Common Memory Concepts: RAM, SRAM, SDRAM, ROM, EPROM, EEPROM, flash memory can be divided into many kinds, which can be divided into RAM (random access memory) and ROM (read-only memory) according to the loss of the power-down data, where the RAM access speed is relatively fast , but the data is lost after power-down, and the data is not lost after the ROM is dropped.
In the microcontroller, RAM is mainly to do the runtime data memory, Flash is mainly program memory, EEPROM is mainly used in the program to save some need to lose the power of the data.
FLASH: A single-chip computer to run the program stored somewhere.
SRAM: Storage of the temporary data generated during the operation of the microcontroller.
EEPROM: Depending on the needs of the user, generally used to store some parameters of the system, these parameters may need to be modified, or may not be modified.
Rom and Ram refer to the semiconductor memory, ROM is the abbreviation of Read only memory, RAM is the abbreviation of random Access memory. Rom can still hold data while the system is powered off, and ram usually loses data after power-down, typical RAM is the memory of the computer. In addition, some variables are put into RAM, some of the initial data such as LCD to display the content interface, are placed in the flash area (that is, the ROM area previously said), EEPROM can not be used, mainly to save some running data, after power loss and not lost
RAM can also be divided into SRAM (static ram/quiescent memory) and DRAM (Dynamic ram/dynamics memory). SRAM is the use of bistable trigger to save information, as long as not power down, the information will not be lost. DRAM uses a MOS (metal oxide semiconductor) capacitor to store the information, so it has to maintain the information by charging the capacitor continuously, so the cost, integration, and power consumption of the DRAM are significantly better than SRAM. SRAM is very fast, is currently the fastest to read and write storage devices, but it is also very expensive, so only in a demanding place to use, such as the CPU of a buffer, two-level buffer. DRAM retains data for a short period of time, slower than SRAM, but it is faster than any ROM, but from the price of DRAM is much cheaper than SRAM, computer memory is DRAM.
How memory Works: Memory is used to store data and programs that are currently in use (i.e., executing), the memory of the computer we refer to is dynamic memory (that is, DRAM), what is called "dynamic" in dynamic memory, which means that when we write the data to DRAM, the data is lost after a period of time, Therefore, an additional circuit is required for the memory refresh operation.
The specific work process is this: a DRAM storage unit is stored in 0 or 1 depending on whether the capacitor has an electric charge, an electric charge represents 1, and no charge represents 0. But a long time, representing 1 of the capacitance will discharge, representing 0 of the capacitance will absorb the charge, this is the reason for the loss of data; The refresh operation periodically checks the capacitance, if the charge is greater than 1/2 of the charge, it is considered to represent 1, and the capacitance is fully charged, if the charge is less than 1/2, it is considered to represent 0 To maintain the continuity of the data.
And what is commonly said SDRAM is a dram, it is synchronous dynamic memory, using a single system clock to synchronize all the address data and control signals. Using SDRAM not only improves system performance, but also simplifies design and provides high-speed data transfer. Often used in embedded systems.
There are many types of ROM, the prom is a programmable rom,prom and EPROM (erasable programmable ROM) The difference is that the prom is a one-time, that is, after the software is poured, it can not be modified, this is an early product, it is now impossible to use, The EPROM is a kind of universal memory by wiping out the original program by ultraviolet light irradiation. Another type of EEPROM is the electronic wipe, the price is very high, the write time is very long, writing is very slow. Mobile phone software is generally placed in the EEPROM, we call, some of the last dialed number, is currently in the SRAM, not immediately write through records (call records saved in the EEPROM), because there is very important work (call) to do, if written, long wait is to let users endure.
Flash is also a non-volatile memory (power loss will not be lost), it is easy to erase, access speed, has greatly replaced the traditional EPROM status. Many people call it flash ROM because it has the same features as ROM power-down that is not lost. Flash memory, also known as Flash, combines the advantages of ROM and RAM, not only with electronic erasable programmable (EEPROM) performance, but also without power loss data can be quickly read data (NVRAM advantage), u disk and MP3 used in this kind of memory. In the past 20 years, embedded systems have been using ROM (EPROM) as their storage devices, but in recent years Flash has replaced the ROM (EPROM) in the embedded system, Used as storage bootloader as well as operating system or program code or directly on the hard disk (USB drive).
There are two main flash and Flash and NADN Flash. Nor Flash read the same as our common SDRAM read, the user can directly run the code loaded in nor flash, which can reduce the capacity of SRAM and thus save costs. NAND Flash does not take the memory of random read technology, its reading is in a single read a fast form, usually read 512 bytes at a time, the use of this technology flash relatively inexpensive. The user cannot directly run the code on NAND flash, so a lot of the development boards using NAND flash use a small nor flash to run the startup code in addition to the NAND Flah.
Generally small-capacity with nor Flash, because of its fast reading speed, much to store the operating system and other important information, while the large capacity of NAND flash, the most common NAND flash applications are embedded system using the doc (disk on Chip) and our usual "flash disk", can be erased online. The current flash on the market mainly comes from Intel,amd,fujitsu and Toshiba, while the main manufacturers of NAND Flash are Samsung and Toshiba.
Differences between RAM, SRAM, SDRAM, ROM, EPROM, EEPROM, flash memory
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