Ram,sram,dram,sdram,ddr Ram,rom,prom,eprom,eeprom,nand Flash,nor FLASH the difference

RAM: It can be understood by literal means that SDRAM SRAM DRAM (These kinds of blue fonts below) can all be called Ram,random access memory (random access memory) abbreviation, the following is 51hei.com for everyone to tidy up the current memory of the difference.
SRAM: Static random memory, that is, it does not need to refresh the circuit, unlike dynamic random memory, the data should be refreshed every once in a while. But his integration is relatively low, not suitable for large-capacity memory, usually used in the processor's cache. Like s3c2440 's ARM9 processor, there are 4 K SRAM used for CPU start-up.
DRAM, dynamic random access memory, need to be constantly refreshed in order to save data. And it's a row-and-column address reuse, and many have page patterns.
SDRAM: Synchronous dynamic random memory, like the memory of the computer is the use of this RAM called DDR SDRAM. Its integration is very high, because it is dynamic, so there must be a refresh circuit, every time must be refreshed data. Its storage unit is not arranged linearly, it is paged. The memory inside the general embedded product is used SDRAM.
DDR SDRAM: Dual-channel synchronous dynamic RAM, need to refresh, fast, large capacity. (at present, the computer is the DDR memory for several generations.)
ROM: A generic term for read-only memory. The following red fonts are all part of the ROM
PROM: Programmable read-only memory, only write once, write the wrong will have to scrap, and now used very little, as if those costs of the lower cost of the OPT MCU is the use of this memory bar.
EPROM: erasable programmable memory, this thing is also more ancient, is the predecessor of the EEPROM, on the chip has a window, through ultraviolet radiation to erase data. It's very troublesome.
EEPROM: Electric erasable Programmable read-only memory, than the EPROM advanced point, you can use electricity to erase the face of data, is now used more memory, such as the 24CXX series of EEPROM.
Nandflash and Norflash are now more non-volatile flash memory. Nor adopts the parallel interface, its features read faster than the NAND happy many times, its program can be directly in nor inside the run. But its erase speed is relatively slow, low integration, high cost. Nor is the current capacity of about 2M, generally used in small code-size embedded products. There is also the Development Board on the ARM9 can be seen.
NAND, the use of a serial interface, the CPU from the inside to read the data is very slow, so generally used NAND flash memory must be the NAND inside the data first read into the inside, then the CPU can be executed. Just like the hard drive of a computer. But its integration is very high, my ARM9 development board above a 256M NAND is not a 2M nor half large, so the cost is very low. There is also the erase speed is also fast. Otherwise it would be really tragic, if erase a 2M nor to a minute, if the NAND erase speed is slower than nor, then erase a 256M nand is not a few hours. NAND is typically used on embedded products that run large operating systems, such as Linux, wince. Nor but can run, the Linux operating system can be cut to 2M, a product is only to run the system? User's application! In fact, a lot of times, an embedded product inside, the operating system accounted for only a small amount of storage space, most of them are for users to run the application. Like a computer, the hard disk is hundreds of G, but the windowns operating system occupies only a few grams of space.
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DRAM, SDRAM and SRAM the differences in memory commonly used by computers
Learning is summed up, from the point of time to summarize the next.
SRAM: Static RAM, do not refresh, the speed can be very fast, like the cache inside the CPU, are static RAM, the disadvantage is that a memory unit needs a lot of transistors, so the price is expensive, small capacity.
DRAM: Dynamic RAM, need to be refreshed, large capacity.
SDRAM: Synchronous dynamic RAM, need to refresh, faster, large capacity. (Previous computer-used memory strips)
DDR SDRAM: Dual-channel synchronous dynamic RAM, need to refresh, fast, large capacity. (at present, the computer is the DDR memory for several generations.)

