Digital-electronics 简明教程
Memory Devices
内存是计算机或任何其他数字系统的重要部分之一。它用于保存处理和执行任务所需的数据和程序。
Memory is one of the important parts in a computer or any other digital system. It is used to hold data and programs required for processing and performing tasks.
内存还会影响数字系统的性能、效率和速度。如今，半导体内存很流行，因为它们提供了非常高速的操作、大的存储容量和紧凑的尺寸。
Memory also affects the performance, efficiency, and speed of the digital system. These days, semiconductor memories are popular, as they provide a very high-speed operation, large storage capacity, and compact size.
在这里，我们将解释与半导体存储器件相关的从基本到高级的概念。
Here, we will explain the basic to advanced concepts related to semiconductor memory devices.
What is Memory?
在数字电子领域，存储器是一种用于存储计算机和其他基于微处理器的系统中数据和指令的设备。在现代数字系统中，存储器由半导体材料制成，并被称为 semiconductor memory 。
In the field of digital electronics, the memory is a device that is used to store data and instruction in the digital systems like computers and other microprocessor-based systems. In modern digital systems, the memory is made up of semiconductor materials and known as semiconductor memory.
存储器是计算机或任何其他数字系统中提供存储空间的设备，其中要处理的数据和处理所需指令被存储。
The memory is the device that provides the storage space in computer or any other digital system where data is to be processed and instructions required for processing are stored.
存储器被划分为大量的小部分。每个部分称为存储器单元。每个存储器单元或位置都有一个唯一分配的地址，该地址从 0 到总存储器大小减一。
The memory is divided into a large number of small parts. Each part is called a memory cell. Each memory cell or location has a unique address assigned to it which varies from zero to total memory size minus one.
例如，如果一台计算机具有 64 kB 的存储器大小，则该存储器单元具有 64 × 1024 = 65536 个存储器位置或单元。因此，这些位置的地址范围从 0 到 65535。
For example, if a computer has 64 kB memory size, then this memory unit has 64 × 1024 = 65536 memory location or cells. Hence, the address of these locations ranges from 0 to 65535.
Classification of Memory
存储器主要分为两种类型，它们是：内部存储器和外部存储器。
Memory is primarily classified into two types, they are: Internal Memory and External Memory.
Internal Memory
内部存储器也称为 primary memory ，因为它直接连接到数字系统的硬件架构。它通常以 IC 的形式安装在系统的主板上。
Internal memory is also known as primary memory, as it is directed connected to the hardware architecture of the digital system. It is typically installed in the system’s motherboard in form of ICs.
内部存储器的示例包括高速缓存存储器、RAM（随机存取存储器）、ROM（只读存储器）等。
Examples of internal memory include cache memory, RAM (Random Access Memory), ROM (Read Only Memory), etc.
External Memory
外部存储器也称为 secondary memory 。此存储器不直接连接到系统的硬件架构，而是通过电缆作为外围设备进行连接。
External memory is also known as secondary memory. This memory is not directly connected to the hardware architecture of the systems, instead it is connected through cables as a peripheral device.
外部存储主要用于提供其他存储空间以永久存储数据和指示。外部存储的示例有 CD、DVD、硬盘驱动器、固态硬盘、USB 驱动器等。
The external memory is primarily used to provide additional storage space to store data and instructions permanently. Examples of external memory are CD, DVD, HDD, SSD, USB drives, etc.
Memory Hierarchy
内存层级结构定义为基于其特征（主要是速度和容量）在数字系统中使用的不同类型内存设备的布置。内存层级结构有助于我们在特定级别为系统选择合适的内存进行使用。
Memory hierarchy is defined as an arrangement of different types of memory devices used in a digital system depending on their characteristics, primarily speed and capacity. The memory hierarchy helps us to select an appropriate memory to use in our system at a specific level.
不同内存设备的典型内存层级结构如下图所示：
A typical memory hierarchy of memory for different memory devices is shown in the following figure −
当我们从上至下查看时，此内存层级结构的一些关键特征包括：
Some of key characteristics of this memory hierarchy, when we go from top to bottom −
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Capacity in terms of storage increases.
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Cost per bit of storage decreases.
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Frequency of access of the memory by the CPU decreases.
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Access time by the CPU increases.
Functional Block Diagram of Memory
内存基本上是多存储单元的集合，具有执行数据读/写操作的支持电路。下图描述了典型内存设备的功能框图：
A memory is basically a group of multiple storage cells having a support circuit to perform data read/write operations. The following figure depicts the functional block diagram of a typical memory device −
它包含以下主要部件：
It consists of the following main parts −
Address Lines
这些线用于加载特定内存位置或单元的地址。
These lines are used to load the address of a specific memory location or cell.
Data Lines
这些线用于从/向内存单元读写数据。
These lines are used to read and write the data from/to the memory cell.
