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Nov 25th, 2008
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How to Switch into Protected Mode

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I need to make modifications to BIOS code which runs at PowerUp or Boot time and I need to access more than the lower 1,048,576 bytes of memory.

Is it possible to switch into Protected Mode at this time in order to access more memory? If so, how? What is the instruction sequence?

Alternatively, can anyone suggest a different approach?


Thanks,
Bob.
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Re: How to Switch into Protected Mode

Perhaps you should begin by describing why you need the extra memory. Perhaps we could tell you about an alternative which uses less memory.
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Re: How to Switch into Protected Mode

Click to Expand / Collapse  Quote originally posted by Salem ...
Perhaps you should begin by describing why you need the extra memory. Perhaps we could tell you about an alternative which uses less memory.
It's not that I need extra memory. What I want to do is read several bytes of data from the upper end of the 4GB address space, where an MD5 message digest of the bios will have been stored.

The intent is to compare the current MD5 with the pre-stored value to ensure that the BIOS has not been tampered with.
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This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.
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