putting Data transmission Go to the next page while giving CPU access.
Therefore, 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. [3]
From 1991 to 1995, memory technological development Relatively slow, almost stagnant. We can see that 72 pin and 168 pin EDO DRAM coexist. In fact EDO memory It also belongs to the category of 72pin SIMM memory.
But it uses a brand new Addressing mode 。 EDO has made breakthroughs in cost and capacity, relying on the rapid development of manufacturing technology. Now single EDO memory The capacity of has reached 4~16MB. Due to Pentium and higher CPU Data bus width Both are 64bit or higher, so EDO DRAM and FPM DRAM must be used in pairs. [3]

SDRAM

From Intel Celeron series and AMD K6 Processor and related Mainboard chipset After the introduction, 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. [3]
first generation SDRAM Memory is PC66 specification, but soon due to Intel and AMD The debate over frequency will CPU external frequency It is upgraded to 100MHz. So the PC66 memory was soon replaced by the PC100 memory. Then, with the advent of the 133MHz external frequency PIII and 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, because its input and output signals are kept synchronized with the external frequency of the system, the speed is significantly higher than the EDO memory. [3]
SDRAM memory has developed from 66MHz in the early days to 100MHz and 133MHz later. Although the bottleneck problem of memory bandwidth has not been completely solved CPU overclocking It has become an eternal topic for DIY users.
Many users consider PC100 as a good brand Memory overclocking To 133MHz for CPU overclocking success. In order to facilitate the needs of some overclocking users, some PC150 and PC166 memory specifications have appeared in the market. [3]
The bandwidth of SDRAM PC133 memory can be increased to 1064MB/S. In addition, Intel has started the latest Pentium 4 Therefore, SDRAM PC133 memory cannot meet future development needs.
In order to achieve 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. [3]
In the competition between AMD and Intel, this is the era of frequency competition. At this time, the CPU Dominant frequency Continuous improvement, Intel introduced high-frequency in order to surpass AMD PentiumⅢ And Pentium 4 processors.
Rambus DRAM memory is regarded by Intel as its own competitive trump card in the future. Rambus DRAM memory high clock frequency To simplify each Clock cycle The amount of data and memory bandwidth were excellent at that time. For example, the bandwidth of PC 1066 1066 MHz 32 bits can reach 4.2G Byte/sec. Rambus DRAM was once considered a perfect match for Pentium 4. [3]
Rambus RDRAM memory was born out of time, and it will still be "robbed" by higher speed DDR. At that time, the Rambus RDRAM memory of PC600 and PC700 appeared Intel 820 Chipset The "error event" and PC800 Rambus RDRAM made the Pentium 4 platform superior due to the high cost, and could not win the popularity of the public users.
All kinds of problems have killed Rambus RDRAM. Rambus hoped that the PC1066 RDRAM with higher frequency could turn the tide, but he finally succumbed to DDR memory. [3]

DDR era

DDR SDRAM (Double Data Rate SDRAM) is called DDR for short, which also means "double rate SDRAM".
DDR can be said to be an upgraded version of SDRAM. DDR in clock signal Rising edge And the falling edge, so that the DDR Data transmission speed It is twice the traditional SDRAM.
Since only the falling edge signal is used, the energy consumption will not increase. As for location and control signal It is the same as the traditional SDRAM, and only transmits at the rising edge of the clock. [3]
DDR memory As a compromise solution between performance and cost, its purpose is 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 PC133SDRAM memory. It brings DDR memory to the first climax.
In 2017, many Celeron and AMD K7 processors were using DDR266 memory, and its later DDR333 memory was also a transition. DDR400 memory has become the 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. [3]

DDR2 era

With the continuous improvement of CPU performance, the requirements of the public on memory performance have gradually increased.
DDR that increases bandwidth based on high frequency will be unable to do so sooner or later, so JEDEC The organization has been brewing DDR2 standards for a long time, plus 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 today's memory field. [3]
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 commands, lifting Memory bandwidth Utilization of. 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 Of FBGA Packaging form.
The initial DDR2 memory will be 0.13 μ m Production process The voltage of memory particles is 1.8V, and the capacity density is 512MB. [3]
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. [3]
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 based on NEC It is a "cache DRAM" technology developed by the company. It integrates the "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.
At present, there are many chipsets that can support VCM SDRAM, including Intel's 815E, VIA's 694X, etc. [3]

RDRAM era

After Intel introduced PC-100, the 800MB/s bandwidth of PC-100 memory cannot meet the greater demand due to the development of technology. However, the bandwidth improvement of PC-133 is not significant (1064MB/s), which also cannot meet the future development needs.
In order to achieve the goal of monopolizing the market, Intel and Rambus Company jointly promote Rambus DRAM (DirectRambus DRAM) in the PC market. [3]
Rambus DRAM is a memory specification first proposed by Rambus Company. It adopts a new generation of high-speed simple memory architecture and is based on a RISC (Reduced Instruction Set Computing) theory, which can reduce the complexity of data and improve the performance of the entire system.
Rambus uses a 400MHz 16bit bus Clock cycle You can transmit data at the same time as the rising edge and falling edge, so that its 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. An additional bit is reserved and may be used as ECC (ErroI Checking and Correction) check bit in the future. 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 increase the working frequency of memory.
However, at high frequencies, the heat emitted will definitely increase, so the first Rambus memory even needs to come with its own Cooling fan 。 [3]