Read and Write Signal (R/W’)
该信号用于从/向内存单元读写数据。当 R 信号变高时，选定单元的数据被加载到数据线上。当 W' 线变低时，数据线上数据被加载到选定的内存单元中。
This signal is used to read and write the data from and to the memory cells. When the R signal is high, the data of the selected cell gets loaded on the data line. When the W’ line goes low, the data on the data line is loaded into the selected memory cell.
Chip Select Signal (CS’)
该信号用于启用或禁用内存芯片。它是一个低电平有效信号，这意味着当该信号变低时，内存芯片被启用并允许读写操作执行。否则，内存芯片将被禁用。
This signal is used to enable or disable the memory chip. It is an active low signal, which means when this signal goes low, the memory chip is enabled and allow the read and write operations to execute. Otherwise, the memory chip will be disabled.
Important Terms Related to Memory Operation
以下是一些与内存读写操作相关的重要术语和定义：
The following are some important terms and definitions which are related to the read and write operations of memory −
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Write Cycle Time − The write cycle time is defined as the minimum amount of time for which a valid cell address is available for data writing operation in the cell. Typically, it is of the order of 200 ns.
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Write Pulse Time − The minimum duration of a write pulse is termed as write pulse time and it is of the order of 120 ns.
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Write Release Time − The minimum time for which the memory address is valid before the write pulse is known as write release time.
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Data Setup Time − The minimum amount of time for which the data remains valid before the write pulse ends is known as data setup time. Typically, it is around 120 ns.
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Data Hold Time − The minimum amount of time for which the data remains valid after the write pulse ends is known as data hold time.
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Read Cycle Time − The minimum amount of time for which a valid memory address remains available for reading the data from a memory cell is known as read cycle time. It is typically of the order of 200 ns.
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Access Time − The amount of time required to access data from a memory cell is referred to as access time of the memory. It is also of the order of 200 ns.
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Read to Output Active Time − The minimum time that required for enabling the output buffer after starting of the read pulse is called the read to output active time. Typically, this time is of the order of 20 ns.
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Read to Output Valid Time − The maximum delay time between the beginning of the read pulse and the availability of the valid data at the data output line is known as "read to output valid time".
这是了解存储器件的读写操作所需的几个关键术语。
These are some key terms whose knowledge is required to understand the read and write operations of a memory device.
Characteristics of Memory Devices
在本节中，我们将重点研究存储器件的一些关键特征及其定义和重要性−
In this section, we will focus on studying some key characteristics of memory devices and their definitions and importance −
Storage Capacity
此参数表示设备的总存储器。通常以它可以存储的字节数来表示。例如，1k × 8 位的存储器可以存储 1024 × 8 = 8192 字节的数字数据。
This parameter denotes the total memory of the device. It is generally expressed in terms of number of Bytes that it can store. For example, a memory of 1k × 8 bits can store 1024 × 8 = 8192 Bytes of digital data.
Unit of Data Transfer
在一次读或写周期中可读写位数称为数据传输单位。通常，数据传输单位等于处理器的字长或数据总线大小。
The number of bits that can be read or written in a single read or write cycle is called the unit of data transfer. In general, the unit of data transfer is equal to the word length or size of the data bus of the processor.
Modes of Access
它指的是可以读取或写入存储器中的数据的方式。数字存储器件中使用了以下三种模式−
It refers to the way in which the data can be read or write to the memory. There are following three modes used in digital memory devices −
在此模式中，数据以预定义的顺序方式读出或写入存储器。换句话说，要访问第二个文件，我们首先访问第一个文件，要访问第三个文件，首先访问第一个和第二个文件，依此类推。
In this mode, the data is read from or write to the memory in a predefined sequential manner. In other words, to access the second file, we first access the first file, to access the third file, firstly access the first and second files, and so on.
在此模式中，我们可以直接访问任何顺序的任何存储器位置。
In this mode, we can directly access any memory location in any order.
此模式是顺序访问模式和随机访问模式的组合。它也被称为半随机访问模式。
This mode is a combination of sequential and random access modes. It is also termed as semi-random access mode.
Types of Memory Devices
这里列出了和解释了计算机和数字系统中使用的一些重要的存储器设备分类。
Some of the important classifications of memory devices used in computers and digital systems are listed and explained here.
基于数据存储性质的存储器分类−
Classification of memory on the basis of nature of data storage −
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Volatile Memory
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Non-Volatile Memory
基于访问模式的存储器分类−
Classification of memory on the basis of access modes −
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Sequential Access Memory
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Random Access Memory
现在，让我们详细讨论所有这些类型的存储器及其子类型和特征。
Now, let us discus all these types of memories in detail along with their subtypes and characteristics.
Volatile Memory
一种需要持续供电来维护所存储数据的存储器类型称为 volatile memory 。如果断开存储器的电源，存储在其中的数据将会丢失。因此，它也被称为 temporary memory 。
A type of memory that requires continuous power supply to maintain the stored data is called a volatile memory. If the power supply to the memory is turned off, the data stored in it will be lost. Therefore, it is also termed as temporary memory.
