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Foreword
When Toshiba of Japan first invented the semiconductor memory chip, they thought it was as fast as the flash of light when taking a picture, so it was named flash memory ( Flash). The most common forms we use today are NOR flash and NAND flash. According to different scenarios, we use different memories. NOR flash memory is usually used in embedded systems, while mobile phone internal storage, PC hard drives, USB flash drives, etc. use NAND flash memory. The data stored in these devices is typically read more often than written, but the frequency of writes is still relatively high, so NAND flash is the more common choice.
1 Flash physical structure
1.1 What is Flash?
Flash is a non-volatile storage device. Corresponding to volatile storage devices, the data stored in Flash Memory will not be lost even if the power is turned off. In addition to Flash, other common non-volatile storage devices include magnetic disks and optical disks. Volatile storage devices, as their name suggests, lose data when power is removed. Common volatile storage devices include memory sticks, such as DDR5, etc.
Minimum storage unit
The smallest storage unit of flash memory is the "Transistor-Gate-Drain" (TGD) structure. In this structure, electrons on the gate can control the charge flux between the drain and source, allowing data to be stored and read.