Memory summary, function and working principle

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什么是内存

•内存是用于存储程序和各类数据信息的核心组件，主要负责数据的存储和读取。根据其功能和用途，内存可分为两类：一类是主内存，通常称为主内存或内存，主要用于临时存储正在运行的程序和数据;另一种是辅助存储器，通常称为辅助存储器或外部存储器，用于长期存储大量的程序和数据信息。

记忆的作用

•计算机的内部存储器是指用于存储数据和指令的半导体存储设备。它主要包括两种类型：只读存储器（ROM，Read Only Memory）和随机存取存储器（RAM，Random Access Memory）。其中，RAM 可以进一步细分为静态随机存储器（SRAM，Static RAM）和动态随机存储器（DRAM，Dynamic RAM）。SRAM 由于其高速特性而经常用于缓存;DRAM 广泛用于形成计算机的记忆棒。另一方面，ROM 主要用于存储固件，例如在 BIOS 芯片中的启动程序。

内存分类

•只读存储器 ROM ： 只读存储器 （ROM） 是计算机制造商通过专用技术固化到芯片上的一种存储介质。它的特点是数据一旦写入，就只能被读取，不能随意修改。ROM 系列包括多种类型，例如掩码 ROM、可编程 ROM （PROM）、可擦除可编程 ROM （EPROM）、电可擦除可编程 ROM （EEPROM） 和闪存 （FLASH）。这种类型的内存通常用于存储不需要频繁更改的程序代码，例如基本输入和输出系统 （BIOS）。ROM 的一个显著优点是它存储的信息是非易失性的，即使在停电的情况下也可以永久保存数据。

•随机内存 RAM：随机存取存储器 （RAM） 是一种用于临时存储程序和数据的易失性存储设备。当电源关闭或关闭电源时，存储在其中的信息会消失。根据其制造技术的差异，现代 RAM 主要采用金属氧化物半导体 （MOS） 技术构建，可分为静态随机存取存储器 （SRAM） 和动态随机存取存储器 （DRAM） 两大类。

记忆棒的类型

•FPM DRAM：快速页面模式动态内存。

•EDO DRAM：扩展数据输出动态内存

•SDRAM：同步动态存储器

•RDRAM: Rambus DRAM high frequency dynamic memory

•DDR SDRAM: Double-rate synchronous dynamic random memory

•DDR II: Memory technology has achieved a significant breakthrough in performance, with its operating frequency being four times higher than traditional SDRAM memory, and has achieved twice the performance improvement compared to the previous generation of DDR memory.

Main parameters of memory stick

•Memory capacity: refers to the total amount of binary data that a single memory stick can store, usually in megabytes (MB) as the unit of measurement.

•Operating frequency: The operating frequency of memory refers to the rate at which the memory module transmits data within a unit of time, usually in megahertz (MHz) as the unit of measurement.

•Data bandwidth: Data bandwidth represents the ability of memory modules to transmit data within a unit of time, and is specifically reflected in the amount of data that can be processed by a single memory operation. As a key indicator for evaluating memory performance, its values directly reflect the data throughput efficiency of memory.

•Parity is the earliest widely adopted memory soft error detection scheme, and data errors are identified through simple parity verification. ECC verification (Error Checking and Correcting) is a more advanced error handling technology, which not only detects data errors, but also has the ability to automatically correct single-bit errors.

•CAS Latency: refers to the time interval required by the memory module to respond to the column address gate signal, which is usually quantized by the CL (CAS Latency) value. This parameter specifically reflects the number of clock cycles between the memory controller sending a column address gate signal to the actual start of data transmission, and is one of the important timing parameters to measure the memory access speed.

•Operating voltage: It is a key electrical parameter to ensure stable memory operation. Memory products from different generations have specific voltage specification requirements. Specifically, the standard operating voltage of SDRAM is 3.3V, the operating voltage of DDR1 memory drops to 2.5V, and the DDR2 memory drops to 1.8V. These voltage values are strictly designed standard parameters and must be strictly followed when used. Any voltage beyond the specified range may cause permanent damage to the memory module.

•SPD (Serial Presence Detect, serial presence detection): is an 8-pin 256-byte EEPROM (electrically erasable programmable read-only memory) chip integrated on the memory module. The chip stores key technical parameters of the memory module, including but not limited to detailed information such as operating frequency, storage capacity, operating voltage, row and column address configuration, and bandwidth. These preset parameters provide the necessary data support for automatic memory configuration at system startup.

Memory encapsulation

•DIP

•SOP

•TSOP

•BGA

•Tiny-BGA

•mBGA

•CSP

Memory interface method

•SIMM 30 line

•SIMM 72 line

•SIMM 168line

•DIMM 184 line

•DIMM 240 line

•RIMM 184 line

Application scope of memory

•The application range of memory is extremely wide, and it penetrates almost all fields that require high-speed data processing and storage, such as automotive electronics, medical equipment, aerospace, etc. Almost all systems and equipment that rely on computer technology cannot do without the core component of memory.

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