DDR3 era

DDR3 Compared with DDR2, it 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.
At present, DDR3 can reach a maximum speed of 2000Mhz, although the fastest DDR2 Memory speed The speed has been increased to 800Mhz/1066Mhz, but DDR3 memory The module will still take off from 1066Mhz. [3]
New design adopted by DDR3 based on DDR2: [3]
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 Topology architecture to ease 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. Some manufacturers have introduced 1.35V low-voltage DDR3 memory. [3]

DDR4 era

In 2012, DDR4 The era will open, the working voltage will be reduced to 1.2V, and the frequency will be increased to 2133MHz. The next year, the voltage will be further reduced to 1.0V, and the frequency will be 2667MHz.
New generation DDR4 Memory will have two specifications. According to the introduction of several relevant personnel in the semiconductor industry, DDR4 memory will be Single -EndedSignaling (traditional SE signal) DifferentialSignaling（ Differential signal Technology). among AMD Mr. Phil Hester of the company also confirmed this.
Now there are 3200Mhz ddr4 and 4266Mhz ddr4 LPDDR4
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. [3]

Second generation HBM3

In July 2023, Micron announced that it had sampled the industry's first 8-layer stacked 24GB second-generation HBM3 memory, based on 1 β The DRAM process node high bandwidth memory (HBM) solution has a bandwidth of more than 1.2TB/s and a pin rate of more than 9.2Gb/s, which can improve the performance of the existing HBM3 solution by up to 50%. Meguiar introduced that the second generation HBM3 product has 2.5 times more performance per watt than the previous generation, which can help shorten the training time of large language models (such as GPT-4 and higher) and reduce the total cost of ownership (TCO). [8]

classification

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edit
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. (synchronous) SDRAM synchronous dynamic random access memory: SDRAM has 168 pins, which is the memory used by PENTIUM and above.
SDRAM locks CPU and RAM together through the same clock, so that CPU and RAM can share a Clock cycle , working synchronously at the same speed, each Clock pulse The rising edge of starts to transmit data, Speed ratio EDO memory Increase by 50%.
DDR (DOUBLE DATA RATE) RAM: an updated version of SDRAM Clock pulse The rising and falling edges of the SDRAM are used to transmit data, so that the speed of SDRAM can be doubled without increasing the clock frequency. [4]

Classification according to working principle

● read-only memory （ROM）
ROM representation read-only memory (Read Only Memory). When a ROM is manufactured, information (data or programs) is stored and permanently saved. These information can only be read, and generally cannot be written. Even if the machine is powered off, these data will not be lost.
ROM is generally used to store basic programs and data of the computer, such as BIOS ROM. Its physical shape is generally DIP Integrated block 。 [4]
Now popular read-only memory yes Flash Memory (Flash Memory), which belongs to EEPROM ( Electrically Erasable Programmable Read Only Memory ）The upgrade of can be rewritten repeatedly through electrical principles. Now most BIOS programs are stored in the FlashROM chip. USB drive and Solid state hard disk (SSD) is also made using the principle of flash memory. [4]
● Random access memory （RAM）
Memory
Random Access Memory means that data can be read from or written to. When the machine is powered off, the data stored in it will be lost.
We usually buy or upgrade Memory module It is used as the memory of the computer. The memory module (SIMM) is a small piece of RAM integrated blocks Circuit board , which is inserted into the Memory socket To reduce the space occupied by the RAM integrated block. Common Memory module There are 4G, 8G, 16G, 32G, etc.
RAM is divided into two types: DRAM and SRAM. [4]
  1. one
    DRAM ( Dynamic RAM， Dynamic random access memory ）The storage unit of is capacitance It is made with related components. The amount of charge stored in the capacitor represents signals 0 and 1. The capacitor has leakage, and insufficient charge will cause Storage unit Data error, so DRAM Periodic refreshes are required to maintain the state of charge. DRAM has a simple structure and high integration, and is usually used to manufacture memory chips in memory modules. [4]
  2. two
    SRAM ( Static RAM， SRAM ）The storage unit of is transistor And related components Latch , each Storage unit It has the function of locking "0" and "1" signals. It is fast and does not require a refresh operation, but has poor integration and high power consumption. It is usually used to create CPU caches with small capacity but high efficiency. [4]
● Cache memory （Cache）
Cache is also a concept we often encounter, which is what we usually see L1 cache （ L1 Cache ）、 L2 Cache （L2 Cache）、 L3 cache （ L3 Cache ）These data, located between the CPU and the memory, is a faster read/write memory than the memory. When the CPU writes or reads data into the memory, the data is also stored in the Cache memory Medium. When the CPU needs these data again, the CPU will Cache memory Read data instead of accessing slower memory. Of course, if the required data is not in the Cache, the CPU will read the data in memory again. [4]

