EEPROM (Electrically Erasable Programmable read only memory)Live erasable programmable read-only memory. It is a kind of memory chip with no data loss after a power failure. EEPROM can erase existing information and reprogram it on a computer or on a dedicated device. Usually used in Plug and Play.
EEPROM (Live Erasable Programmable Read-Write Memory) is a user-modifiable read-only memory
(ROM), which can be erased and reprogrammed (rewritten) by an action higher than the normal voltage. Unlike EPROM chips, EEPROM can be modified without having to be removed from the computer. In an EEPROM, when the computer is in use, it can be programmed repeatedly frequently, so the life of EEPROM is an important design consideration parameter. EEPROM is a special form of flash memory, which is usually used to erase and reprogram voltages in personal computers ;
In the early days of computer development, BIOS was stored in ROM (Read Only Memory). The internal data of ROM is burned in the manufacturing process of ROM. It can only be read and can not be changed. Once burned in, users can only verify the correctness of the written data and can not make any modifications. If any errors are found in the data, they must be discarded.
Make a new order. ROM is manufactured on the production line. Because of its high cost, it is usually only used in large-scale applications.
Because of the inconvenience of ROM manufacturing and upgrading, PROM (Programmable ROM) was invented later. Initially, PROM produced from the factory has no data inside. Users can write their own data in a special programmer, but this opportunity is only once. Once written, it can not be modified. If there is a mistake, the chip written can only be scrapped. PROM has the same characteristics as ROM, but its cost is higher than ROM, and the speed of writing data is slower than that of mass production of ROM. Generally, PROM is only suitable for small demand occasions or pre-production verification of ROM.
EPROM (Erasable Programmable ROM, erasable programmable ROM) chip can be erased and written repeatedly, which solves the problem that PROM chip can only be written once. EPROM chip has a distinct feature. There is a glass window on its front ceramic package. Through this window, we can see its internal integrated circuit. Ultraviolet radiation through the hole can erase the data inside the chip. EPROM eraser is used to complete the chip erasure operation. The data in EPROM should be written by a special programmer, and a certain programming voltage must be added when writing content to the chip (VPP = 12 ~ 24V, depending on the type of chip). EPROM models start with 27, such as 27C020 (8*256K) which is a 2M Bits capacity EPROM chip. After the EPROM chip is written into the data, the windows are sealed with opaque stickers or tapes to protect the data from the surrounding ultraviolet radiation.
Because of the inconvenience of EPROM operation, most of BIOS ROM chips on the motherboard are EEPROM (Electrical Erasable Programmable ROM). EEPROM erasure does not need to use other devices. It uses electronic signals to modify its content and uses Byte as the smallest unit of modification. It does not need to wash out all the data before it can be written. It completely gets rid of the bondage of EPROM Eraser and IC programmer. When EEPROM writes data, it still needs to use a certain programming voltage. At this time, it can easily rewrite the content with the special refresh program provided by the manufacturer, so it belongs to the dual-voltage chip. With the dual-voltage characteristic of EEPROM chip, BIOS can have good anti-virus function. When upgraded, jumper switch is hit to the “on” position, that is to say, the corresponding programming voltage is added to the chip, which can be easily upgraded. In normal use, jumper switch is hit to the “off” position to prevent CIH virus from illegally modifying BIOS chip. Therefore, there are still many motherboards using EEPROM as the BIOS chip and as a major feature of their motherboards.
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