What is the principle of U disk storage

U disk, as we live and work in the essential mobile storage device, we can say is indispensable to us, to help us store some important data files, but such an important device we know how much about it? Now let's go to the interpretation of the U disk storage principle, so that we are more familiar with its working principle.

Flash (Flash Memory) disk is a USB interface without the need for a physical drive miniature high-capacity mobile storage products, we call him U disk, is a non-volatile storage, with the advantages of turning off the power can still save the data, and at the same time can be repeated read and write and read and write speed, the unit volume of the maximum amount of data can be stored, as well as low-power characteristics and other advantages. Its storage physical mechanism is actually a new type of EEPROM (electrically erasable programmable read-only memory). It is a type of SCM (semiconductor memory).

Early SCMs used typical transistor triggers as storage bits, plus selection, read and write circuits to form the memory. Modern SCM using ultra-large-scale integrated circuit process made of memory chips, each chip contains a considerable number of storage bits, and then by a number of chips constitute memory. At present, the main material widely used in SCM is metal oxide field effect tube (MOS), including PMOS, NMOS, CMOS three categories, especially NMOS and CMOS is the most widely used.

RAM (Random Access Memory), is a semiconductor memory. RAM must work in the case of power, otherwise it will lose the stored information. RAM is divided into DRAM (dynamic) and SRAM (static) two kinds, we are now commonly used in the PC memory that is SDRAM (synchronous dynamic RAM), which needs to be charged at a certain frequency in the process of operation (refresh) in order to maintain the information. DDR DDR2 memory is also belongs to the SDRAM. SRAM does not need to be refreshed frequently and costs more than DRAM, and is mainly used in the CPU's integrated cache.

PROM (programmable ROM), on the other hand, can only be written to once and cannot be changed after writing.

EPROM (Erasable PROM) This EPROM can only read information during normal operation, but can erase existing information with ultraviolet light and write information at high voltage on specialized devices.

EEPROM (electrically erasable PROM), the user can read and write operations through the control of the program.

Flash memory is actually a type of EEPROM. Generally MOS gate (Gate) and channel spacing for the insulation of the oxide layer (gate oxide), and Flash Memory features in the control gate (Control gate) and the channel between a layer called "floating gate" (floating gate) of the material. Thanks to this floating gate, Flash Memory can quickly complete three basic operation modes: read, write, and erase; and even in environments where power is not supplied to the memory, the floating gate can be used to preserve the integrity of the data.

The electrons in the cells of a Flash Memory chip can be restored to their normal state by a higher voltage electronic area.1 Flash Memory utilizes an internal closure circuit, which not only allows the electronic area to act on the entire chip, but also allows for pre-setting of "blocks" (blocks). At the same time as setting the block, the target area of the chip is erased for re-writing. While traditional EEPROM chips can only erase one byte at a time, Flash Memory can erase one block or the entire chip at a time, and Flash Memory operates at a much faster speed than traditional EEPROM chips.

MSM (Magnetic Surface Memory) is the use of non-magnetic metals or plastics as a substrate, on the surface of which is coated, plated, deposited or sputtered a layer of very thin, high permeability, hard moment magnetic material of the magnetic surface, with the magnetic layer of the two remanent state of the magnetic layer to record information "0" and "1". ". The substrate and the magnetic layer are collectively referred to as the magnetic recording medium. Depending on the shape of the recording medium, it can be called magnetic card memory, magnetic tape memory, magnetic drum memory, and magnetic disk memory. The widely used MSM in computers today are disk and tape memories. Hard disks are MSM devices.

ODM (Optical Disk Memory) is similar to MSM in that a thin layer for recording is coated on a substrate to form the recording medium. The difference is that the circular sheet of the substrate is made of Plexiglas, which has a very low thermal conductivity and is highly heat resistant. In the surface of the recording layer and then coated or deposited protective thin layer to protect the recording surface. The recording thin layer has two types of non-magnetic and magnetic materials, the former constitutes the optical disk media, the latter constitutes the magnetic optical disk media.

ODM is the current auxiliary storage in the highest density of recording memory, storage capacity is very large and easy to replace the disk. The disadvantage is that the storage speed is one order of magnitude lower than the hard disk. ODMs with similar speeds to hard disks have been produced. cd-rom, dvd-rom, etc. are common ODMs.