1. Introduction to Flash
1. Development
2. Contrast the difference
2.1 RAM and ROM
RAM (random access memory, random access memory, is characterized by arbitrary byte read and write, power-off loss
ROM (read only memory, read-only memory, similar to Flash SD card and the like, used to store things, power-down not lost, No random address access, only block access
2.2 Magnetic storage and flash storage
Magnetic storage . Advantages: mature technology and cheap price; Disadvantages: slow read and write speed, poor reliability, cannot be used for
flash storage of embedded devices . Advantages: fast read and write speed, and no physical loss
2.3MLC and SLC
SLC , the technology is relatively early, high reliability, the disadvantage is that the capacity is not large (or the capacity is too expensive, generally SLC Nand is less than 512MB);
MLC , the technology is relatively new, immature, poor reliability, the advantage is that the capacity can be It is very cheap to make it big, and now basically MLC technology is being developed
2.4nand and SD card, MMC card, MicroSD, TF card
nand , just do the most basic read and write interface to the storage unit, and then require an external SoC to provide a flash read and write controller to perform read and write timing with the flash. Defects: 1. The timing of read and write interface is complicated. 2. There is no internal bad block processing mechanism, and the SoC itself needs to manage the bad blocks of the Flash; 3. The Flash interfaces of various manufacturers are inconsistent , and even the Flash interfaces of different models and series of the same manufacturer are inconsistent, which results in product upgrades. very troublesome.
The sd card has more unified external packaging and interfaces than the direct Nand chip . Cards have a unified standard, such as SD cards are released in accordance with the SD specification. These specifications specify the SD card's read/write speed, read/write interface timing, read/write command set, card size, number of pins and definitions. The advantage of this is that SD cards from different manufacturers can be used in common.
2.5nand and iNand, MoviNand, eSSD and SD card, etc.
SD card , external expansion card for a long time, the card slot may have poor contact and become unreliable.
inand , advantages: 1. Learning from SD card, there is a unified interface standard (including pin definition, physical package, interface timing). 2. Learn from the original Nand, and release it in the form of a chip instead of a card ; 3. There is a built-in Flash management module, which provides functions such as bad block management , which makes the management of Nand easier.
2.6 The difference between SD card and MicroSD, MMC, TF respectively
The MMC
(1) standard is earlier than the SD standard, and the SD standard is compatible with the MMC standard.
(2) MMC card can be read and written by SD card reader, while SD card cannot be read and written by MMC card reader.
MicroSD , only the size is different, the transmission is exactly the same as the principle.
TF card
(1) In terms of appearance, SD card is large and TF card is small; in terms of use, SD card is used for digital cameras, etc., while TF card is widely used in mobile phones, GPS, etc.;
(2) In terms of time, SD card was launched in 1999, TF card The card was launched in 2004; the SD card was jointly launched by Japan's Panasonic, Toshiba and SanDisk of the United States, and the TF card was jointly launched by Motorola and SanDisk.
(3) The SD card has write protection and the TF card does not. The TF card can be converted into an SD card through the card sleeve.
Reference: Teacher Zhu's Embedded Course