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What is "Keep Alive Memory" (KAM) and how is it different from RAM?

From what I read over the internet, it is kept alive even after the ignition is OFF, but isn't that what a ROM is supposed to do?

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KAM remains powered when the ignition is off due to the fact it receives power from the battery. It is the same as RAM in the sense that it is a volatile form of memory and will lose its data if power is lost, this is what makes it different to ROM which is non-volatile and does not require power to store data.

The KAM stores details about vehicle usage such a fuel tables and is reset by disconnecting the battery and allowing them to discharge.

Another useful example are radio presets, these are lost when the battery is disconnected.

This makes it far more convenient over ROM as disconnecting a battery is far simpler than connecting to the ECU and performing a wipe of the ROM.

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    So, does that mean KAM isn't at the chip level? Is it some other form of memory installed separately? – Randy Feb 10 '16 at 15:57
  • An educated guess from what i know about KAM is that it is soldered in the ECU. Sorry I cannot confirm. – James Finnigan Feb 10 '16 at 16:07
  • KAM is just RAM that has a circuit on it to use battery current to keep the contents intact. The current is so small that it doesn't effect battery state if you leave it sitting for a long time. It will eventually run down, but the battery would do that eventually even if nothing were attached. This is why it resets when you disconnect the battery. – cdunn Feb 10 '16 at 20:20
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From what I have seen, "Keep Alive Memory" can be cleared by removing power from the car by disconnecting the battery. ROM is "Read Only Memory" and is permanent at the chip level. Yes there are various kinds of ROM that can be rewritten but at the highest level the chip itself retains the contents and requires no power to do this. Keep Alive Memory requires power to keep the memory contents.

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