断电时，易失性存储器会丢失其存储的数据。易失性存储器的操作速度快，因此它可以在短时间内读写数据。
The volatile memory loses its stored data when power supply to it is turned off. Volatile memory has fast operational speed; thus, it can read and write data in a short span of time.
易失性存储器用于存储需要访问的数据并执行操作。RAM（随机访问存储器）是易失性存储器的示例。
Volatile memory is used to store data required to be accessed and perform operations. RAM (Random Access Memory) is an example of volatile memory.
Non-Volatile Memory
即使没有供电也可以保留存储数据的存储器类型称为 non-volatile memory 。它也称为永久存储器，用于长期存储数字数据。
A type of memory which can retain stored data even when no power supply is present is known as non-volatile memory. It is also known as permanent memory and is used for long-term storage of digital data.
非易失性存储器永久存储数据。即使断电，它也可以保留存储的数据。
Non-volatile memory stores data permanently. It can retain the stored data even when the power supply is switched off.
非易失性内存比易失性内存慢。因此，该内存有更长的读取和写入周期。
Non-volatile memory is slower than volatile memory. Hence, this memory has longer read and write cycles.
非易失性内存的示例包括 ROM（只读存储器）、磁带、光盘、磁碟、USB 驱动器等。
Examples of non-volatile memory includes ROM (Read Only Memory), magnetic tapes, optical discs, magnetic discs, USB drives, etc.
Sequential Access Memory
一种按预定义的顺序方式访问存储的数据和信息内存类型被称为 sequential access memory 。
A type of memory in which the stored data and information is accessed in a predefined sequential manner is known as a sequential access memory.
有时，它也称为 serial access memory ，因为按序列化方式检索存储的数据。
Sometimes, it is also known as serial access memory, as the stored data is retrieved in a serial order.
在顺序访问内存中，系统必须从内存地址的开头开始搜索存储设备，直到找到所需的数据片段。换句话说，为检索所需数据，系统必须访问所有内存地址，直到访问到所需数据。
In a sequential access memory, the system must search the storage device from the beginning of the memory address until it finds the required piece of data. In other words, to retrieve the desired data, the system must access all memory addresses until it reaches the desired data.
在顺序访问内存中，数据检索流程以顺序方式执行。其中，系统从内存开头开始，并顺序地遍历所有内存地址，直到获得所需数据。
In a sequential access memory, data retrieval process executes in a sequential manner. Where, the system starts from beginning of the memory and go sequential through all memory addresses until the desired data is obtained.
顺序访问内存的访问速度较慢，且读/写时间较长。磁带是顺序访问内存的示例。
Sequential access memory has slower access speed and longer read/write time. Magnetic tapes are the examples of sequential access memory.
Random Access Memory
随机访问存储器，也称为直接访问存储器，是一种可以不经由前置数据而直接访问所需数据的内存类型。因此，该内存允许按任意顺序访问任何数据。
Random access memory, also called as direct access memory, is a type of memory in which the desired data can be accessed directly, without going through the preceding data. Hence, this memory allows to access any data in any order.
换句话说，直接访问存储器或随机访问存储器能够在同一时间对内存中的任意存储位置数据进行读取或写入。因此，所有存储单元的访问时间都是相同的，且不取决于存储器阵列内单元的物理位置。
In other words, the direct access memory or random access memory has the ability to read from or write to data in any memory location in the same time. Hence, the access time for all the memory cells is the same and it does not depend on the physical location of the cell within the memory array.
随机访问存储器允许按任意随机顺序访问数据。它提供高速数据访问，即快速读写操作。
Random access memory allows data to be accessed in any random order. It provides high speed data access i.e., fast read and write operations.
随机访问存储器的所有存储位置都可直接访问数字系统的处理元件。
All memory locations of the random access memory are directly accessible to the processing element of the digital system.
随机访问存储器的示例包括 RAM、ROM、硬盘、光盘和其它半导体存储器等。
Examples of random access memory include RAM, ROM, hard disk, optical disks, and other semiconductor memories, etc.
Conclusion
总之，存储设备是数字系统（如计算机）中存储数据和信息的重要组件。
In conclusion, a memory device is an important component in a digital system like computer used to store data and information.
用于不同目的的不同类型的存储设备。例如，易失性内存（如 RAM）用于保存程序完成前所需的临时数据。
Different types of memory devices are used for different purposes. For example, a volatile memory like RAM is used to hold temporary data which are required till the process is complete.
另一方面，非易失性内存用于更长时间地永久保存数据。例如，硬盘用于在计算机系统中存储用户数据。
On the other hand, a non-volatile memory is used to hold data permanently for a longer period of time. For example, a hard disc is used to store user’s data in the computer system.