Differences between Rom, SDRAM, Ram, DRAM, SRAM, and Flash

Rom and RAM are both semiconductor memory, Rom is short for read only memory, and Ram is short for random access memory. ROM can still maintain data when the system stops power supply, while Ram usually loses data after power loss. A typical Ram is the computer memory.
Ram has two categories: static RAM (static RAM/SRAM ), The fast speed of SRAM is the fastest read/write storage device. But it is also very expensive, so it is only used in demanding places, such CPU Level 1 buffer, level 2 buffer. Also known as dynamic RAM (Dynamic RAM/Dram ), DRAM retains data for a short time The speed is also slower than the speed of SRAM, but it is still faster than any Rom, but in terms of price DRAM is much cheaper than SRAM, and computer memory is dram. .
DRAM is divided into many types. Common types include fpram/fastpage, edoram, SDRAM, ddr ram, RDRAM, sgram, and wram. Here we will introduce a ddr ram. Ddr ram (date-rate RAM) is also called ddrsdram. The improved Ram is basically the same as SDRAM. The difference is that it can read and write data twice at a clock, this makes the data transmission speed
Double. This is the most widely used memory in computers, and it has a cost advantage. In fact, it beat Intel's other memory standard-Rambus DRAM. In many high-end graphics cards, high-speed ddr ram is also provided to increase the bandwidth, which can greatly improve the pixel rendering capability of the 3D accelerator card.
There are also many types of Rom. The difference between the prom and the EPROM is that the prom is one-time, that is, after the software is filled in, it cannot be modified. This is an early product and cannot be used now. The EPROM is wiped out by ultraviolet radiation. Program Is a general type of memory. Another type of EEPROM is an electronic interface. It has a high price, a long write time, and a low write speed.
For example, Mobile phone software is generally placed in the EEPROM , We Call. Some of the last dialing numbers are currently in the SRAM. Instead of writing the pass record immediately ( Call records are stored in the EEPROM ), Because at that time there was a lot of important work (CALLS) to do, if the write, a long wait is unbearable for users.
Flash Memory, also known as flash memory, combines the strengths of ROM and Ram, not only has the electronic Erasable Programmable (EEPROM) performance, data will not be lost due to power failure, and data can be quickly read (the advantage of NVRAM ), This memory is used in USB flash drives and MP3 files. . In the past 20 years, embedded systems have been using ROM (EPROM) as their storage devices. However, in recent years, Flash has completely replaced the position of RoM (EPROM) in embedded systems, used to store Bootloader and operating systems or programs Code Or directly use it as a hard disk (USB flash drive ).
Currently, there are two types of FLASH: nor flash and nadn flash. The reading of nor flash is the same as that of our common SDRAM. Users can directly run the code loaded in nor flash, which can reduce the capacity of SRAM and save costs. NAND Flash does not adopt the random read Technology of memory. It reads a block at a time, usually 512 bytes at a time. Flash with this technology is cheaper. Users cannot directly run code on NAND Flash. Therefore, many development boards that use NAND Flash use not only NAND flah, but also a small one. Norflash to run the startup code .
Average Nor flash is used for small capacity. Because of its fast reading speed, it is used to store important information such as the operating system. While the large-capacity NAND Flash is used, the most common nand flash application is the DOC (Disk On Chip) used by the embedded system and the "flash disk" we usually use, which can be erased online. Flash on the market is mainly from Intel, AMD, Fujitsu and toshba, while the main manufacturers of NAND Flash are Samsung and toshba.
Static random access memory is a type of semiconductor memory. Static means that data stored in SRAM will not be lost if no power is lost. This is different from dynamic RAM (Dram, DRAM needs to be refreshed periodically . Then, we should not confuse SRAM with read-only memory (ROM) and flash memory, because SRAM is a kind of volatile memory, it can maintain data only when the power supply is continuously supplied. "Random Access" means that the content of the memory can be accessed in any order, regardless of the location of the previous access.Each bit in the SRAM is stored in four transistors, which form two cross-coupled backbones. . This storage unit has two stable states, usually 0 and 1. In addition, two access transistors are required to control access to the storage units during read or write operations. Therefore, A storage space usually requires six Enis. . Symmetric circuit structure makes the access speed of SRAM faster than that of DRAM . Another reason why SRAM is faster than DRAM access is SRAM can receive all the address bits at a time, while DRAM uses the line address and column address multiplexing structure. . SRAM should not be confused with SDRAM, which represents synchronous DRAM, which is totally different from SRAM. SRAM should not be confused with psram either, Psram is a dram disguised as SRAM. .
From the transistor type, SRAM can be divided into bipolar and CMOS. In terms of functions, SRAM can be divided into asynchronous SRAM and synchronous SRAM (ssram ). Asynchronous SRAM access is independent of the clock, and data input and output are controlled by address changes. All accesses to the synchronized SRAM are started along the rise/fall of the clock. Address, data input, and other control signals are related to clock signals.