Classified by memory technology standard

According to memory technology standards, it can be divided into SDRAM ， DDR SDRAM ， DDR2 SDRAM and DDR3 SDRAM 。 [4]
1) SDRAM
(Synchronous Dynamic RAM , Sync Dynamic random access memory ）3.3V working voltage is adopted, and the memory data bit width is 64 bits. SDRAM and CPU pass the same clock frequency Lock them together to make them work synchronously at the same speed. SDRAM transmits data on the rising edge of each clock pulse SDRAM The memory golden finger is 168 feet. [4]
SDRAM The memory includes the following types: PC66/100/133150/166, Core frequency 66MHz, 100Mz133MHz, 150MHz and 166MHz respectively. clock frequency , equivalent frequency is equal to core frequency SDRAM The maximum memory data transmission bandwidth is 166MHz × 64bit ÷ 8=1.3GB/s. [4]
Related concepts
  • Core frequency : is the working frequency of the storage unit inside the memory granule, that is, the refresh frequency of the capacitor. It is the basic frequency of memory operation, and other frequencies are based on it. [4]
  • clock frequency : Also called memory bus frequency, it is the working frequency provided by the clock chip of the motherboard to the memory. [4]
  • Equivalent frequency: also called equivalent data transmission frequency, it is the actual frequency of data exchange between memory and outside. Usually, the equivalent efficiency is pasted on the memory label. [4]
2) DDR SDRAM
(Double data rate SDRAM, double rate synchronization Dynamic random access memory ）The 2.5V working voltage is adopted, and the memory data bit width is 64 bits. One DDR SDRAM (DDR memory for short) Clock pulse Transfer data twice, respectively in Clock pulse The rising edge and falling edge of are transmitted once respectively, so it is called double rate SDRAM. [4]
DDR Memory golden fingers are 184 feet. DDR memory includes the following types: DDR 200/266/333/400/500. Core frequency And clock frequency The equivalent frequencies are 100 MHz, 133 MHz, 166 MHz, 200 MHz and 250 MHz respectively, and the equivalent frequencies are 200 MHz, 266 MHz, 333 MHz, 400 MHz and 500 MHz respectively. Please note that, DDR The equivalent frequency of memory is clock frequency Because DDR memory works at double rate. The DDR memory core adopts 2-bit data pre reading, that is, 2-bit data is taken at a time (one pulse). [4]
The DDR memory core frequency is equal to clock frequency , the equivalent frequency is clock frequency So that the number of memory cores retrieved at one time (one pulse) can be transmitted in a timely manner. The maximum data transmission bandwidth of a single DDR memory is 500 MHz × 64 bit 8-4 GB/s. [4]
3) DDR2 SDRAM
(Double Data Rate 2 SDRAM ）1.8V working voltage , the memory data bit width is 64 bits. DDR2 memory is the same as DDR memory. One clock pulse transmits data twice, but DDR2 But it has twice the memory of the previous generation DDR The pre read capability of memory, that is, 4-bit data pre read. [4]
DDR 2 Memory golden finger is 240 feet. DDR2 The memory includes the following types: DDR2 533/667/800/1066. The core frequencies are 133 MHz, 166 MHz, 200 MHz and 266 MHz respectively, the clock frequencies are 266 MHz, 333 MHz, 400 MHz and 533 MHz respectively, and the equivalent frequencies are 533 MHz, 667 MHz, 800 MHz and 1066 MHz respectively. [4]
As has been said before, DDR2 The memory core adopts 4-bit data pre reading, that is, four bits are taken at a time (one pulse). If it is the same as the previous generation of DDR memory, clock frequency If it is equal to the core frequency and the equivalent frequency is twice the clock frequency, it is impossible to output the extracted data in time; So DDR 2 memory clock frequency It is twice the core frequency, so that the number taken from the memory core in the same time interval can be transmitted in the same time interval. [4]
Single root DDR2 The data transmission bandwidth of the memory is up to 1066 MH2z X 64 bit 8 - 8.6 GB/s. [4]
4) DDR3 SDRAM
(Double Data Rate 3 SDRAM ）Use 1.5 V working voltage , the memory data bit width is 64 bits. Similarly, DDR3 memory has twice the pre read capacity of the previous generation DDR2 memory, that is, 8-bit data pre read. [4]
For DDR 3 memory, the following relationship can be obtained: clock frequency Is 4 times the core frequency, and the equivalent frequency is 2 times the clock frequency, that is DDR3 memory The equivalent frequency is 8 times the core frequency. [4]
DDR 3 memory includes the following types: DDR3 1066/1333/1600/1800/2000. The core frequencies are 133 MHz, 166 MHz, 200 MHz, 225 MHz and 250 MHz respectively. The clock frequencies are 533 MHz, 667 MHz, 800 MHz, 900 MHz and 1000 MHz respectively. The equivalent frequencies are 1066 MHz, 1333 MHz, 1600 MHz, 1800 MHz and 2000 MHz respectively. The maximum data transmission bandwidth of a single DDR3 memory is 2000 MHz × 64 bit ÷ 8 - 16 GB/s. [4]
5) DDR4 SDRAM
(Double Data Rate 4 SDRAM ）1.2V working voltage is adopted, memory data bit width is 64 bits, and 16 bit data is pre read. If the dual channel mechanism is canceled, one memory is one channel. working frequency Up to 4266 MHz, single DDR4 Memory data transmission The bandwidth is up to 34 GB/s. [4]

