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Message |
Guest
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 Posted:
Fri Sep 23, 2005 4:15 pm Post subject:
PC reset button resets memory? |
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When the reset button is pressed on a standard x86 PC, the processor is
reset and begins executing in the BIOS at 0xFFFF0, but is main memory
affected at all by the reset?
On modern Intel and AMD processors, does reset clear the L1 and L2
caches?
Also, the BIOS assumes that main memory is uninitialized and will begin
hosing it, but at the point that the BIOS loads the disk boot sector
and jumps to it, all physical memory above 1MB remains untouched,
right? |
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Anthony J. Albert
Guest
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| Posted:
Sat Sep 24, 2005 12:15 am Post subject:
Re: PC reset button resets memory? |
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On 23 Sep 2005 07:55:49 -0700, andrewspencers@yahoo.com wrote:
| Quote: | When the reset button is pressed on a standard x86 PC, the processor is
reset and begins executing in the BIOS at 0xFFFF0, but is main memory
affected at all by the reset?
|
No... except that as the processor restarts, the BIOS will have it
re-write a number of memory locations - setting up stacks, etc., as it
looks for an OS and loads the boot loader. The BIOS memory check, to
see how much memory is in the system, may also tweek the contents of
the RAM.
| Quote: | On modern Intel and AMD processors, does reset clear the L1 and L2
caches?
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I would assume that they are effectively "cleared", or rather, written
over, pretty quickly, as the BIOS is loaded.
| Quote: | Also, the BIOS assumes that main memory is uninitialized and will begin
hosing it, but at the point that the BIOS loads the disk boot sector
and jumps to it, all physical memory above 1MB remains untouched,
right?
|
Most likely, and even then, much of the main RAM will likely remain
untouched, even during a reboot. Shouldn't be too hard to find a
debugger that will let you examine memory, perhaps in DOS mode, to do
some quick testing.
Anthony Albert |
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Alex Colvin
Guest
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| Posted:
Sat Sep 24, 2005 1:13 pm Post subject:
Re: PC reset button resets memory? |
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| Quote: | When the reset button is pressed on a standard x86 PC, the processor is
reset and begins executing in the BIOS at 0xFFFF0, but is main memory
affected at all by the reset?
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Don't forget that the most common reason for reset is, in fact, to
get rid of a corrupted memory/processor state.
--
mac the naïf |
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Guest
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| Posted:
Sat Sep 24, 2005 2:00 pm Post subject:
Re: PC reset button resets memory? |
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Anthony J. Albert wrote:
| Quote: | On modern Intel and AMD processors, does reset clear the L1 and L2
caches?
I would assume that they are effectively "cleared", or rather, written
over, pretty quickly, as the BIOS is loaded.
Wouldn't dirty pages be flushed to main memory rather than simply being |
discarded to make way for new pages as the BIOS is loaded? They'd be
flushed on a system with an L2 cache on the motherboard rather than on
the processor chip, since the cache doesn't know or care about resets
and processor modes, and I don't see why an on-processor L2 would
behave differently. And if the L2 cache is independent of resets and
processor modes, it seems that the L1 ought to be also.
Thus it seems that on reset, only the program-visible parts of the
processor state would be lost, but data in the caches would not be
lost. Right? |
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