计算机组织与体系结构

A memory unit is the collection of storage units or devices together. The memory unit stores the binary information in the form of bits. Generally, memory/storage is classified into 2 categories:

存储单元是一起存储单元或设备的集合。 存储单元以位的形式存储二进制信息。 通常，内存/存储分为两类：

• Volatile Memory: This loses its data, when power is switched off.

  易失性存储器 ：关闭电源后，它将丢失其数据。

• Non-Volatile Memory: This is a permanent storage and does not lose any data when power is switched off.

  非易失性内存 ：这是一个永久性存储，在关闭电源时不会丢失任何数据。

记忆层级 (Memory Hierarchy)

The total memory capacity of a computer can be visualized by hierarchy of components. The memory hierarchy system consists of all storage devices contained in a computer system from the slow Auxiliary Memory to fast Main Memory and to smaller Cache memory.

计算机的总存储容量可以通过组件的层次结构可视化。 内存分层系统由计算机系统中包含的所有存储设备组成，从慢速辅助内存到快速主内存再到较小的高速缓存。

Auxillary memory access time is generally 1000 times that of the main memory, hence it is at the bottom of the hierarchy.

辅助存储器的访问时间通常是主存储器的1000倍 ，因此它位于层次结构的底部。

The main memory occupies the central position because it is equipped to communicate directly with the CPU and with auxiliary memory devices through Input/output processor (I/O).

主存储器占据中心位置，因为它可以通过输入/输出处理器(I / O)直接与CPU和辅助存储设备进行通信。

When the program not residing in main memory is needed by the CPU, they are brought in from auxiliary memory. Programs not currently needed in main memory are transferred into auxiliary memory to provide space in main memory for other programs that are currently in use.

当CPU需要不驻留在主存储器中的程序时，会将它们从辅助存储器中引入。 主存储器中当前不需要的程序被转移到辅助存储器中，以在主存储器中为当前正在使用的其他程序提供空间。

The cache memory is used to store program data which is currently being executed in the CPU. Approximate access time ratio between cache memory and main memory is about 1 to 7~10

高速缓冲存储器用于存储CPU中当前正在执行的程序数据。 高速缓存和主存储器之间的近似访问时间比率约为1到7〜10

内存访问方法 (Memory Access Methods)

Each memory type, is a collection of numerous memory locations. To access data from any memory, first it must be located and then the data is read from the memory location. Following are the methods to access information from memory locations:

每种内存类型都是许多内存位置的集合。 要从任何内存访问数据，首先必须找到它，然后再从内存位置读取数据。 以下是从内存位置访问信息的方法：

1. Random Access: Main memories are random access memories, in which each memory location has a unique address. Using this unique address any memory location can be reached in the same amount of time in any order.

   随机存取 ：主存储器是随机存取存储器，其中每个存储器位置都有一个唯一的地址。 使用此唯一地址，可以在相同的时间内以任何顺序访问任何存储位置。

2. Sequential Access: This methods allows memory access in a sequence or in order.

   顺序访问 ：此方法允许按顺序或顺序访问内存。

3. Direct Access: In this mode, information is stored in tracks, with each track having a separate read/write head.

   直接访问 ：在这种模式下，信息存储在磁道中，每个磁道都有一个单独的读/写头。

主记忆体 (Main Memory)

The memory unit that communicates directly within the CPU, Auxillary memory and Cache memory, is called main memory. It is the central storage unit of the computer system. It is a large and fast memory used to store data during computer operations. Main memory is made up of RAM and ROM, with RAM integrated circuit chips holing the major share.

