DRAM

Introduction

Dynamic random access memory (Dynamic Random Access Memory, DRAM) is a semiconductor memory, the main function of which is to use the amount of charge stored in the capacitor to represent whether a binary bit (bit) is 1 or 0. In reality, the transistor will have a leakage current phenomenon, resulting in the amount of charge stored on the capacitor is not enough to correctly determine the data, resulting in data corruption. Therefore, for DRAM, periodic charging is an inevitable requirement. Because of this feature that requires regular refresh, it is called "dynamic" memory. Relatively speaking, as long as the static memory (SRAM) stores data, it will not lose memory even if it is not refreshed.

Compared with SRAM, DRAM has the advantage of simple structure-each bit of data requires only one capacitor and one transistor to process, compared to six transistors for one bit on SRAM. For this reason, DRAM has a very high density, and the capacity per unit volume is high, so the cost is low. On the contrary, DRAM also has the disadvantages of slower access speed and higher power consumption.

Like most random access memory (RAM), since the data stored in the DRAM will disappear soon after the power is cut off, it belongs to a volatile memory (volatile memory) device.

Working principle

DRAM is usually arranged in a two-dimensional matrix with a capacitor and a transistor as a unit. The basic operation mechanism is divided into read (Read) and write (Write). When reading, first let Bitline (BL) charge to half of the operating voltage, and then turn on the transistor to allow BL and capacitor to share the phenomenon of charge sharing. If the stored value is 1, the BL voltage will be raised to more than half of the operating voltage by charge sharing. On the contrary, if the internally stored value is 0, the BL voltage will be lowered to less than half of the operating voltage. After the voltage of BL is obtained, the internal values of 0 and 1 are discriminated through the amplifier. When writing, the transistor will be turned on. If you want to write 1, the BL voltage will be increased to the operating voltage so that the operating voltage is stored on the capacitor. If you want to write 0, the BL will be reduced to 0 volts so that there is no charge inside the capacitor.

Random access memory

Random access memory (English: RandomAccessMemory, abbreviation: RAM), also called main memory, is an internal memory that directly exchanges data with the CPU. It can be read and written at any time (except when refreshed, see below), and it is very fast, usually used as a temporary data storage medium for the operating system or other running programs.

Main memory (main memory) is the main memory inside the computer, used to load various programs and data for the CPU to directly run and use. Due to its high cost performance and good scalability, DRAM is the most important part of general computer memory today. The main memory used in the production of computers in 2014 was mainly DDR3 SDRAM. Since 2016, DDR4 SDRAM has been gradually popularized. Notebook manufacturers such as ASUS and Acer have begun to replace DDR3L with DDR4 memory in notebook computers.