On Monday, January 17, 2000, 09:54:35 - 0800, Carlos Cordeiro <[log in to unmask]> wrote:

Hi,

Can anyone explain me what is ecc RAM. Is it a parity bit ?
thank you.

ECC is an acronym for Error Checking and Correcting. ECC is used in several areas of computer operations. ECC is similar to parity. However, where parity can only detect errors, ECC can actually correct most errors. By correcting memory errors, mission critical computer operations can continue.

ECC memory uses extra bits to store an encrypted code with the data. When the data is written to memory, the ECC code is simultaneously stored. Upon being read back, the stored ECC code is compared to the ECC code generated when the data was read. If the codes don't match, they are decrypted to determine which bit in the data is incorrect. The erroneous bit is "flipped" and the memory controller releases the corrected data.

Errors are corrected "on-the-fly," and corrected data is rarely placed back in memory. If the same corrupt data is read again, the correction process is repeated. Replacing the data in memory would require processing overhead that 
could accumulate and significantly diminish system performance. If the error occurred because of random events and isn't a defect in the memory, the memory address will be cleaned of the error when the data is overwritten with other data. HTH. :-)

Walter R. Worth
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