直接在CPU内部通信的存储单元，辅助存储器和高速缓存存储器称为主存储器。 它是计算机系统的中央存储单元。 它是一种大型且快速的内存，用于在计算机运行期间存储数据。 主存储器由RAM和ROM组成 ，RAM集成电路芯片占据了主要份额。

• RAM: Random Access Memory

  RAM：随机存取存储器

  • DRAM: Dynamic RAM, is made of capacitors and transistors, and must be refreshed every 10~100 ms. It is slower and cheaper than SRAM.DRAM ：动态RAM，由电容器和晶体管组成，必须每10到100毫秒刷新一次。 它比SRAM慢且便宜。
  • SRAM: Static RAM, has a six transistor circuit in each cell and retains data, until powered off.SRAM ：静态RAM，每个单元中都有六个晶体管电路，并保留数据，直到断电为止。
  • NVRAM: Non-Volatile RAM, retains its data, even when turned off. Example: Flash memory.NVRAM ：非易失性RAM，即使关闭，也会保留其数据。 示例：闪存。

• ROM: Read Only Memory, is non-volatile and is more like a permanent storage for information. It also stores the bootstrap loader program, to load and start the operating system when computer is turned on. PROM(Programmable ROM), EPROM(Erasable PROM) and EEPROM(Electrically Erasable PROM) are some commonly used ROMs.

  ROM：只读存储器，是非易失性的，更像是信息的永久存储。 它还存储引导加载程序，以在计算机打开时加载并启动操作系统。 PROM (可编程ROM)， EPROM (可擦除PROM)和EEPROM (电可擦除PROM)是一些常用的ROM。

辅助记忆 (Auxiliary Memory)

Devices that provide backup storage are called auxiliary memory. For example: Magnetic disks and tapes are commonly used auxiliary devices. Other devices used as auxiliary memory are magnetic drums, magnetic bubble memory and optical disks.

提供备份存储的设备称为辅助内存。 例如：磁盘和磁带是常用的辅助设备。 用作辅助存储器的其他设备是磁鼓，磁泡存储器和光盘。

It is not directly accessible to the CPU, and is accessed using the Input/Output channels.

它不能直接由CPU访问，而可以通过输入/输出通道进行访问。

高速缓存存储器 (Cache Memory)

The data or contents of the main memory that are used again and again by CPU, are stored in the cache memory so that we can easily access that data in shorter time.

CPU一次又一次使用的主存储器的数据或内容存储在高速缓存中，以便我们可以在较短的时间内轻松访问该数据。

Whenever the CPU needs to access memory, it first checks the cache memory. If the data is not found in cache memory then the CPU moves onto the main memory. It also transfers block of recent data into the cache and keeps on deleting the old data in cache to accomodate the new one.

每当CPU需要访问内存时，它都会首先检查高速缓存。 如果在高速缓存中找不到数据，则CPU移至主存储器。 它还将最新数据块传输到缓存中，并继续删除缓存中的旧数据以适应新数据。

命中率 (Hit Ratio)

The performance of cache memory is measured in terms of a quantity called hit ratio. When the CPU refers to memory and finds the word in cache it is said to produce a hit. If the word is not found in cache, it is in main memory then it counts as a miss.

高速缓存的性能是根据称为命中率的数量来衡量的。 当CPU引用内存并在高速缓存中找到单词时，据说会导致命中 。 如果在高速缓存中未找到该单词，则该单词位于主内存中，则视为未命中 。

The ratio of the number of hits to the total CPU references to memory is called hit ratio.

命中次数与CPU对内存的总引用数之比称为命中率。

Hit Ratio = Hit/(Hit + Miss)

Hit Ratio = Hit/(Hit + Miss)

联想记忆 (Associative Memory)

It is also known as content addressable memory (CAM). It is a memory chip in which each bit position can be compared. In this the content is compared in each bit cell which allows very fast table lookup. Since the entire chip can be compared, contents are randomly stored without considering addressing scheme. These chips have less storage capacity than regular memory chips.

它也被称为内容可寻址存储器(CAM) 。 它是一个可以比较每个位位置的存储芯片。 在此，在每个位单元中对内容进行比较，从而可以非常快速地进行表查找。 由于可以比较整个芯片，因此可以在不考虑寻址方案的情况下随机存储内容。 这些芯片的存储容量比常规存储芯片要小。

翻译自: https://www.studytonight.com/computer-architecture/memory-organization

计算机组织与体系结构