1, RAM (random access memory) :( belong volatile memory)
SRAM: Static random access memory, a data storage six transistors, high power consumption, large area
DRAM: Dynamic Random Access Memory, a transistor and a capacitive storage data an inexpensive simple, needs to be refreshed
SDRAM: synchronous dynamic random access memory, clocks need to be synchronized, need to be refreshed
DDR (double data rate) SDRAM: dual-channel synchronous SDRAM. A clock data can be read two
2, the storage hierarchy:
Register (the Register, also translated Register) : in a processor, a processor used to set the function, primarily where the set value "is temporarily stored."
Cache memory (Cache memory, the translated version of the cache, cache, cache, cache memory; Taiwan translated into cache.) : Within the processor, when executing the program program with local "temporary storage" of information, usually SRAM production.
Main memory (Main Memory) : external to the processor, "temporary storage" program with local information, usually in DRAM production, has now improved to SDRAM or DDR.
A secondary memory (Memory Assistant) : external to the processor, "persistent storage" local program information, comprising: a flash memory, disk drive, optical disk drive, tape drive and the like.
3、NAND flash 和 nor flash
nor flash: Write slow (very slow rub) to read fast. Provide complete addressing and data bus allows random access to any area on the memory byte address. CPU may start directly, you do not need to be copied to the RAM. Suitable for small-capacity memory to start the firmware.
nand flash: To read data in NandFlash above, to add the master and the external circuit design; flash; high storage density and low cost; suitable for large-capacity storage device. 【SSD】
Differences: both NAND and NOR may read bytes, but written in NAND page units, and each NOR random write byte; the Flash NOR parallel, the Flash NAND serial; isolated as the Flash NOR address and data lines, and is multiplexed NANDFlash;
【supplement】
emmc: the equivalent of NandFlash + master control IC, external interface protocol and SD, TF card as; provides a standard interface and flash memory management;