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Asked: 2026-05-23T09:31:43+00:00

I have been doing some hacking for windows and came across a fact when

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I have been doing some hacking for windows and came across a fact when I did SIDT. When I read SIDT, I found that value of IDT limit is 0xFFF(u4096).

I was pretty surprised to find it out. I was under the impression that maximum number of descriptors are 256. Then how come IDTR limit is 0xFFF?

My system is I7 running Win 7 in 64 bit.

Thanks.

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  1. Editorial Team

    Two facts:

    • The limit is the highest legal address in the table, not the highest interrupt number.
    • An IDT entry takes up 8 bytes in x86-32. In x86-64, it doubles (to 16 bytes) in order to handle the larger addresses.

    256 * 16 = 4096. Bytes would start at offset 0 and end at 4095.

    (BTW, 0xFFF is equal to 4095, not 4096.)

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