About Sram,dram,sdram, and Norflash,nandflash

about the SRAM , DRAM , SDRAM

SRAM : Static random memory, do not need to refresh the circuit, which makes static RAM faster than dynamic RAM, but, because he contains more devices, low integration, not suitable for large capacity of memory, generally used in the processor's cache, SRAM speed is very fast, In the fast read and refresh to ensure data integrity, SRAM circuit structure is very complex, the production of the same capacity SRAM than the cost of DRAM is much higher, because of this, so that its development is limited, in the s3c2440 chip, there are 16KB instruction Cache (instruction cache) 16KB data cache and 4KB boot internal SRAM, but we can use only 4KB boot internal SRAM, This 4KB SRAM is used to load the uboot from the Nandflash boot.

DRAM : Dynamic random memory, every once in a while to refresh data to ensure that the data is not lost, SDRAM: Synchronous dynamic random memory, which is commonly referred to as memory, memory is the code of execution space, to execute the program, synchronization refers to the data read and write need the clock to synchronize, DRAM and SDRAM due to the implementation process problems, capacity is larger than SRAM, but read and write speed than SRAM, general embedded products inside memory are used SDRAM, computer memory is also used this RAM called DDR SDRAM, in the mini2440 Development Board, S3C2440 's external connection is two 32MB SDRAM, which is memory. Note that it is not inside the chip, but on the outside of the chip,

Buffer memory

The cache is inside the CPU, inside the CPU outside, before always feel inside the CPU inside, this is a misunderstanding,

Cache is the buffer of data exchange, when a piece of hardware to read data, will first look for the necessary data from the cache, if found is directly executed, if not found, then from memory, because the cache storage speed than memory faster, so the role of caching is to help the hardware run faster, The fastest cache in the computer is the L1 and L2 cache embedded in the CPU, the memory of the video card is the cache for the graphics card, and the 16M or 32M cache is also on the hard disk.

The cache is only a small portion of the data in memory, so the CPU to the cache to find data, there will also be found, when the CPU or back to the memory to find data, so that the rate of the system slowed down, but the CPU will be the data copied into the cache, so that the next time do not go to the memory to fetch ，

Norflash and the Nandflash

Norflash: adopts the parallel interface, has the independent address line and the data line, its biggest characteristic is the Norflash inside the program can run directly, does not have to read the code to the system RAM, the mini2440 Development Board is the 2M Norflash,

Nandflash : The use of serial interface, address lines and data lines are common IO lines, similar to the computer's hard disk, the CPU from the inside of the speed of reading data is very slow, the inside of his code can not directly run, to run the need to nandflash inside the data read into the memory, and then the CPU can execute, But his integration is very high, the cost is very low,

About Sram,dram,sdram, and Norflash,nandflash