The difference between EEPROM, EPROM, FLASH, SRAM, DRAM, SDRAM and SDRAM
EEPROM, EPROM, FLASH are all based on a floating gate transister structure. The floating gate of the EPROM is in an insulating silica layer, and the charged electrons can only be excited by the energy of ultraviolet rays, and the unit of EEPROM is composed of FLOTOX (Floating-gate tuneling oxide transister) and an additional transister, which can be read/written by the unit due to the characteristics of FLOTOX and the two-tube structure. Technically, FLASH is achieved by combining EPROM and EEPROM technologies, and many FLASH uses avalanche thermionic injection to program, erasing using Fowler-Nordheim tuning like EEPROM. But the main difference is that FLASH provides large or whole block erasures of the chip, which reduces the complexity of the design, and it can do without the extra Tansister in the EEPROM unit, so it can achieve high integration, large capacity, and the floating grid process of FLASH is also different, and the writing speed is faster.
In fact, for users, the main difference between EEPROM and FLASH is
1。 EEPROM can be erased by "bit", while FLASH can only be erased by large slices.
2。 EEPROM generally has a small capacity, and if it is large, EEPROM has no price advantage compared to FLASH. The stand alone EERPOM sold on the market is generally below 64KBIT, while FLASH is generally 8MEG BIT or above (NOR type).
3。 In terms of reading speed, it should not be the difference between the two, but EERPOM is generally used for low-end products, and the reading speed does not need to be so fast.
4。 Because the memory unit of EEPROM is two tubes and FLASH is one (except for SST, which is similar to two tubes), so in the case of CYCLING, EEPROM is better than FLASH, and there is no problem up to 1000K times.
In general, there is no big difference between EEPROM and FLASH for users, but EEPROM is a low-end product with low capacity and cheap price, but the stability is better than FLASH. But for the design of EEPROM and FLASH, FLASH is much more difficult, both in terms of process and peripheral circuit design.
Flash memory refers to "flash memory", the so-called "flash memory", which is also a non-volatile memory, which belongs to the improved product of EEPROM. Its biggest feature is that it must be erased by block (the size of each block varies, different manufacturers have different specifications), while EEPROM can erase only one byte at a time. At present, "flash memory" is widely used on PC motherboards to save BIOS programs and facilitate program upgrades. Another major application area is to use it as a subs服装, which has the advantages of shock resistance, high speed, no noise, and low power consumption, but it is not suitable to replace RAM, because RAM needs to be able to be rewritten byte-by-byte, which Flash ROM cannot.
ROM and RAM both refer to semiconductor memory, ROM is the abbreviation of Read Only Memory, and RAM is the abbreviation of Random Access Memory. ROM can still maintain data when the system is powered off, while RAM usually loses data after a power outage, and typical RAM is the memory of the computer.
There are two types of RAM, one is called static RAM (Static RAM/SRAM), SRAM is very fast, it is currently 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 level 1 buffer, level 2 buffer. The other is called dynamic RAM (Dynamic RAM/DRAM), DRAM retains data for a short time, and the speed is slower than 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, the common ones are FPRAM/FastPage, EDORAM, SDRAM, DDR RAM, RDRAM, SGRAM and WRAM, etc., here is an introduction to one of DDR RAM. DDR RAM (Date-Rate RAM), also known as DDR SDRAM, is basically the same as SDRAM, except that it can read and write data twice in one clock, which doubles the data transfer speed. This is the most used memory in computers today, and it has a cost advantage, in fact, beating another memory standard from Intel - Rambus DRAM. Many high-end graphics cards are also equipped with high-speed DDR RAM to increase bandwidth, which can greatly improve the pixel rendering capabilities of 3D acceleration cards.
There are also many kinds of ROMs, PROM is programmable ROM, the difference between PROM and EPROM (erasable programmable ROM) is that PROM is disposable, that is, after the software is injected, it cannot be modified, this is an early product, now it is impossible to use, and EPROM is through ultraviolet light to erase the original program, which is a universal memory. Another type of EEPROM is electronically erased, which is very expensive, has a long writing time and is very slow.
For example, mobile phone software is generally placed in EEPROM, we make a call, some of the last dialed numbers, temporarily exist in SRAM, not immediately written through the record (call records are saved in EEPROM), because there is very important work (call) to do at that time, if it is written, the long wait is unbearable for the user.
FLASH memory, also known as flash memory, combines the strengths of ROM and RAM, not only has the performance of electronic erasable programmable (EEPROM), but also can quickly read data without power loss (the advantage of NVRAM), which is used in USB flash drives and MP3s. For the past 20 years, embedded systems have been using ROM (EPROM) as their storage device, but in recent years Flash has completely replaced ROM (EPROM) in embedded systems as a storage bootloader and operating system or program code or directly as a hard disk (USB flash drive).
At present, there are two main types of Flash: NOR Flash and NADN Flash. NOR Flash reads the same as our common SDRAM reads, and 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 memory random read technology, its reading is carried out in the form of one read at a time, usually 512 bytes at a time, and Flash with this technology is cheaper. Users cannot directly run the code on NAND Flash, so many development boards using NAND Flash use a small piece of NOR Flash to run the boot code in addition to NAND Flah.
Generally, NOR Flash is used for small capacity, because of its fast reading speed, and is mostly used to store important information such as the operating system, while for large capacity NAND FLASH, the most common NAND FLASH application is DOC (Disk On Chip) used in embedded systems and the "flash disk" we usually use, which can be erased online. At present, the FLASH on the market mainly comes from Intel, AMD, Fujitsu and Toshiba, while the main manufacturers of NAND Flash are Samsung and Toshiba.
SRAM,DRAM,SDRAM
SRAM is the abbreviation of Static Random Access Memory, which means static random access memory in Chinese, which is a type of semiconductor memory. "Static" means that data stored in SRAM is not lost as long as the power does not go out. This is different from dynamic RAM (DRAM), which 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 is only able to hold data if the power supply remains continuous. "Random access" means that the contents of the memory can be accessed in any order, regardless of which location was previously accessed.
Each bit in the SRAM is stored in four transistors that make up two cross-coupled inverters. This storage cell has two steady states, usually represented as 0 and 1. Two access transistors are also required to control access to the memory unit during read or write operations. Therefore, a single memory bit typically requires six MOSFETs. The symmetrical circuit structure allows SRAM to be accessed faster than DRAM. Another reason why SRAM is faster than DRAM is that SRAM can receive all address bits at once, while DRAM uses a structure of row and column address multiplexing.
SRAM should not be confused with SDRAM, which stands for Synchronous DRAM, which is completely different from SRAM. SRAM should also not be confused with PSRAM, which is a type of DRAM disguised as SRAM.
In terms of transistor types, SRAM can be divided into two types: bipolar and CMOS. In terms of function, SRAM can be divided into asynchronous SRAM and synchronous SRAM (SSRAM). Access to asynchronous SRAM is clock-independent, and both data input and output are controlled by address changes. All access to synchronous SRAM is initiated on the rising/falling edge of the clock. Addresses, data inputs, and other control signals are all related to the clock signal.
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Posted on 11/15/2014 8:52:56 PM
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