A storage system refers to a computer system composed of various storage devices that store programs and data, control components, and equipment (hardware) and algorithms (software) that manage information scheduling.
The storage system is one of the important components of the computer. The storage system provides the ability to write and read the information (programs and data) needed by the computer to achieve the computer's information memory function. A multi-level storage architecture of registers, cache, main memory and external memory is often used in modern computer systems.
From the operating system, the emergence of different types of memory is to achieve the classic memory architecture: multi-level cache structure, in order to match the high-speed CPU. From the internal registers of the CPU, to the high-speed cache, to the main memory, then to the disk, and finally to the tape, the speed is getting slower and slower, but the price is getting cheaper. The memory architecture including DSP is also divided into three levels. The first level is the internal registers of the CPU, the second level is L1P and L1DRAM, and the third level is L1SRAM. L1 and L2 are all on-chip RAM, and can also be passed through the EMIF interface. (64X+) or XINTFT interface (28 series) to expand off-chip memory, in short, the speed is getting slower and slower.
Memory can be divided into external memory and internal memory according to purpose. External storage is usually a magnetic medium or an optical disc, which can store information for a long time. Memory refers to the storage components on the motherboard, which are used to store the currently executing data and programs. They are only used to temporarily store the programs and data. The data will be lost if the power is turned off or power is cut off.
RAM
RAM (random access memory, random access memory). The contents of the storage unit can be taken out or stored at will as needed, and the access speed is independent of the location of the storage unit. This kind of memory will lose its storage content when power is off, so it is mainly used to store short-term use programs. According to the different storage information, random access memory is divided into static random access memory (Static RAM, SRAM) and dynamic random access memory (Dynamic RAM, DRAM).
SHAME
SRAM (Static RAM, static random access memory), does not need to refresh the circuit, the data will not be lost, and generally it is not row and column address multiplexing. However, its integration level is relatively low, and it is not suitable for large-capacity memory, which is generally used in the cache of the processor. ARM9 processors like S3C2440 have 4K of SRAM for CPU startup.
SRAM is actually a very important memory, and it has a wide range of uses. SRAM is very fast and can maintain data integrity during fast read and refresh. SRAM uses a bistable circuit to store data. So the circuit structure of SRAM is very complicated. The cost of manufacturing SRAM with the same capacity is much higher than that of DRAM. Because of this, its development has been restricted. Therefore, at present, SRAM is basically only used for the first level cache inside the CPU and the built-in second level cache. Only a small number of web servers and routers can use SRAM.
DRAM
Dynamic RAM, dynamic random access memory, must refresh the data at regular intervals to save the data. And the row and column addresses are multiplexed, and many have page modes. SDRAM is one of them.
SDRAM
SDRAM (Synchronous DRAM, synchronous dynamic random access memory), that is, data reading and writing need clock to synchronize. The storage units are not arranged linearly, but are paged.
DRAM and SDRAM have larger capacity than SRAM due to process problems. But the read and write speed is not as good as SRAM.