Specific explanation one:
What is DRAM
The English full name of DRAM is ' Dynamic RAM ', which translates into Chinese as ' dynamically random memory '. DRAM is used for common data access. We often say how much memory, mainly refers to the capacity of DRAM.
What is SRAM
The English name of SRAM is ' static RAM ', which translates into Chinese as ' stationary random memory '. SRAM is primarily used to make caches.
What is SDRAM
SDRAM's English name is ' synchronous DRAM ', translated into Chinese is ' expansion of data output memory ', which is faster than the average DRAM and Edo RAM, it has gradually become the standard memory configuration of the PC.
What is the cache
The English intent of the Cache is ' storage ', which is usually made using SRAM, and it is faster than DRAM to exchange data with the CPU, so it is called "cache", or "cache". Because the CPU information processing speed is often more than the other parts of the message transfer speed, so the use of general DRAM as information memory often put the CPU waiting state, resulting in a waste of resources. The cache was created to solve the problem. After the operating system is started, the CPU is often called in the dram of some system information temporarily stored in the cache, later when the CPU needs to call this information, first to the cache to find, if found, directly from the cache read, This can save a lot of time by using the cache's high-speed performance. Most CPUs integrate a certain amount of cache in themselves, and are generally referred to as ' first-level cache ' or ' built-in caches '. This part of the memory and CPU information exchange speed is the fastest, but small capacity. Most motherboards are also integrated with the cache, commonly referred to as ' Level two cache ' or ' external cache ', which is larger than the built-in cache capacity, typically up to 256K, and now some motherboards are already using 512K~2M cache. In the latest Pentium two-generation CPUs, a first-level cache and a level two cache have been integrated, when the cache on the motherboard can only be called a ' level three cache '.
What is flash memory
Flash memory currently on the motherboard of the BIOS is mostly made of flash memory, translated into Chinese is ' flashing memory ', which is often referred to as ' flash memory ', referred to as the ' memory '. This memory can be upgraded directly to the BIOS by adjusting the voltage on the motherboard.
Explain why DRAM needs to be refreshed, SRAM does not need:
This is due to the type of RAM design, DRAM uses a T and an RC circuit, resulting in capacitance damage leakage and slow discharge. So a regular refresh is required to keep the data
Specific explanation two:
DRAM, dynamic random access memory, need to be constantly refreshed in order to save data. And it's a row-and-column address reuse, and many have page patterns.
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. SDRAM Although the operating frequency is high, but the actual throughput rate to be discounted. Take PC133 as an example, its clock period is 7.5ns, when the CAs latency=2, it takes 12 cycles to complete 8 bursts of read operations, 10 cycles to complete 8 bursts of write operations. However, if you access Bank,sdram alternately, you can complete one read-write operation per cycle (except, of course, the flush operation). In fact, now the mainstream high-speed memory is Ssram (synchronous SRAM) and SDRAM (synchronous DRAM). Currently can be easily bought Ssram maximum capacity is 8mb/tablets, the maximum working speed is 166MHz, can easily buy SDRAM maximum capacity is 128mb/tablets, the maximum working speed is 133MHz.
SRAM is the abbreviation for static random access memory, which is a type of semi-conductor memory. "Static" means that the data stored in the SRAM is not lost as long as it does not power down. This is different from dynamic RAM (DRAM), where DRAM requires periodic refresh operations. Then, we should not confuse SRAM with read-only memory (ROM) and flash memory, because SRAM is a volatile memory that maintains data only if the power supply is kept continuously. "Random access" means that the contents of a memory can be accessed in any order, regardless of which location was previously accessed.
Each of the bits in the SRAM is stored in four transistors, and the four transistors comprise two cross-coupled reverse converters. This storage unit has two stable states, usually expressed as 0 and 1. Additional two access transistors are required to control the access of the storage unit during read or write operations. Therefore, a storage bit typically requires six mosfets. The symmetrical circuit structure allows SRAM to be accessed faster than DRAM. Another reason SRAM is faster than DRAM access is that SRAM can receive all address bits at a time, while DRAM uses the structure of row and column address multiplexing.
SRAM should not be confused with SDRAM, SDRAM stands for synchronous DRAM (synchronous DRAM), which is completely different from SRAM. SRAM should not be confused with Psram, Psram is a dram disguised as SRAM.
From the type of transistor, SRAM can be divided into bipolar and CMOS two kinds. In terms of function, SRAM can be divided into asynchronous SRAM and synchronous SRAM (Ssram). The access of asynchronous SRAM is independent of the clock, and the data input and output are controlled by the change of address. All accesses to the synchronous SRAM are started on the rising/falling edge of the clock. The address, data input, and other control signals are related to the clock signal.
DRAM: Dynamic random access memory that requires constant refresh to save data. And it's a row-and-column address reuse, and many have page patterns.
SRAM: Static random access memory, power-up, do not 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.
The main is that the storage unit structure is different, resulting in a different capacity. A DRAM storage unit requires approximately one transistor and one capacitor (excluding line readout amplifiers, etc.), while an SRAM storage unit requires approximately six transistors. DRAM and SDRAM due to the implementation process problems, the capacity is larger than SRAM, but read and write speed than SRAM.
One is static, one is dynamic, static is used to hold the information, and the dynamic is to use the electronic, or when the refresh to maintain.
Memory (ie RAM) can be divided into static random memory SRAM, and dynamic random memory dram two kinds. What we often call "memory" refers to DRAM. But SRAM people are very little contact.
SRAM is actually a very important kind of memory, it has a wide range of uses. The SRAM is very fast and can be read and refreshed in a fast
Data integrity. The internal SRAM uses the form of a bistable circuit to store data. So the circuit structure of SRAM is very complex. The cost of producing SRAM of the same capacity is much higher than that of DRAM. That is why it has limited its development. So at present SRAM is basically only used for the first level cache inside the CPU and the built-in level two cache. Only a small number of network servers and routers can use SRAM.

Reprinted from: Http://www.100ask.org/bbs/forum.php?mod=viewthread&tid=12937&extra=page%3D1

Ram,sram,dram,sdram,ddr Ram,rom,prom,eprom,eeprom,nand Flash,nor FLASH the difference