Classification by system logic

1） Expand memory
In 1984, shortly after 286 was widely accepted, people increasingly realized that the 640KB limit had become an obstacle to large programs. At this time, Intel and Lotus, two outstanding representatives of hardware and software, jointly developed a scheme combining hardware and software, which made it possible for all PCs to access more than 640KB of RAM. Microsoft just launched Windows Memory space It also has high requirements, so it joined the ranks in time. [5]
At the beginning of 1985, Lotus, Intel and Microsoft jointly defined LIM-EMS, namely Extended Memory Specification EMS is usually called expanded memory.
At that time, EMS needed a memory expansion card installed in the I/O slot and a memory expansion card called EMS Expand memory Management procedures Can be used. But I/O slot Address line Only 24 bits（ ISA bus ）This is not suitable for 32-bit computers of 386 or above.
Therefore, memory expansion cards are rarely used nowadays. Nowadays, the expanded memory in microcomputer is usually realized by software such as DOS EMM386 in Extended memory Simulate or expand memory for use. Therefore, the difference between expanded memory and extended memory is not in its Physical storage It depends on the method used to read and write it. Further introduction will be given below. [5]
As mentioned earlier, extended memory can also be Analog conversion And become. Principle of EMS and XMS Different, it uses Page frame Mode. A page frame is a 64KB space (usually in the reserved memory area, but its physical memory is from the extended memory) specified in a 1MB space. It is divided into 4 pages, 16KB each. EMS memory is also 16KB paging , 4 pages of content can be exchanged each time, and all EMS memories can be accessed in this way.
There are many EMS compliant drivers, including EMM386.EXE QEMM, TurboEMS, 386MAX, etc. Both DOS and Windows provide EMM386 EXE。 [5]
2) Extended memory
Extended Memory Diagram
As we know, there are 24 people in 286 Address line , which can address 16MB address space 386 has a 32-bit address line, which can address up to 4GB of address space. For the sake of distinction, we call the address space above 1MB as extended memory XMS (eXtend memory). [5]
There are two working modes of memory in computers above 386 level, one is called real address mode or real mode, and the other is called protection mode. In real mode, Physical address 20 bits are still used, so the maximum Addressing space 1MB for compatibility with 8086. 32 bit protection mode Physical address The addressing range can reach 4GB.
The DOS system works in real mode, and the memory space it manages is still 1MB, so it cannot directly use the extended memory. To this end, Lotus, Intel, AST and Microsoft established the standard for the use of extended memory under MS-DOS, namely, the extended memory specification XMS. Himem.sys, which we often see in the Config.sys file, is the driver for managing extended memory. [6]
The appearance of the extended memory management specification is later than that of the extended memory management specification.
3） High end memory area
In real mode, Memory unit The address of can be recorded as:
Segment address : intra segment offset [5]
Memory
Usually used hexadecimal It is written as XXXX: XXXX. Actual Physical address By segment address Shift Left The 4 bits are then added with the intra segment offset. If each address is 1, it is FFFF: FFFF. Its actual Physical address It is: FFF0+FFFF=10FFEF, about 1088KB (16 bytes less), which has exceeded 1MB and entered the extended memory. The area entering the extended memory is about 64KB, the first 64KB of more than 1MB.
We call it High end memory area HMA（High Memory Area）。 The physical memory of HMA is obtained from the extended memory. Therefore, to use HMA, physical extended storage must exist. In addition, the establishment and use of HMA also requires an XMS driver HIMEM. SYS , so only HIMEM is loaded SYS before HMA can be used. [5]
4） Upper memory
To explain the concept of upper memory, we have to go back to the reserved memory area. The reserved memory area refers to the area of 640KB~1024KB (384KB in total). This part of the area was clearly reserved for the system at the beginning of the PC, and the user program could not access it. However, this part of the space is not fully used, so everyone wants to make a decision on the remaining part and divide it address space (Note: address space, not physical memory). Then another memory area UMB is obtained. [5]
UMB (Upper Memory Blocks) is called Upper memory Or upper memory block. It is generated by squeezing the remaining unused space in the reserved memory. Its physical memory is still taken from the physical extended memory. Its management driver is the EMS driver. [5]
5） Shadow memory
For machines with 1MB or more physical memory, how to use the 640KB~1024KB physical memory. Because of this part address space It has been allocated for system use, so it cannot be reused.
In order to use this part of physical memory, some 386 systems provide a relocation function, that is Address relocation 1024KB~1408KB. In this way, this part of physical memory becomes extended memory, which can be used of course.
However, this relocation function is no longer used in today's high-end machines, and this part of physical memory is reserved as Shadow memory. What shadow memory can occupy address space It is the same as the corresponding ROM. Shadow is composed of RAM, which is much faster than ROM.
When the contents of ROM (various BIOS programs) are loaded into the Shadow RAM You can access BIOS from RAM without having to access ROM. This will greatly improve system performance. Therefore, when setting CMOS parameters, The The corresponding Shadow area is set to Enabled. [5]
  • summary
After the above analysis, the division of internal memory can be summarized as follows: [5]
● Basic memory It occupies 0~640KB address space.
Memory
● The reserved memory occupies 640KB~1024KB address space. Assign to Display Buffer memory , each adapter ROM and system ROM BIOS on the Upper memory UMB。 The physical storage of UMB is taken from the physical extended storage. This range of physical RAM can be used as Shadow RAM. [5]
● Upper memory (UMB) Use the unallocated address space The physical memory is obtained from the physical extended memory. UMB is managed by EMS, and its size can be controlled by EMS Driver set up. [5]
● High end memory (HMA) Extended memory The first 64KB area in (1024KB~1088KB). By HIMEM SYS establishment and management. [5]
● XMS memory conforms to the extended memory area managed by XMS specification. his Driver HIMEM SYS。 [5]
● EMS memory conforms to the expanded memory area managed by EMS specification. Its driver is EMM386.EXE, etc. [5]

