20145321 "Information Security system Design Fundamentals" 7th Week Study Summary

20145321 "The basis of information security system Design" 7th Week study summary textbook study content summary sixth chapter

A memory system is a hierarchical structure of storage devices with different capacities, costs, and access times.

6.1 Storage Technology

Three common storage technologies: ram/rom/disk

(1) Random access memory RAM

• There are two categories: Static RAM (SRAM) and dynamic RAM (DRAM) static RAM (SRAM) faster than dynamic RAM (DRAM), but also much more expensive.

• Static RAM

  特点：由于SRAM的双稳态特性，只要有电，它就会永远地保持它的值，即使有干扰，如电子噪音，来扰乱电压，当干扰消除，电路也能恢复到稳定值。应用：SRAM用来作为高速缓存存储器，即可以在CPU芯片上，也可以在片下。

• Dynamic DRAM

 特点：对干扰特别敏感，当电容的电压被扰乱之后，它就永远不会恢复了。暴露在光线下会导致电容电压改变。 应用：DRAM用来作为主存以及图形系统的帧缓冲区。

(2) Non-volatile memory ROM

• Rom has prom,eprom,e2prom,flash;

• ROM distinction: The number of times that can be reprogrammed and the mechanism used to reprogram them.

  PROM：只能被编程一次。EPROM：可擦写可编程ROM，紫外线光照清除单元内容，可擦写次数数量级1000。E2PROM：电子可擦除PROM，可以直接在印制电路卡上编程，可擦写次数数量级10^5。FLASH：闪存，基于EEPROM。（固态硬盘SSD基于闪存）

(3) Accessing main memory

• Read transactions: Transferring data from main memory to the CPU.
• Write transactions: Transfer data from the CPU to main memory.
• Bus: A group of parallel conductors that can carry addresses, data, and control signals.

• Read TRANSACTION statement: MOVL A,%eax

  三个步骤：-CPU将地址A放到存储器总线。         -主存从总线读出A，接收字x，然后将x放到总线上。         

• Write Transaction statement: MOVL%eax,a

  三个步骤：-CPU将地址A放到存储器总线，主存读出这个地址，等待接收数据字。         -CPU将数据字y放到总路上。         -主存从总线读数据字y，并将它存储在地址A。

(4) disk storage

20145321 "Information Security system Design Fundamentals" 7th Week Study Summary