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EEPROM

Flash Memory

Flash Memory- HowStuffWorks

Wikipedia - Flash Memory

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EEPROM wikipedia

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If you’re not familiar with flash memory, you should be. It’s poised to make a whole host of older technologies obsolete – all to your advantage. You probably own some and are not even aware of it. If you have a digital camera, newer cell phone, USB memory, Ipod or Palm PC - a flash memory is built into every one of these devices. Flash memory is not a new technology – it has been around for the last 20 years. It was invented by Dr. Fujio Masuoka while working for Toshiba in 1984. What’s new is low price and high availability. $50 will get you a decent quality memory that will have enough space for most needs. MP3 fanatics will want larger capacity models as song libraries frequently run over 1 GB. It’s predicted in the long run these devices will even replace your computer’s hard drive.

Flash memory is a type of EEPROM chip. EEPROM, or sometimes known as E^2PROM, is Electrically Erasable Programmable Read-Only Memory. It is a special type of PROM . It is similar to flash memory, sometimes called flash EEPROM.the difference is that EEPROM requires data to be written/erased one byte at a time whereas flash memory allows data to be written and erased in blocks, making flash memory faster. Many of the modern computer's BIOS are stored on a flash memory chip so that it can be easily updated if necessary, which is called a flash BIOS. The flash memory is popular in modems because it allows the modem manufacturer to support new protocols as they are modernized. that is able to be erased by being exposed to an electrical charge. Like other types of PROM, EEPROM retains it's contents even after it is turned off. Also, like other types of ROM, it is not as fast as RAM .

Your computer's BIOS chip is the most common form of flash memory. Removable, solid-state "storage devices" are becoming increasingly popular. CompactFlash and SmartMedia are two of the most popular and well known products, especially as "electronic film" for digital cameras. There is also things like flash drives, Sony's Memory Stick, memory cards for game systems (N64, Dreamcast, and Sony's Playstation). There are several different reasons to use flash media as opposed to a hard disk. 1) Flash memory is noiseless, 2) it allows faster access, 3) it is smaller in size, 4) it is lighter, and 5) it has no moving parts.

If you have used a digital camera, then you know that even after switching off the camera, information about the photos you have taken is still available. Devices like mobiles, PDA, digital cameras, camcorders, digital audio recorders, smart pagers, GPS systems, etc. store information in a device called flash memory.It works like a hard drive but is more compact and has fewer power requirements. Flash memory allows data to be written and erased from multiple locations. This ensures a much faster speed. Examples of flash memory devices are multimedia cards, secure digital cards, floppy disks, and flash cards.

How does it work?

Flash memory can be read or programmed one byte or word at a time in a random access pattern. Flash memory comprises cells or transistors made of a thin oxide layer. The cell has two transistors at its ends called the floating gate and the control gate. These operate on the 0 and 1 value concept. Applying an electric charge to the circuit runs Read/Write actions. Flash memory works using the tunneling principle to change the position of electrons in the floating gate. A charge of 10 to 13 volts is usually applied to the floating gate. Once charged, the electrons in the floating gate move to the other side of the oxide layer and change the charge to negative thus forming a barrier between the control and the floating gate. The threshold value of the charge regulates the functioning. When the flash memory is blank, then the value is one. Once a byte is programmed, it must be erased before it can be changed. Compared to conventional hard disk drives, flash drives are much more expensive.

The electrons in a flash memory chip can be returned to normal by using an electric field (a higher voltage charge). The flash memory uses in-circuit wiring to be able to apply the elctric field to either the whole entire chip or just certain parts of the cip called blocks. THis erases the targeted area of the chip, and can be re-written. Flash memory works much faster than traditional EEPROMs because instead of erasing one byte at a time, it erases a block or the entire chip, and then rewrites it. Flash memory is non-volatile, which means that it does not need power to maintain the information stored in the chip.

Though EPROMs are a big step up from PROMs in terms of reusability, they still require dedicated equipment and a labor-intensive process to remove and reinstall them each time a change is necessary. Also, changes cannot be made incrementally to an EPROM; the whole chip must be erased. Electrically Erasable Programmable Read-Only Memory (EEPROM) chips eliminate the biggest drawbacks of EPROMs. In EEPROMs: The chip doesn't have to removed to be rewritten, the entire chip does not have to be completely erased to change a specific portion of it, and changing the contents does not require additional dedicated equipment. Instead of using UV light, you can return the electrons in the cells of an EEPROM to normal with the localized application of an electric field to each cell. This erases the targeted cells of the EEPROM, which can then be rewritten. EEPROMs are changed 1 byte at a time, which makes them versatile but slow. In fact, EEPROM chips are too slow to use in many products that make quick changes to the data stored on the chip. Manufacturers responded to this limitation with Flash memory, a type of EEPROM that uses in-circuit wiring to erase by applying an electrical field to the entire chip or to predetermined sections of the chip called blocks. Flash memory works much faster than traditional EEPROMs because it writes data in chunks, usually 512 bytes in size, instead of 1 byte at a time.