"Turn" RAM Daquan-dram, SRAM, SDRAM relations and differences

ROM and ram refer to the semiconductor memory, ROM is the abbreviation of Read only memory, RAM is the abbreviation of random Access memory. Rom can still hold data while the system is powered off, and ram usually loses data after power-down, typical RAM is the memory of the computer.

There are two main types of RAM, a static RAM, which is very fast, is the fastest storage device to read and write, but it is also very expensive, so it is only used in very demanding places, such as CPU Ram/sram, level two buffering. Another known as Dynamic RAM (Ram/dram), DRAM retains data for a short time and is slower than SRAM, but it is faster than any ROM, but the price of DRAM is much cheaper than SRAM, and computer memory is DRAM.

DRAM, dynamic random access memory, need to be constantly refreshed in order to save data. And it is the row and column address reuse, many have page mode.

SRAM, static random access memory, power-up, no need to refresh, data is not lost, and, generally, is not the row and column address reuse.

SDRAM, synchronous dram, i.e. the reading and writing of data requires a clock to synchronize. DRAM and SDRAM are larger in capacity than SRAM due to the realization of process problems. But read and write slower than SRAM, but now, SDRAM speed is already very fast, the clock seems to have 150 trillion. So the read-write period is less than 10ns.

SRAM is static memory, SDRAM is synchronous dynamic memory

The DRAM per unit capacity uses less transistors and occupies a small footprint, while the SRAM is used with more transistors to occupy a relatively large number of faces; the DRAM needs to be constantly refreshed to maintain the stored data, SRAM is not required, and the DRAM has a long access clock interval, and the SRAM is faster and shorter. DRAM consumes low power and SRAM consumes large power.

at present, the same capacity SRAM price is about 8 times times the SDRAM, the area is nearly 4 times times, so SRAM is often used for fast storage of low-capacity RAM requirements, such as cache, such as the internal CPU L1 cache and the motherboard L2 cache, Generally only hundreds of K.

wiring can also comply with the requirements of high-speed design, specific reference to the manufacturer design specifications.

There are many types of dram, common mainly fpram/fastpage, Edoram, SDRAM, DDR RAM, RDRAM, Sgram, and Wram, which are described in one of the DDR RAM. DDR RAM (Date-rate RAM) is also known as DDR SDRAM, which is basically the same as the improved RAM and SDRAM, except that it can read and write two of times on a single clock, thus doubling the data transfer speed. This is the most used memory in the current computer, and it has a cost advantage, in fact defeating Intel's other memory standard-rambus DRAM. On many high-end graphics cards, high-speed DDR RAM is also available to increase bandwidth, which significantly improves the pixel rendering capabilities of 3D accelerator cards.

There are many types of ROM, the prom is a programmable rom,prom and EPROM (erasable programmable ROM) The difference is that the prom is a one-time, that is, after the software is poured, it can not be modified, this is an early product, it is now impossible to use, and EPROM is a kind of universal memory that erases the original program through ultraviolet irradiation. Another type of EEPROM is the electronic wipe, the price is very high, the write time is very long, writing is very slow.

For example, mobile phone software is generally placed in the EEPROM, we call, some of the last dialed number, is currently in the SRAM, not immediately write through the record (call record saved in the EEPROM), because there is very important work (call) to do, if written, The long wait is unbearable to the user.

Flash memory, also known as Flash, combines the advantages of ROM and RAM, not only with electronic erasable programmable (EEPROM) performance, but also without power loss data can be quickly read data (NVRAM advantage), u disk and MP3 used in this kind of memory. In the past 20 years, embedded systems have been using ROM (EPROM) as their storage devices, but in recent years Flash has replaced ROM (EPROM) in embedded systems as a storage Bootloader as well as the operating system or program code or directly using the drive (USB stick).

There are two main flash and Flash and NADN Flash. Nor Flash read the same as our common SDRAM read, the user can directly run the code loaded in nor flash, which can reduce the capacity of SRAM and thus save costs. NAND Flash does not take the memory of random read technology, its reading is in a single read a fast form, usually read 512 bytes at a time, the use of this technology flash relatively inexpensive. The user cannot directly run the code on NAND flash, so a lot of the development boards using NAND flash use a small nor flash to run the startup code in addition to the NAND Flah.

generally small-capacity with nor Flash, because of its fast reading speed, much to store the operating system and other important information, while the large capacity of NAND flash, the most common NAND flash applications are embedded system using the doc (disk on Chip) and we usually use the "flash disk" And can be erased online. The current flash on the market mainly comes from Intel,amd,fujitsu and Toshiba, while the main manufacturers of NAND Flash are Samsung and Toshiba.

http://blog.csdn.net/huleide/article/details/5506698

"Turn" RAM Daquan-dram, SRAM, SDRAM relations and differences