| 1 内存的组成 | ||||
| 1.1 | PCB印刷线路板： | 是内存颗粒固定和连接外部电路的基板，常见的是4层或6层PCB板； | ||
| 1.2 | 内存颗粒 | 内存的核心元件； | ||
| 1.3 | 内在颗粒封装方式 | 目前主流的是BGA封装方式 | ||
| 1.4 | 内存接口 | 金手指，由众多金黄色的导电触片组成； | ||
| 1.5 | ||||
| 2 内存分类 | ||||
| 时钟频率与数据传输率 | 针脚数 | 电压 | ||
| SDRAM | 1:01 | |||
| DDR | 1:2(2倍预取2-bit Prefetch) | 184 | 2.5-2.8v | |
| DDR2 | 1:4(4倍预取） | 240 | 1.8v | |
内存（Memory）也被称为内存储器，其作用是用于暂时存放CPU中的运算数据，以及与硬盘等外部存储器交换的数据。只要计算机在运行中，CPU就会把需要运算的数据调到内存中进行运算，当运算完成后CPU再将结果传送出来，内存的运行也决定了计算机的稳定运行。 内存是由内存芯片、电路板、金手指等部分组成的。
内存又称主存，是CPU能直接寻址的存储空间，由半导体器件制成。内存的特点是存取速度快。内存是电脑中的主要部件，它是相对于外存而言的。我们平常使用的程序，如Windows操作系统、打字软件、游戏软件等，一般都是安装在硬盘等外存上的，但仅此是不能使用其功能的，必须把它们调入内存中运行，才能真正使用其功能，我们平时输入一段文字，或玩一个游戏，其实都是在内存中进行的。就好比在一个书房里，存放书籍的书架和书柜相当于电脑的外存，而我们工作的办公桌就是内存。通常我们把要永久保存的、大量的数据存储在外存上，而把一些临时的或少量的数据和程序放在内存上，当然内存的好坏会直接影响电脑的运行速度。
3 内存总线频率与CPU FSB频率的匹配
FSB800MHz的CPU：2个DDR400；
there are several types of ROM
1 PROM:one-time programmable ROM,once programmed,the content can't be changed;
2 EPROM-Erasable PROM.the content can be erased under certain UV light.
3 Flash,or EEPROM:electrical earsable PROM.the content can be erased by electrical pulses.
user may reprogram it on board.flash is a very good place to store BIOS;
SRAM is increduably expensive.
the first IC RAM cell in the history was a Flip-Flop made of 6 transistors.It has 2 stable states.representing 0 and 1.When a bit of data is written into this cell,it holds the state as long as the power is on;
As the size of RAM grows,the size of the memory cell reduces dramatically.Today's DRAM cell has only 1 transistor plus 1 small capacitor.The transistor acts as a switch that controls the charge or discharge.
the capacitor holds the bit of data-to store a 1 in the memory cell,the capacitor is filled with electrons.To store a 0,it is discharged.The problem with the capacitoris that it has a leak.the full charged cell will be empty within a few milliseconds.Therefore,the memory controller has to "refresh"the memory-read the memory and then write it right back.this refresh operation happens automatically thousands of times per second.refreshing takes time and slows down the memory.
DRAM made of 1 transistor and 1 capacitor in each cell.the small cell size means high integration density,low cost.But it need refreshing,so is lower,It is suitable for large memory space,such as systme memeory.
SRAM made of 4 or 6 transistors in each cell.It doesn't need refreshing.This makes SRAM significantly faster than DRAM.However,because it has more parts,a static memory cell takes up a lot more space and consumes more power.Therefore,you get less memory per chip,and that makes SRAM a lot more expense.It is used for fast,small memory,such as cache.