Concepts: primary storage, secondary storage, cache, Ram, SRAM, DRAM, Rom, prom, EPROM, EEPROM, CDROM, flash memory

Source: Internet
Author: User

Memory, also known as memory, is one of the important components in the computer and serves as a bridge to communicate with the CPU. All programs in the computer run in the memory, so the memory performance has a great impact on the computer. Memory (memory) is also called internal memory. It is used to temporarily store computing data in the CPU and data exchanged with external memory such as the hard disk. As long as the computer is running, the CPU transfers the data to be computed to the memory for computation. After the computation is completed, the CPU sends the result, the memory operation also determines the computer's stable operation. Memory is composed of memory chips, circuit boards, and gold fingers.


Secondary storage is a hard disk that we usually talk about in a narrow sense. It is scientifically an external memory (it needs to exchange data with it through an I/O system, also known as a secondary memory ). Large storage capacity, low cost, slow access, and permanent offline storage of information. It mainly includes magnetic surface storage, floppy disk storage, tape storage devices, and disc storage devices.


Cache high-speed buffer memory is a special storage subsystem, where frequently used data is copied to facilitate quick access. Memory's high-speed buffer memory stores the content of frequently accessed Ram locations and the storage addresses of these data items. When the processor references an address in the memory, the cache checks whether the address exists. If the address exists, the data is returned to the processor. if the address is not saved, regular memory access is performed. Because high-speed buffer memory is always faster than the primary RAM memory, when the access speed of Ram is lower than that of the microprocessor, high-speed buffer memory is often used.


Random Access Memory (RAM) is mainly used to store programs and data during computer operation. programs to be executed or data to be processed must be first loaded into RAM, data can be read from or written to the device. Ram features that the data in Ram can be used repeatedly when the computer is powered on, and is updated only when new data is written to it. After a power failure, the data in Ram disappears.


SRAM is short for static RAM. It is a type of memory with static access function. It can store internal storage data without refresh the circuit. The SRAM can store the data stored in the internal memory without refresh the circuit. The DRAM (Dynamic Random Access Memory) needs to be refresh and charged once every other time, otherwise the internal data will disappear. Therefore, the SRAM has high performance, but the SRAM also has its disadvantages, that is, it has a low degree of integration. The DRAM memory with the same capacity can be designed to be of a smaller size, but the SRAM requires a large volume and consumes a large amount of power. Therefore, the SRAM memory on the motherboard occupies part of the area.


Rom (read only memory) read-only memory refers to a memory that can only read data from the device but cannot write data into it. The data in the Rom is compiled by the designer and the manufacturer in advance to solidify some programs in it, the user cannot change at will. Rom is mainly used to check the configuration of computer systems and provide the most basic input/output (I/O) programs, such as the CMOS chip storing BIOS parameters. Rom is characterized by the existence of data in the memory after the computer is powered off.


Prom (programmable read-only memory)-programmable read-only memory, also called one-time programmable (OTP) Rom "one-time programmable read-only memory", is a read-only memory that can be operated by a program. The primary feature is that data can be written only once. If the data is burned into an error, the data can only be decommissioned.


The Erasable Programmable Rom (Erasable Programmable ROM) chip can be erased and written repeatedly, solving the drawback that the PROM chip can only be written once. The EPROM chip has an obvious feature. In its ceramic encapsulation, a glass window is opened. Through this window, you can see its internal integrated circuit, the ultraviolet rays can reach the internal chip through this hole to erase the data in it. To complete the chip erasure operation, the EPROM eraser is used. A dedicated programmer is used to write data in the EPROM, and a certain programming voltage (VPP = 12-24 V, depending on the chip model ). The EPROM model starts with 27, for example, 27c020 (8*256 K) is a piece of 2 m
Bits capacity of the EPROM chip. After the EPROM chip writes data, it also needs to block the window with an opaque sticker or tape to avoid damage to the data caused by ultraviolet radiation. When the EPROM chip is in the blank state (after being erased with UV light), the data of each internal storage unit is 1 (high level ).