Other types

  • SRAM
SRAM (Static RAM) means static random access memory. SRAM data does not need to be saved through continuous refreshing, so it is faster than DRAM（ Dynamic random access memory ）Much faster. However, the disadvantages of SRAM are that DRAM requires a lot of transistors and generates a lot of heat compared with its capacity. Therefore, it is difficult for SRAM to become a high-capacity Main memory , usually only used as cache in CPU and GPU, and the capacity is only tens of K to tens of M. [5]
One branch of SRAM is eSRAM (Enhanced SRAM), which is an enhanced SRAM with larger capacity and higher operating speed. [5]
  • RDRAM
RDRAM is the memory launched by RAMBUS. RDRAM Memory module 16bit, but the SDRAM is higher than that of the same period Operating frequency , very strong performance. [5]
However, it is a non open technology, and memory manufacturers need to pay licensing fees to RAMBUS. also RAMBUS memory Another major problem of is that empty channels are not allowed to exist. They must be used in pairs. Idle slots must be used Terminator 。 Therefore, except for the short-lived Intel i820 and i850 chipsets, the PC platform does not support RAMBUS memory chipsets.
It can be said that it is an excellent technology, but not a successful commercial product. [5]
  • XDR RAM
XDR memory It is an upgraded version of RDRAM. It is still launched by RAMBUS. XDR is the abbreviation of "eXtreme Data Rate".
XDR still has the problems that RDRAM cannot be widely used deficiencies 。 Therefore, the application of XDR memory is still very limited. The common ones are Sony Of PS3 game console 。 [5]
  • Fe-RAM
Ferroelectric memory It is a nonvolatile memory that will not lose content when power is cut off high-density 、 low power consumption And radiation resistance. Because the data is iron The magnetism of the element is stored, so, Ferroelectric memory No need to continue refresh data 。 Its running speed will be very optimistic. And it needs fewer transistors than SRAM. It is considered by the industry as the most likely alternative to SDRAM. [5]
  • MRAM
Magnetic memory. It and Fe RAM have Similarity , still based on Magnetic material To record data. [5]
  • OUM
Phase change memory 。
In 1968, Stanford Ovshinsky published his first article on Amorphous The thesis of phase transition, founded amorphous semiconductor science. A year later, he first described Phase transition theory Memory: In the process of material changing from amorphous state to crystalline state, and then back to amorphous state, its amorphous and crystalline state show different reflective characteristics and resistance characteristics, so we can use the amorphous and crystalline state to represent "0" and "1" respectively Store data 。 [5]

Interface type

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Memory interface types include DIP, SIMM and DIMM There are three types (RDRAM adds RMM), of which the last two are what we want to focus on. [7]

DIP

DIP is the abbreviation of "Dual n-Line Package", that is, dual in-line memory chip. Its common single chip capacity is 256 KB , IMB, etc. But now memory is developing so fast, where can it be hundreds of KB and several megabytes of memory? Therefore, the DIP interface has long been an obsolete memory interface. [7]
stay SIMM and DIMM Interface type memory module, multiple RAM The chip is soldered on a small circuit board and installed on the main board or memory expansion board through a special socket, so they can also be regarded as a Memory chip 。 [7]

SIMM

SIMM Is the abbreviation of "Single Line Memory Module", that is, single in-line memory module, which is 5x86 and earlier PC Memory commonly used in Interface mode 。 In earlier PC Medium (before 486), 30 needle SIMM Interface, while Pentium The 72 pin machine is more widely used in the class of machines SIMM Interface, or with DIMM Interface types coexist. The 72 line memory module is slightly larger and provides 32-bit effective data bits. The common capacities are 4MB.8MB, 16MB and 32MB. [7]

DIMM

DIMM It is the abbreviation of "Dual In Line Memory Module", that is, dual in-line memory module, that is, both sides of the memory board with this type of interface have data interface Contact (commonly known as Goldfinger )。 [7]
such Interface mode The memory of is widely used in today's computers. It is usually 84 pins, but because it is two-sided, there are 168 pins in total, which is commonly referred to as the 168 line memory module. The 168 line memory module is large in size and provides 64 bit effective data bits. [7]
DRAM memory is usually 72 lines, SDRAM The memory is usually 168 lines, and EDO RAM The memory has 72 lines and 168 lines. People often call memory by the pipeline number of memory. But it should be noted that not only SDRAM Memory is 168 line, some SIMM Type A memory also has 168 lines. SIMM The working voltage of is 5v, DIMM Its working voltage is 3.3v. [7]

Technical indicators

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Memory Technical indicators Generally including Parity , number of pins, capacity, speed, etc. The number of pins can be classified as memory Interface type , which will not be discussed here. [7]

Parity

Odd/ Even check （ ECC ）Yes data transfer A way to correct data errors, divided into Odd check And even check. [7]
If odd parity is used, an additional bit is added to each byte as Check bit When the number of "1" in the original data sequence is odd, the check bit is "0"; otherwise, the check bit is "1", which can ensure that the transmitted data meets the requirements of odd check. When the receiver receives the data, it will detect the number of "1" in the data according to the requirements of odd parity check. If it is odd, it means the transmission is correct, otherwise it means the transmission is wrong. [7]
Same reason Even check The process of parity check is the same as that of odd check, except that the number of "1" in the detection data is even. [7]

Memory capacity

Memory capacity Same as hard disk floppy disk etc. storage The capacity units are the same Basic unit Both are bytes, and:
Memory
1024B=1KB=1024 bytes=2 ten byte
1024KB=1MB=1048576 bytes=2 twenty byte
1024MB=1GB=1073741824 bytes=2 thirty byte
1024GB=1TB=1099511627776 bytes=2 forty byte
1024TB=1PB=1125899906842624 bytes=2 fifty byte
1024PB=1EB=115 292150 4606846976 bytes=2 sixty byte
1024EB=1ZB=1180591620717411303424 bytes=2 seventy byte
1024ZB=1YB=1208925819614629174706176 bytes=2 eighty byte [7]
Whether the memory module can memory bank ( Bank ）Installing for a unit will determine whether the memory works properly, which is different from the data bus The number of bits is related. The number of bits in the data bus is different for different models of computers.
Memory modules usually have 64MB, 128MB, 256MB and other capacity levels. From this level, we can see that the memory module capacity has doubled. That is, if the memory module capacity is 512MB, it means that it will be 1024MB in the next step. [7]
At present, 8GB and 16GB memory have become mainstream configurations. SDRAM The memory module has two designs, one side and two sides. Each side uses 8 or 9 SDRAM chips (the extra one is ECC test). [7]

