Author: Stan Eisenstat
Subject: Re: [Cs323] Overall parity
Date: Monday, 12 Oct 2020, 07:16:10

    > Message Posted By: Unknown
    >
    > What does it mean for overall parity to be "bad" or "good" in array
    > parity? How can good overall parity possibly signify a double-bit error?

Assume that parity means odd parity so that the parity
bit is chosen so that the total number of 1s in its
parity group is odd.

Now flip zero or more bits.  If the number of 1s in
the group (including the parity bit) is odd, then the
parity of the group is "good"; if not, it is "bad".

If the parity is "good", then the number of bits flipped
must be even.  If that number is even and not more than
two, then it must be two (= double-bit error).

--Stan-