什麼是DRAM？

動態隨機存取記憶體(Dynamic Random Access Memory，DRAM)屬於一種揮發性記憶體(volatile memory)，主要的作用原理是利用電容內儲存電荷的多寡來代表一個二進位位元(bit)是1還是0。由於在現實中電容會有漏電的現象，導致電位差不足而使記憶消失，因此除非電容經常周期性地充電，否則無法確保記憶長存。由於這種需要定時刷新的特性，因此被稱為「動態」記憶體。相對來說，「靜態」記憶體(SRAM)只要存入資料後，縱使不刷新也不會遺失記憶。 DRAM的記憶單元與SRAM相比，DRAM的優勢在於結構簡單，每一個位元的資料都只需一個電容跟一個電晶體來處理，相比之下在SRAM上一個位元通常需要六個電晶體。因此，DRAM擁有高密度，低成本的優點，但是它也有存取速度較慢，耗電量較大的缺點。

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Dynamic random access memory

Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor電容器 within an integrated circuit積體電路IC. Since real capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory.

The main memory (the "RAM") in personal computers is Dynamic RAM (DRAM), as is the "RAM" of home game consoles (Playstation, Xbox 360 and Wii), laptop, notebook and workstation computers.

The advantage of DRAM is its structural simplicity: only one transistor電晶體 and a capacitor are required per bit, compared to six transistors in SRAM. This allows DRAM to reach very high density. Unlike flash memory, it is volatile memory (cf. non-volatile memory非消失性記憶體NVM), since it loses its data when the power supply is removed. The transistors and capacitors used are extremely small—millions can fit on a single memory chip.

http://en.wikipedia.org/wiki/Dynamic_random_access_memory