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A comment on Virtual Memory Tricks. Parent comment

Re:Virtual Memory Tricks by IcePic on Tuesday November 07, 2017 @07:56AM (#15642940)
Amiga programming manuals were very clear about not (ab)using the top 8 bits even if the A1000/500/2000 were only equipped with 24 physical pins for memory (limited to 16M), so of course Microsoft Basic for amiga used the upper bits, and when the 68020+ cards arrived, it broke since the upper 8 bits actually pointed somewhere.

What is inconceivable today, will be reality at some point.

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Re:Virtual Memory Tricks by dfox on Tuesday November 07, 2017 @01:55PM (#15646329)
On amd64 (and IIRC also Alpha) hardware checks that unused bits of address are all equal to highest used bit (or IIRC all zero on Alpha) to discourage this kind of tricks.

And I vaguely remember that ESA/390 is actually 32bit address architecture in hardware and it's 31bitness comes from using highest bit of address as a flag that such tricks are taking place.

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Re:Virtual Memory Tricks by bonzini on Tuesday November 07, 2017 @08:23AM (#15643107)
The same happened for Mac OS.
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