Some of the SIMMs that are used in the Macintosh IIx will not work in other
systems (Macintosh II, Macintosh SE, etc). They have "030 ONLY" stamped on the
back.
They don't work in other Macintosh systems because the CAS/RAS signals are
reversed (timing-related) from previous SIMMs.
This difference is handled in the Macintosh IIx with additional ROM code.
Those SIMMs that are marked for "030 ONLY" will work only in the Macintosh IIx
(and any future machines that use the 68030 processor).