Difference between eeprom and serial RAM

[Naumanpak]

I know its silly but I need to know the difference between 2 terms.

 

[srizbf]

eeprom is non volatile. ram is volatile.

 

[supercat]

I know its silly but I need to know the difference between 2 terms.

A serial RAM can write data as fast as it can be clocked in, and each byte may be written an unlimited number of times without "wearing out"; it will only retain its contents, however, as long as power is applied. Some designs combine a serial RAM with a battery.

An EEPROM will take about 5ms to write each byte or small groups of bytes (many can write up to 16 bytes at a time; some can write as many as 128), and will wear out if the same location is written too many times (the limit is usually between 100,000 and 10,000,000 cycles, with 1,000,000 being the most common number). Most EEPROMs allow individual bytes to be written without regard for their previous contents. An EEPROM will hold its contents indefinitely without power.

A serial flash will be similar to an EEPROM, except that "programming" (turning 1's to 0's) and "erasing" (turning 0's to 1's) are separate operations. The flash 'program' operation is fast, but can only operate upon parts of the chip that are blank; the 'erase' operation takes much longer (tens or hundreds of milliseconds), and has to operate on large blocks of the chip at once. A few flash chips allow a 256-byte erase command, but more commonly the minimum erase area is 4K. On some larger chips, the minimum erase area may be as much as 128K. If it's necessary to erase some information from a block while keeping other information, the information to be kept must be copied somewhere else. Serial flash chips are available in much larger sizes than EEPROM chips; 128Kx8 would be considered very large for a serial EEPROM and very small for a serial flash.