Ram, Rom, and Flash Memory categories

DRAM, Dynamic Random Access Memory, need to constantly refresh to save data, and the row and column addresses are reused, many of which have the page mode.

SRAM, static random access memory. When powered on, data does not need to be refreshed, and data will not be lost. In addition, it is generally not reused by row and column addresses.

SDRAM, synchronous DRAM, that is, data read/write requires clock synchronization. DRAM and SDRAM have a large capacity due to technical issues. However, the speed of reading and writing is not as high as that of SRAM, but now the speed of SDRAM is also very fast, and the clock seems to have been 150 MB. The read/write cycle is smaller than 10ns.

Static Memory and synchronous dynamic memory (high speed and large sdramcapacity)

 

Ssram is the abbreviation of synchronous static random access memory, that is, synchronous static random access memory.

 

Dram of each unit of capacity uses a small transistor and occupies a small area, while SRAM uses a relatively large area with a large number of transistors; DRAM needs to be constantly refreshed to maintain the stored data, but SRAM does not need it. DRAM has a long access clock interval, while SRAM is fast and time-consuming. DRAM consumes low power, high power consumption of SRAM.

At present, the price of the same capacity of SRAM is about 8 times that of SDRAM, and the area is nearly 4 times larger. Therefore, SRAM is often used for fast storage of low-capacity Ram requirements, such as cache (cache ), for example, the L1 cache in the CPU and the L2 cache on the motherboard are usually only several hundred kb.

Wiring can also comply with the needs of high-speed design. For details, refer to the manufacturer's design specifications.

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 speed of SRAM is very fast. It is the fastest storage device for reading and writing, but it is also very expensive, therefore, it can only be used in demanding scenarios, such as CPU Level 1 buffering and level 2 buffering. The other is dynamic RAM (Dynamic RAM/Dram). DRAM retains data for a short period of time and is slower than SRAM, but it is 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 ddr sdram. The improved Ram is basically the same as that of SDRAM. The difference is that it can read and write data twice at a clock, this doubles the data transmission speed. 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 used to erase the original program through ultraviolet radiation and is a general 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, the mobile phone software is usually placed in the EEPROM. When we call, some of the last dialing numbers are temporarily stored in the SRAM, rather than writing the pass record immediately (the call record is stored in the EEPROM ), at that time, there was a lot of important work (CALLS) to do. If you write data, a long wait would be 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 after power failure, and data can be quickly read (NVRAM advantage), which is used in USB flash drives and MP3. 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, it is used to store bootloader, operating system or program code, or directly used as a hard disk (USB flash disk ).

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 512 bytes at a time, usually in a low cost. Users cannot directly run the code on NAND Flash. Therefore, many development boards that use NAND Flash use a small nor flash to run the startup code in addition to NAND flah. (Nor flash capacity is small, but can be directly read; NAND Flash capacity is large, but cannot be directly read)

Nor flash is usually used for small capacity. Because of its fast reading speed, it is used to store important information such as the operating system, while NAND Flash is used for large capacity, the most common nand flash application is the DOC (Disk On Chip) used in 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.

 

Bucket: at present, ramtron's fram mainly includes two categories: Serial fram and parallel FRAM. The serial fram is divided into the fm24 series of I2C two-line mode and the fm25 series of SPI three-line mode. Serial fram is compatible with the traditional 24-and 25-type E2PROM pins in a timely manner and can be directly replaced. FRAM has the advantages of Ram and Rom, which are fast in read/write and can be used like non-volatile memory. E2PROM is wiped 1 million times, and the amount of ferroic can reach 10 billion times.

 

It is mainly used in data applications that require fast and repeated storage.