1.RAM
RAM (Random Access Memory) random access, used to store and save data. It can be read and written at any time, and RAM is usually used as a temporary storage medium for the operating system or other running programs (may be called system memory). RAM cannot retain data when the power is turned off, and RAM memory can be further divided into two categories: static RAM (SRAM) and dynamic memory (DRAM). Running memory (mobile phone)
2.ROM
ROM (Read Only Memory) is a read-only memory, even if the power is turned off, the ROM can retain data. However, once the data is written, it can only be changed by special methods or at all. (data/system/cache/.)
3.Flash Rom
FLASH memory, also known as flash memory, which combines the advantages of ROM and RAM, not only has the performance of electronically erasable and programmable (EEPROM), but also will not lose data at the same time. Data can be read quickly (an advantage of NVRAM), which is the memory used in U disk 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 ROM (EPROM) in embedded systems and is used to store Bootloaders and operating systems or programs. code or use it directly as a hard disk (U disk).
At present, there are two main types of Flash, NOR Flash and NADN Flash. The reading of NOR Flash is the same as the reading 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, and its reading is carried out in the form of reading one block at a time, usually 512 bytes at a time. Flash using this technology is relatively cheap. Users cannot directly run the code on NAND Flash, so many development boards that use NAND Flash use a small NOR Flash to run the startup code in addition to using NAND Flash.
Generally, small-capacity NOR Flash is used because of its fast reading speed and is mostly used to store important information such as operating systems, while large-capacity NAND FLASH is used. The most common NAND FLASH application is the DOC (Disk On Chip) used in embedded systems. And we usually use "flash disk", which can be erased online. At present, the FLASH on the market mainly comes from Intel, AMD, Fujitsu and Mxic, while the main manufacturers of NAND Flash are Samsung, Toshiba and Hynix.
4.
EEPROM EEPROM (ELECTRICALLY ERASE PROGRAMMABLE READ ONLY MEMORY) power-down storage
5. Flash emulated EEPROM
The EEPROM emulation mode is used in IP Core based ESCs with a non-volatile memory (NVRAM) attached or integrated to a micro controller. The ESC configuration and the device description can be stored in the Flash of the micro controller, eg, together with the program or other configuration data. An additional external EEPROM chip for the system is not needed any more if EEPROM emulation is used.
Gossip: The
Difference Between Memory and Registers
Fundamentally , registers are not physically the same as RAM.
The general register refers to the D trigger derived from the basic RS flip-flop structure, which
is a structure composed of some NAND gates, which everyone has seen in digital electronics;
and RAM has its own process, generally 1Bit is composed of six MOS tubes. constitute. Therefore,
the physical structure of the two is different, which also leads to the different performance of the two. Register
access is fast, but occupies a large area. On the contrary, RAM has a small footprint and
low power, and can be made into a large-capacity memory, but the access speed is relatively slow.
1.
The register exists in the CPU, and the speed is very fast and the number is limited;
the memory is the memory, the speed is slightly slower, but the number is large;
when the computer does the operation, the data must be read into the register to operate.
2. The
memory includes registers. The
memory includes ROM and RAM
registers, which are only used for temporary storage. They are temporarily allocated. After the power is turned off, the contents inside are gone.
Basic concepts of sector block flash page
Sector : sector: the smallest unit of operation on hardware (disk), which is the unit of data transfer between the operating system and block device (hardware, disk)
Block: block consists of one or more sectors , is the smallest unit of operation in software (OS, file system); the virtual file system of the operating system reads a block from the hardware device, which actually reads one or more sectors from the hardware device. For file management, each Multiple blocks corresponding to a file may be discontinuous; blocks are eventually mapped to sectors, so the size of blocks is generally an integer multiple of the sector. Different file system blocks can use different sizes. The operating system will open up memory in the memory and store the blocks in the so-called block buffer.
page:4 sectors = 1 page