On Thursday 04 October 2007, Hans-Werner Hilse wrote: > Hi, > > On Thu, 4 Oct 2007 15:47:53 +0200 Alan McKinnon > > <[EMAIL PROTECTED]> wrote: > > On Thursday 04 October 2007, Liviu Andronic wrote: > > > And later on: "Now one problem is > > > left. Even with normal RAM a well funded organisation can get the > > > contents after the system is powered off. With the modern SDRAM > > > it's even worse, where the data stays on the RAM permanently > > > until new data is written. > > > > Pray tell, how does RAM manage to retain data when the power is > > off? It's either six transistors or one transistor and a cap per > > cell = not persistent. > > In theory, for the one transistor and one cap case, you have a loaded > cap that will take "forever" losing its load, won't it? But in > practice, I think, that's not realistic.
Definitely not realistic - the cap is on the order of a fraction of a pF and needs to be refreshed every 50-100mS or so. Once the power is off, the cap sees a (relatively) low impedance sink and discharges rather quickly > > I don't know of any magic persistent RAM that's fast enough for use > > as main RAM. Flash disks are of course another story but you do > > appear to be talking about system RAM > > There actually are new RAM types being made for solid-state storage. > But this is in a proof-of-concept stage, I think. <side note> I for one anxiously await the arrival of solid-state disks. I have customers who simply *cannot* do backups as the backup takes longer than the available window! Disk speed is a very limiting factor > Maybe Liviu's professor had those magnetic drum memory units in mind > when saying that? In all honesty, I've heard some very very strange things from the mouths of professors over the years. We don;t really know what this person said or intended > > Anyway, cleaning memory on a power-off shut down doesn't make much > sense. However, it makes sense to clean up memory after having > critical data in it -- e.g. a reboot doesn't necessarily clean up > RAM. And I'm not sure if some mainboards even keep the RAM powered in > certain situations -- at least, they can as long as the power is not > really switched off (e.g. machine only in ATX soft-off mode). Yes, this is very true alan -- Optimists say the glass is half full, Pessimists say the glass is half empty, Developers say wtf is the glass twice as big as it needs to be? Alan McKinnon alan at linuxholdings dot co dot za +27 82, double three seven, one nine three five -- [EMAIL PROTECTED] mailing list
