On Fri, 17 Aug 2001, David Christensen wrote:
> > > Ryan Mack proclaimed:
> > > > is running. If the system is physically compromised,
> > there is little way
> > > > I can think of to take root without having to at least reboot the
> > > > computer, thus destroying the unencrypted contents of RAM.
> > >
> > > This is a myth. RAM survives rebooting, even after a quick
> > power cycle
> > > most cells will probably still be ok. And with todays
> > memory sizes, it
> > > would take a noticable amount of time to initialize all of
> > it to a given
> > > value, so most systems don't do it (just testing some bytes of every
> > > megabyte instead).
> > >
> > > Holger
> > > -
> >
> > Errrm no. All BIOS that anybody would use write all memory found when
> > initializing the SDRAM controller. They need to because nothing,
> > refresh, precharge, (or if you've got it, parity/crc) will work
> > until every cell is exercised. A "warm-boot" is different. However,
> > if you hit the reset or the power switch, nothing in RAM survives.
>
> Most modern firmware does NOT clear memory during POST, it takes too long.
> Certain compatibility areas are usually cleared (such as the 1st megabyte)
> but the rest is
> left as is, except for a few read/writes (usually on a megabyte boundary).
> The
> exception to this rule is ECC systems. They have to be written to make sure
> the
> ECC information is correct.
>
> SDRAM memory sizing is usually done by reading an EEPROM on the SDRAM DIMM.
> The BIOS doesn't need to guess the correct timing values, it simply reads
> the EEPROM and programs the memory controller. In the case of a BIOS that
> doesn't use EEPROM you might lose data as the BIOS iteratively tries
> different memory timings and tests if they work.
>
> I have done work implementing ACPI S3 (suspend-to-RAM) in DOS by simply
> hitting
> the RESET button and restoring the memory controller settings. The contents
> of
> RAM have always been valid.
>
> David Christensen
>
I just posted working SDRAM controller initialization code. The SDRAM
controller must be initialized in a specific step-by-step manner or
else you don't even get to "restoring the memory controller settings".
Cheers,
Dick Johnson
Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).
I was going to compile a list of innovations that could be
attributed to Microsoft. Once I realized that Ctrl-Alt-Del
was handled in the BIOS, I found that there aren't any.
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This archive was generated by hypermail 2b29 : Thu Aug 23 2001 - 21:00:24 EST