The difference between RAM, SRAM and FLASH

　　

There are two categories, one is called static RAM (SRAM/StaticRAM), very fast SRAM, is the fastest storage equipment now, speaking, reading and writing, but the price is more expensive, so only used in very demanding requirements, such as the CPU level of buffer, the secondary buffer.Another is called Dynamic RAM (Dynamic RAM/DRAM), DRAM retain data time is very short, speed ratioSRAMSlow, but it is faster than any of the ROM, but DRAM prices SRAM is a lot cheaper, computer memory is DRAM.DRAM is divided into a lot of kinds, common mainly include FPRAM/FastPage, EDORAM, SDRAM, DDR RAM, RDRAM, SGRAM and WRAM, here are one kind of DDR RAM.

DDR RAM (the Date to RAM) is also called DDR SDRAM, this improved RAM and SDRAM is basic same, different places is that it can read and write in a clock data twice, which makes the data transmission Rate doubled.This is the computer with the most memory, and it has a cost advantage, in fact, beat the Intel another standard - Rambus DRAM memory.On many high-end graphics CARDS, also equipped with high-speed DDR RAM to increase bandwidth, it can greatly improve the pixel rendering ability of 3 d accelerator card.

Memory works:

Memory is used to store the current data and programs are used, we mentioned the computer's memory refers to the dynamic memory (DRAM), dynamic memory in the so-called "dynamic", refers to when we writing data to DRAM, over a period of time, the data will be lost, so you need to set an additional circuit for a memory refresh operation.Specific work process is like this: a DRAM the storage unit of storage is 0 or 1 depends on whether there is electricity, have a charge on behalf of the 1, there is no charge on behalf of 0.But over time, on behalf of a capacitor will discharge, on behalf of zero capacitance will absorb the charge, this is the reason why data loss;Refresh operation regularly check the capacitance, if the battery is more than half of the full power, is that it represents 1, and the capacitance is full of electricity;If the battery is less than 1/2, thinks that its representative 0, and the capacitance discharge, to maintain the continuity of data.

　　

SRAM register is used to store information, so once the power lost, all data will be lost, as long as the power supply, its data will always exist, don't need to dynamically refresh, so called static random access memory.

Above is mainly used in the system memory, large capacity, do not need to still save the data when the power is cut off.

　　

PSRAM, static random access memory.DRAM storage has a single transistor, and the traditional has six transistor SRAM memory cell with two or four transistor - load resistor SRAM storage cell is very different, but it is similar to the stability of SRAM interface, internal DRAM architecture give PSRAM some than low - power 6 tsram outstanding advantages, such as lighter volume, price more advantage.In whole SRAM market at present, 90% of the manufacturers in the production of PSRAM components.Over the past two years, the market important SRAM/Samsung, Cypress, Renesas, Micron PSRAM suppliers and Toshiba, etc.

　　

PSRAM is pseudo SRAM, internal memory particles with SDRAM particles are similar, but the external interface with SRAM similar, do not need to be as complex SDRAM controller and refresh mechanism, PSRAM interface is the same with SRAM interface.

PSRAM capacity of 8 mbit, 16 mbit, 32 mbit, etc., capacity not as high density SDRAM, but certainly is much better than the capacity of SRAM, speed support emergency mode, not slow, WINBOND. Hynix, Coremagic, MICRON, CY has supplies manufacturers, such as price than the same volume of SDRAM only slightly more expensive, many cheaper than SRAM.

PSRAM is mainly used in mobile phones, PDA,. MP3/4, PDA, PMP, GPS receivers and other consumer electronics products, compared with an SRAM (with 6 t technique), PSRAM is 1 t + 1 c technique, so the smaller in volume, at the same time, the PSRAM I/O interface with SRAM. Same on capacity, there are 4 MB, 8 MB, 16 MB, 32 MB and 64 MB and 128 MB.Compared with SDRAM, PSRAM much lower power consumption.So for a certain cache capacity of a lot of portable products is a good choice.

　　

FLASH memory is also called the FLASH, it combines the strengths of the ROM and RAM, not only has the electronic can erase programmable block (EEPROM) performance, power will not lose data at the same time can be quickly read data (NVRAM advantage), U disk and MP3 player is the memory.In the past 20 years, the embedded system has been using ROM (EPROM) as their storage devices, however, in recent years, Flash comprehensive instead of ROM (EPROM) on the status of the embedded system, used for storing Bootloader and operating system or program code or directly when use hard disk (U disk).

Flash ROM is the use of the capacitance on the floating gate charge to store the information, because the floating gate leakage, so information when the power is still can be saved.Also because of its structure is simple so integration can do high, capacity can be very big.Erase Flash ROM before writing need electricity, and erase the different block with EEPROM to byte (bytes) for the unit, the Flash ROM only in sector (sector) as the unit.But when they write can byte as the unit.Flash ROM is mainly used in the BIOS, U disk, Mp3, etc to the large capacity and device that power is not lost.

At present there are two main types of Flash NOR Flash and NADN Flash.NOR Flash read and our common SDRAM read is the same, the user can run directly loading in NOR Flash code, which reduces the SRAM capacity and save the cost.

Not using NAND Flash memory random access technology, it reads is a read a piece of form, is often read 512 bytes at a time, using the technology of Flash is cheap.User cannot run directly on the NAND Flash code, so a lot of use NAND Flash development board in addition to using NAND Flah, also be on a small piece of NOR Flash to run the startup code.Generally small capacity of NOR Flash, because their reading speed, more used to store the operating system and other important information, and large capacity NAND Flash, embedded system is the most common NAND Flash applications using the DOC (Disk On Chip) and we usually use "Flash drive", can erase online.FLASH is currently on the market, mainly from Intel, AMD, Fujitsu and Toshiba, while production of NAND FLASH major manufacturers with Samsung and Toshiba.