Access time

Access time It is another important indicator of memory. Its unit is nanosecond (ns). Common SDRAM includes 6ns, 7ns, 8ns, 10ns, and so on Superscript 6, - 7, - 8, - 10, etc.
The smaller the value, Access speed The faster, the higher the price. When selecting memory, try to select CPU Of Clock cycle This will help maximize the efficiency of memory modules. [7]
Slow memory and fast motherboard will affect CPU speed, and may cause System crash ； The memory is fast while the motherboard is slow, which can only be caused by overqualified students Resource waste 。
When the memory access time is 10ns, its clock frequency Up to 100MHz, which means 100MHz fsb Motherboard use; When the access time is 7ns, the clock frequency can reach 142MHz at most, and the external frequency of the motherboard can reach above 133MHz.
However, many memory modules printed with "- 8", "- 7" or even "- 6" on the market do not meet their nominal targets. [7]

CL delay

Memory
CL reaction time is another indicator of memory balance. CL is CAS Latency Abbreviation of, which refers to the delay time In short, it is the memory that receives instructions from the CPU reaction rate 。
General Parameter value There are 2 and 3. The smaller the number, the shorter the reaction time. In the early PC133 memory standard, this value was specified as 3, while in the new Intel specification, CL's reaction time Must be 2.
To a certain extent, for the assembly of chips and PCBs of memory manufacturers technological requirements Relatively high, but also to ensure a better quality. Therefore, this is a factor that cannot be ignored when purchasing brand memory. [7]
There is another interpretation: Memory latency Basically, it can be interpreted as the time for the system to wait for a memory response before entering the data access order state.
To make a vivid analogy, it is like the process of eating in a restaurant. You need to order first, and then wait for the waiter to serve you.
In the same way, the shorter the memory delay time is set, the faster the computer can read data from the memory, and the higher the other performance of the computer.
This rule applies to both Intel as well as amd processors In the system. Since there is no lower latency than 2-2-2-5, international memory Standards Organization Think that with the current Dynamic memory Technology is not yet able to implement 0 or 1 latency. [7]
Usually, we use four connected Arabic numerals To indicate a memory delay, such as 2-2-2-5. Among them, the first number is the most important. It represents CAS Latency, that is, the delay time required for memory access to data.
The second number represents RAS-CAS delay, and the next two numbers represent RAS respectively Pre charge time And Act to Recharge delay. The fourth number is generally the largest among them. [7]

frequency

Memory frequency test chart
Main frequency of memory And CPU Dominant frequency Similarly, it is used to indicate the speed of memory. It represents the highest memory working frequency 。
Main frequency of memory Yes MHz （ Megahertz ）It is measured in units. Main frequency of memory The higher the memory is, to some extent, the faster it can reach. The main frequency of the memory determines the maximum frequency at which the memory can work normally.
Current mainstream Memory frequency yes DDR4 , and higher memory frequency DDR5 。 [7]
computer system Of Clock speed It is measured by frequency. crystal oscillator Control the clock speed, apply voltage to the quartz chip sine wave The vibration can be realized through the deformation And size.
The vibration of the crystal is shown in the form of sinusoidal harmonic changing current, which is clock signal 。 The memory itself does not have a crystal oscillator, so the clock signal when the memory is working is determined by Mainboard chipset Of North Bridge Or directly from the motherboard Clock generator That is, the memory cannot determine its own operating frequency, but its actual operating frequency is determined by the motherboard. [7]
DDR memory and DDR2 The frequency of memory can be expressed in two ways: operating frequency and equivalent frequency. The operating frequency is Memory granule The actual operating frequency, but because the DDR memory can Falling edge Both transmit data, so the equivalent frequency of the transmitted data is twice the working frequency; Each clock of DDR2 memory can read/write data at a speed four times the working frequency, so the equivalent frequency of data transmission is four times the working frequency.
For example, the working frequencies of DDR 200/266/333/400 are 100/133/166/200MHz respectively, while the equivalent frequencies are 200/266/333/400MHz respectively; DDR2 The operating frequencies of 400/533/667/800 are 100/133/166/200MHz respectively, while the equivalent frequencies are 400/533/667/800MHz respectively. [7]

