EEPROM is the acronym for electrically erasable programmable read-only memory, and is alternatively written as E2PROM. It is pronounced as e-e-prom or e-squared. It refers to a nonvolatile memory that is used in computers as well as other electronic devices that need to save data even when the computer is disconnected from the power source. This is unlike random access memory (RAM), which loses data when the computer is powered off. Actually, EEPROM can be erased and programmed with electrical pulses using a process known as Fowler–Nordheim tunneling to experts. A new EEPROM contains no data and has to be programmed before it can be used. EEPROM data cannot be rewritten selectively, and the data inside the entire chip has to be erased and rewritten (one byte at a time) to update the contents. Therefore, EEPROM is used in many BIOS chips to maintain the system settings. The advent of EEPROM made it possible for manufacturers to update the BIOS program, something that was not possible in the past. (Earlier, outdated BIOS chips could only be updated by getting a completely new motherboard.) An updated BIOS chip is as good as new, and is referred to as flash BIOS, because of the way the EEPROM is updated using electrical charges or flashes. However, if for some reason larger amounts of data need to be stored, it would make more economic sense to use flash memory instead. Other uses of EEPROM include storing user-programmable information, including;
* Digital satellite receiver control data
* Programming information on a compact disc
* Video cassette recorder (VCR) programming information
In a computer monitor, the data can be copied from the EEPROM to the microprocessor by the monitor itself. This way, the EEPROM lets the microprocessor know at which frequency the monitor is going to operate. It also stores the current settings of the monitor. Whenever there is a change in the monitor settings, the microprocessor will update the settings in the EEPROM, and when it is switched on again, the settings that were stored are used to set up the monitor for operation. EEPROM has its quirks. It is much slower than RAM, and so it is not the appropriate memory for applications with dynamic read/write requirements, such as a digital camera or a flash card. And this is where flash memory comes in. This is a new breed of EEPROM that differs from the EEPROM discussed earlier in that data in a flash memory may be selectively written. Data may also be erased and rewritten in blocks, as opposed to one byte at a time, which makes it faster. Overall, EEPROM takes more die per area than flash memory for comparable capacity simply because each cell would require a write, read, and erase transistor whereas in flash memory the erase circuits are shared by the cells. There are several other related nonvolatile memory technologies, including FeRAM and MRAM. Although these technologies are slowly replacing EEPROM in some applications, they still have insignificant control of the market and are likely to cater to niche applications for the foreseeable future.
For more information on EEPROM, refer to this article.