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what r the time that result to lose data from RAM when power off

 

Without battery backup, it's just a matter of seconds. But, when shutting down and restarting a computer, give it about thirty seconds to clear the RAM totally.

There is a special class of RAM called NVRAM (Non-Volatile Random Access Memory) that retains its data on power-down, either through a battery or by using EEPROM (Electrically Eraseable Programmable Read-Only Memory) technology. You won't find it in typical computers other than in the CMOS chips.