RAM是指隨機存取存儲器，是所有計算機中都有的一種數據存儲。它為電腦提供了讀/寫空間，存入CPU(中央處理器)中。內存的主要目的是為了存儲臨時數據和指令所需的常規操作，加快CPU的存取時間。RAM是一個不穩定的內存,所以一旦關閉電源，存儲指令和數據會丟失。
 
隨機存取存儲器是如何讓工作的—How RAM works
 
RAM是“隨機存取”，因為您可以一如既往的訪問任何存儲單元，如果你能辨別相交的行和列單元。在RAM中，存儲單元可以以任意順序訪問。
 
動態隨機存取存儲器(DRAM)是最常見的計算機內存，晶體管和電容配對形成記憶細胞代表一位的數據。晶體管像開關一樣控制電路，使內存芯片閱讀電容器或更改其狀態。與此同時，電容器包含信息0或1。
 
RAM stands for Random Access Memory which is a type of data storage used in all computers. It provides space to your computer to read/write to be accessed by the CPU (Central Processing Unit). The main purpose of RAM is to store temporary data and instructions required for it regular operation, resulting in faster access time for the CPU. RAM is a volatile memory, so stored instructions and data are lost once the power is turned off.
 
隨機存取存儲器是如何讓工作的—How RAM works
 
RAM is considered "random access" because you can access any memory cell unswervingly if you can identify the row and column that intersect at that cell. Memory cells in RAM can be accessed in any order.
 
The most common form of computer memory which is the Dynamic RAM (DRAM), a transistor and a capacitor are paired to form a memory cell representing a single bit of data. The transistor operates as a switch that enables the control circuitry on the memory chip to read the capacitor or changes its state. Meanwhile, the capacitor contains the bits of information 0 or 1.
 
A capacitor is similar to a small bucket that is capable of storing electron. The bucket is filled with electrons by storing a 1 in the memory cell and it is emptied by storing a 0. The problem with the capacitor bucket is that it has a leak, thus for dynamic memory to work, either the CPU or the memory controller has to proceed and recharge all of the capacitors containing a 1 before they release. By doing this, the memory controller reads the memory and then writes it back, resulting in the refresh operations taking place repeatedly thousands of times per second.
 
DRAM works by transferring a charge through the appropriate column to turn on the transistor at each bit in the column. The row lines hold the state capacitor should take on when writing, while the sense-amplifier decides the level of charge in the capacitor when reading. If it is more than 50%, it reads as 1; else, it reads as 0.#p#分頁標題#e#
 
Static RAM uses a completely different technology. The main difference is it never has to be refreshed which make SRAM a lot faster than DRAM. Furthermore, Static RAM is faster and expensive whereas DRAM is opposite. Therefore, SRAM is used to make CPU's speed sensitive cache, while DRAM forms the larger system RAM space.
 
隨機存取存儲器的類型—Types of RAM
 
SRAM (Static RAM)
 
Static RAM also known as SRAM is the first type of RAM and it does not need to be refresh. SRAM can be accessed at around 10 nanoseconds. SRAM is more costly and may require up to four times the size for a given amount of data than DRAM. The structure of SRAM restricts them to maximum data capacity of 256kb, therefore, SRAM is used in system cache.
DRAM (Dynamic RAM)
 
DRAM was created to overcome the restriction of SRAM. Even though, DRAM chips provide much slower access time compare to SRAM, it can store several megabytes of data on a single chip. DRAM stores each bit of data in a separate capacitor inside an integrated circuit and need to be refresh periodically. However, with the constant refresh, it can make access even much slower and causes the DRAM chips to draw extra power from the computer. Thereafter, DRAM is used as main memory in the computer because of it high capacity and low cost.
EDO RAM (Extended Data Output RAM)
 
EDO RAM is the leading RAM in the mid-1900s. When one piece of data is being sent to the processer, another is being retrieved from the RAM module. The usual accessed time for EDO DRAM is 60 ns.
SDRAM (Synchronous DRAM)
 
SDRAM is around twice as fast as EDO RAM because it is able to run the speed at the speed of the system bus (up to 100-133 MHz). Besides, SDRAM allow new memory access before the proceeding access is accomplished.
RDRAM (Rambus RAM)
 
The name Rambus originated from a company named Rambus Inc that manufactured it and RDRAM has a data transfer rate of 800MHz. RDRAM can only used in computers with special RDRAM channels and slots.
DDR RAM (Double-data Rate RAM)
 
DDR RAM is used to replace SDRAM which it can double the rate speed at which standard SDRAM can process. The data transfer rate of DDR RAM is between 100 and 200MHz.
DDR RAM
 
DDR2 RAM
 
DDR2 RAM is the newer version of DDR RAM. The data transfer rate is between 200 and 400MHz. the significant features in DDR2 RAM are higher speed, density and require lower power than DDR RAM.