Can RAM data remain alive over small intervals of time

Question

I experienced a very interesting phenomenon for a few days.

The setup is as such: 10 year old PC with 1GB DDR2 RAM and 80GB HDD.

Observation: I do a live boot from a CD (Knoppix). Now I shut down and start the PC again. When I start it from the live boot, it presents grub. NOW, just before the X server begins to function (before the pointer appears), I see an incomplete screenshot of my last boot workspace for a fraction of a second.

My first conclusion (obvious): This is due to SWAP space (I use Linux on my PC)

My next step: I pull out the hard disk.

New observations: Same as before!

So here's the Question: Is it possible that some data stays in the RAM even after it is powered down? I don't understand how this can be possible since the RAM should discharge in a few milliseconds after shutdown. Any ideas?

Answer 1

Memory holds data without power for a while. Typically, the BIOS would clear the memory to begin with, but video cards are not that skimpy, as the first screen will overwrite it anyway. This is a known issue in high-security areas,

In normal environments, that time would be mere seconds or less; but depending on temperature, it can be extended a lot.
There is a famous example of cracking a locked iPhone by putting it in the freezer, and then - within about 40 seconds - removing the memory chips and inserting them in a new board which provides power. You can then read what is on the memory chips. Google it.

Answer 2

Your PC will not lose all power "milliseconds" after shutdown. Shutting down doesn't even turn the PSU completely off (not if it's ATX or newer anyway).

The capacitors can actually hold a charge for many seconds after removing all power from the system (ie: unplugging it from the wall).

It sounds like your video RAM, not system RAM, isn't being cleared before being referenced again. Which isn't unheard of for discrete video adapters.