bandwidth

Functionally, we can think of memory as Memory controller (generally located at North Bridge Chip) and CPU or warehouse. Obviously, the memory capacity determines the size of the "warehouse", while the memory bandwidth determines the width of the "bridge". Both are indispensable. This is what we often call "memory capacity" and“ Memory speed ”。
In addition to memory capacity and memory speed, the delay period is also the key to determine its performance. When the CPU needs the data in memory, it will issue a Memory controller The memory controller then sends the request to the memory and receive data Report to the CPU the time required for the entire cycle (from the CPU to the memory controller, and then back to the CPU). [7]
There is no doubt that shortening the entire cycle is also the key to improving the memory speed, which is just like the police working on the bridge. Its command and unblocking ability is also one of the factors determining the degree of smoothness.
Faster memory technology contributes significantly to overall performance, but improves Memory bandwidth It is only part of the solution, and the data is CPU And inter memory transfer usually takes more time than the processor performing function It takes longer, so buffers are widely used.
In fact, the so-called Buffer It is in the CPU L1 cache And L2 Cache They are the "bridge" between the memory and the CPU.
In fact, L1 cache and L2 cache use SRAM , we can also broadly understand it as“ Memory bandwidth ”, but now it seems more interpreted as“ Front end bus ”, so we just mention it briefly.
Give us a preview“ Front end bus ”And“ Memory bandwidth ”There is a close connection between them, and we will have a deeper understanding in the later tests. [7]
  • Bandwidth Importance
Basically, when the CPU receives instructions, it will first look for relevant data from the L1 Cache in the CPU. Although the L1 Cache runs at the same frequency as the CPU, it cannot hit every time because of its small capacity.
At this time, the CPU will continue to the next level L2 Cache （ L2Cache ）In the same way, when the required data is not available in the L2 cache, it will continue to move to L3Cache (if any, such as K6-2+and K6-3), memory and hard disk. [7]
At present, the system processes a huge amount of data, so almost every step of operation has to go through memory, which is also the most frequently working component in the whole system.
In this way, the performance of the memory determines the performance of the system to a certain extent Multimedia Design It is more obvious in software and 3D games. 3D graphics card Memory bandwidth (perhaps called Video memory It is also self-evident that bandwidth is more appropriate, and its effect is even more obvious than the memory bandwidth of the system.
As you know, Display card In progress Pixel Shader From Video memory Read and write data in different buffers of. Some of these buffers have placement description pixels ARGB（ Alpha channel , red, green, blue), and some pixels Z value (Data used to describe the depth or visibility of pixels).
Obviously, once the Z-axis data is generated, the burden of video memory will rise abruptly Texture mapping , depth complexity rendering 3D special effects 。 [7]
  • Increase memory bandwidth
The calculation method of memory bandwidth is not complicated. You can follow the following Calculation formula : bandwidth=bus width × bus frequency × one Clock cycle Internally interchangeable data packet number.
Obviously, in these multiplier Each of the factors will have a great impact on the final memory bandwidth. However, there is not much to write about the frequency nowadays. After all, it is limited by the manufacturing process and cannot be multiplied in a short time.
The bus width and the number of data packets are quite different. A simple change will Memory bandwidth make a spurt of progress. DDR technology makes us feel the benefits of increasing the number of data packets. It makes Memory bandwidth Crazily doubled.
Of course, the method to increase the number of data packets is not only limited to writing on the memory, but also can work through multiple memory controllers in parallel, which is now the popular dual channel DDR Chipset (e.g. nForce2, I875/865, etc.). [7]
in fact, Dual channel DDR Memory controller It is not a new invention, because as early as the RAMBUS era, RDRAM Similar technologies have been used, but at that time, the bus width of RDRAM was only 16Bit, which could not be compared with the 64Bit of DDR.
Memory technological development At this stage, the emergence of the four channel memory controller is only Time issues ， VIA Of QBM Technology and SiS chipset supporting four channel RDRAM are the future development directions.
As for video cards Video memory bandwidth More sensitive, which is even an important aspect used by many manufacturers to distinguish between high and low end products. Also use DDR video memory 128Bit wide products will be far better than 64Bit wide products.
Of course, improve Memory frequency It is also a solution, but its effect is not obvious, and it will greatly increase the cost. It is worth noting that some high-end graphics cards have even used DDRII Technology, but at least for now, this technology is too early. [7]
  • Identify memory bandwidth
For memory, it is quite simple to identify memory bandwidth, because SDRAM 、 DDR RDRAM and RDRAM are very different in appearance Secondary drawing Can be clearly recognized.
The only thing we need to identify is DDR memory with different frequencies. At present, the mainstream DDR memory is divided into DDR266 、 DDR333 as well as DDR400 , of which the last three digits represent the operating frequency. [7]
adopt Memory module The logo on the can be easily identified. Relatively speaking, it is difficult to identify the video memory bandwidth on the video card. Here, we should focus on "video memory" Bit width ”And“ Memory frequency ”Two important technical indicators.
The calculation method of video memory bit width is: single block Phanerophore Bit width × total number of video memory particles, and video memory frequency is determined by "1000/nanosecond number of video memory particles".
Generally speaking, we can see its nanosecond number from the last two digits of a serial number on the video memory particles, from which we can also know its video memory frequency.
As for the grain bit width of a single video memory, we can only check it online. HY 、 Samsung EtronTech, EtronTech, etc. all provide a dedicated video storage number query website, which is quite convenient. as Samsung The video memory of can be downloaded to the following address, as long as the corresponding video memory particle number is input.
In addition, RivaTuner can also detect the total amount of video memory on the video card Bit width You can see it in the MAIN menu by opening RivaTuner. [7]

Purchasing method

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The workmanship should be excellent

For memory selection, the most important thing is stability and performance, and the level of memory workmanship will directly affect the performance, stability and overclocking.
Memory granule The quality of memory directly affects the performance of memory, which can be said to be the most important core component of memory. So when you buy, try to choose the memory particles produced by large factories.
Common memory granule manufacturers include Samsung , Modern Magnesia , South Asia, silicocene, etc. All of them have gone through complete production processes, so their quality is more guaranteed. And those who use these top memory granules Memory module The quality and performance must be much higher than those of other low-quality memory granules. [7]
Memory PCB Circuit board The function of is to connect Memory chip Pin and mainboard The signal line Therefore, its workmanship is directly related to system stability 。
At present, the number of layers of mainstream memory PCB circuit boards is generally 6, and such circuit boards have good Electrical performance , can effectively shield signal interference. More excellent high specification memories are often equipped with 8-layer PCB circuit boards to achieve better performance. [7]

