This article is from the Macintosh hardware FAQ, by Elliotte Rusty Harold elharo@shock.njit.edu with numerous contributions by others.
Yes. Nine chip PC and SUN workstation SIMM's work perfectly well
in any desktop Mac that can use the equivalent eight chip Macintosh
SIMM's; e.g. a IIci works with 1x9, 4x9, or 16x9 PC 80 ns PC SIMMs
just as it does with 1x8, 4x8, or 16x8 80ns Mac SIMMs. The extra
chip on each SIMM provides a brain dead type of error correction
known as parity checking. It is unused on the Mac. Since PC SIMM's
are manufactured in higher volume than Mac SIMM's, they are often
cheaper despite the extra chip per SIMM. They're also easier to
resell.
 
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