EEPROM (systically erasable programmable read-only memory), electrically erasable programmable read-only memory-a storage chip that does not lose data after power loss. EEPROM can erase existing information on a computer or a dedicated device and re-program it. It is usually used in plug-and-play scenarios. EEPROM (electro-erasable programmable read-only memory) is a user-changeable read-only memory (ROM) that can be erased and reprogrammed (rewritten) by a voltage higher than ordinary EEPROM ). Unlike the EPROM chip, the EEPROM can be modified without being removed from the computer. In an EEPROM, when the computer is used, it can be re-programmed frequently. the lifetime of the EEPROM is an important design consideration parameter. One special form of EEPROM is flash memory. Its application is usually the voltage in the PC to erase and re-program.
EEPROM, which is generally used for plug-and-play ). It is often used in interface cards to store hardware configuration data. It is also commonly used in "Hardware locks" to prevent unauthorized copying of software.


A CD-ROM (compact disc read-only memory) is a read-only disc used on a computer. This type of CD can only write data once, and the information will be permanently stored on the CD, and the information will be read through the CD drive when used. The CD format was originally designed for the storage and playback of music. In 1985, the Yellow Book standards developed by Sony and Philips allowed the format to adapt to a variety of binary data. Some CD-ROM stores both music and computer data, the CD-ROM of music can be played by the CD player, computer data can only be processed by the computer.


Flash Memory, also known as flash memory, is a long-lived non-volatile memory that maintains the stored data information when powered off, data deletion is not measured in a single byte but in a fixed block (Note: nor flash is stored in bytes .), The block size is generally kb to 20 mb. Flash memory is a variant of the electronic erasable read-only memory (EEPROM). Unlike flash memory, it can be deleted and rewritten horizontally in bytes instead of the entire chip, in this way, the flash memory is faster than the eeprom update speed. Because the data can still be stored during power-off, flash memory is usually used to save settings, such as in the computer BIOS (Basic Input and Output Program), PDA (Personal Digital Assistant) save data in digital cameras, etc.



1. random-access memory (Random Access Memory): memory is an important part of the computer's composition structure. Memory is a component used to store programs and data. For computers, only with memory can they have the memory function to ensure normal operation. There are many types of memory, which can be divided into primary memory and secondary memory [or internal memory and external memory] based on their purposes. The primary memory is short for memory. Internal computer plays an important role. The memory is generally a semiconductor storage unit. Because Ram is the most important memory in memory, we usually call it memory. Memory is the place where the storage program and data are stored. For example, when we use WPS to process documents, when you type a character on the keyboard, it is stored in the memory, when you choose to save the disk, the data in the memory will be stored in the hard (magnetic) disk. Ram can read or write data from it. When the power of the machine is off, the data stored in the machine will be lost. We usually purchase or upgrade the memory stick for computer memory, and the memory stick (SIMM) is a small circuit board that integrates the ram Integrated Block, which is inserted into the memory slot of the computer, to reduce the space occupied by the ram Integrated Block. At present, there are 128 M memory, 256 M memory, and 512 M memory. 2. SDRAM (synchronous DRAM): synchronous dynamic random memory. At present, the 168-line 64-bit bandwidth memory basically uses the SDRAM chip, the operating voltage is 3.3v, the access speed is as high as 7.5ns, And the Edo memory is as fast as 15ns. The ram and CPU are controlled at the same clock frequency, so that the ram and CPU are synchronized with the external frequency and the wait time is canceled. Therefore, its transmission rate is faster than Edo dram. The storage speed of the RAM chip is faster than that of the ROM chip, however, it is slower than the cache speed. The advantages and disadvantages of dynamic RAM and static RAM are that static RAM uses a bistability trigger to remember information. Dynamic RAM uses the gate capacitor in the mos circuit to remember information. Because the charge on the capacitor will leak and needs to be supplemented regularly, dynamic RAM needs to set a refresh circuit. However, compared with static RAM, dynamic RAM features high integration, low power consumption, and low cost. It is suitable for large-capacity storage. Therefore, the primary memory usually uses dynamic RAM, while the high-speed buffer memory (cache) uses static RAM. In addition, the memory is also used in graphics cards, sound cards, CMOS and other devices to act as the device cache or save fixed programs and data.

SDRAM: synchronous dynamic random access memory, which synchronizes dynamic random memory. Synchronization refers to the synchronization of clock for memory operations. Internal Command sending and data transmission are based on it; dynamic means that the storage array needs to be constantly refreshed to ensure that data is not lost. Random means that the index data is not stored in a linear order, but the data is read and written by freely specifying the address.

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