SPD Hidden Information

SPD Information can be said to be very important, which can directly reflect the performance and system of memory. It stores the indicator information that the memory can work stably, as well as the product production, manufacturer and other information.
However, since each manufacturer can modify the SPD at will, many miscellaneous memory manufacturers will modify the SPD parameters or directly COPY Famous brand products SPD, but once the computer software detection will reveal its true colors. [7]
Therefore, after you buy the memory, you can use the common Everest , CPU-Z and other software. However, it should be noted that the SPD parameters are very important for large brands of memory, but the SPD information is not worth fully believing for low-quality memory. [7]

Counterfeit repaired products

At present, some memory grains of different brands and models are often used. You can see the difference at a glance. At the same time, some pervasive JS will also use the falsification method of polishing memory particles, and then print new numbering parameters. However, after careful observation, it will be found that the polished chip is relatively dull Fuzzing And the words on the overprint are vague and unclear. These are generally counterfeit memory products, which should be noted. [7]
In addition, we should also observe whether the PCB is clean, whether there are burrs, etc, Goldfinger Whether there are obvious traces left by plugging and unplugging. If there are, it is likely that the memory products are repaired (of course, it is not ruled out that some manufacturers have been tested before leaving the factory, but there are a few).
It should be reminded that no matter how cheap the repaired and counterfeit memory is, it is not worth buying because of its serious security risks. [7]

Troubleshooting

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1. No display after startup
because Memory module Cause This type of failure is usually caused by the memory module and the motherboard Memory socket poor contact Cause, just use eraser Rub it back and forth Goldfinger The problem can be solved at the location (do not use alcohol to clean). In addition, memory damage or a problem with the motherboard memory slot can also cause such failures. [1]
Memory [1]
because Memory module There is no display fault when starting the machine speaker It usually beeps for a long time (for Award Bios)
2、 windows The system is unstable and often produces illegal errors
This kind of failure is generally caused by Memory chip It is caused by poor quality or software, if it is determined that it is Memory module The reason is that there is only one way to change. [1]
3、windows registry Frequently damaged without reason, prompting the user to recover
Such failures are generally caused by Memory module It is caused by poor quality and is difficult to repair, so it can only be replaced. [1]
4. Windows often enters automatically safe mode
This kind of fault is generally caused by the main board and Memory module Incompatibility or poor quality of memory modules. Usually, PC133 memory is used on some motherboards that do not support PC133 memory modules. You can try CMOS Reduce the memory reading speed within the setting to see whether the problem can be solved. If not, the only way is to replace the memory module. [1]
5. Randomness crash
This kind of fault is generally due to the use of several different chips Memory module , because the speed of each memory module is different, there is a time difference crash This can be solved by reducing the memory speed in the CMOS settings. Otherwise, only the memory of the same model can be used. Another possibility is Memory module Incompatibility with the motherboard, which is generally rare. In addition, the computer randomness may be caused by poor contact between the memory module and the motherboard crash This kind of phenomenon is quite common. [1]
6. After increasing the memory system resource Instead, it decreases
This phenomenon is generally caused by the incompatibility between the motherboard and the memory, which is common in PC133 Memory module It is used on some motherboards that do not support PC133 memory modules, even if System reassembly It can't solve the problem. [1]
7. When Windows starts, the system prompts that there is a problem with some addresses when loading the high-end memory file himem.sys
This problem is usually caused by Memory module Some chips of, resolvent See the memory maintenance method below. [1]
8. Often occurs when running some software insufficient memory Tips for
This phenomenon is generally due to System disk The surplus space is insufficient, so you can delete some useless files and leave more space, which is generally about 300M. [1]
9. When you boot from the hard disk to install Windows and check the disk space, the system prompts that the memory is insufficient
This kind of fault is generally caused by the user config.sys The emm386.exe file is added to the file. You can solve the problem by masking it. [1]
10. Install windows to system configuration An illegal error occurred when
This kind of failure is generally caused by the damage of the memory module, which can be solved by the memory maintenance method. If not, the only way is to replace the memory module. [1]
11. The system automatically restarts several times when starting Windows
Such failures are generally caused by Memory module Or there is a problem with the power quality. Of course, the system restart may also be caused by poor CPU cooling or other man-made faults. This is only useful Exclusion method Step by step exclusion. [1]
12. Memory maintenance method
After the above faults occur, if the memory is damaged or the chip quality is poor, it can be used if conditions do not permit Soldering iron Remove the chips on one side of the memory to see whether the problem can be solved. If not, replace and remove the chips on the other side until it is successful (so that the welder is afraid of the person who needs to repair the phone).
Of course, conditional Oscilloscope Testing will get twice the result with half the effort.) After using this method, only half of the memory is available because one chip of the memory has been removed. For example, there is still 32M available for 64M memory. Therefore, there is no need to repair small memory. [1]

Common misunderstandings

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Internal and external memory

This situation mainly occurs in the description Mobile Devices The internal integrated data storage space of. For example, a mobile phone has 512G data storage space Many people describe it as "512G memory". In fact, this statement is wrong, because the so-called "512G memory" is a External memory 。 "Internal external memory" cannot be called "memory" for short, because memory is a specific concept, which is called "internal memory" for short. [1]

Memory card capacity

Memory card The capacity of should not be called "memory" for short, because it is also external memory. [1]
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