Numerous third party vendors offer SIMMs that seem to work fine in the
Macintosh. Although we don't specify the technical requirements of
third-party SIMMs, many of those suppliers have either obtained Apple's
specification or determined our system requirements, designing their chips
accordingly.
Many of these vendors may be located by searching in Macintosh
periodicals.
IBM is another computer manufacturer that is using SIMMs in their PS2s.
Some differences are:
Parity Checking Basic Configuration Speed
_______________ ___________________ _____
IBM yes 256Kb x 9 variable
1Mb x 9
Apple no 256Kb x 8 120,150ns
1Mb x 8 120ns
A SIMM that provides for parity checking doesn't EXCLUDE that RAM from
being used in a Macintosh. Such SIMMs could be used if all other timing
and pinouts were compatible, since the Macintosh will merely ignore that
extra line.
Apple engineers have experimented with 2 IBM Model 30 256Kb x 9 SIMMs in
a Macintosh Plus, and although the testing has not been extensive, these
SIMMs have functioned using routine applications -- Excel, HyperCard,
Microsoft Word, etc. -- and have passed a short and extended memory test.
However, just because these SIMMs appear to work doesn't mean that Apple
can endorse the use of "IBM" SIMMs in our systems. IBM suppliers and PS2
third party vendors use differing RAM and designs to meet PS2's
requirements, not ours.
Also, "IBM" SIMMs are available in a variety of speeds, including: 80,
100, 120 and 150ns. The 150ns chips should definitely NOT be used in a
Macintosh II which requires at least 120ns SIMMs.
SIMM size:
- Apple currently uses surface mount technology (SMT) RAM, but there
shouldn't be a problem using DIP through-hole chips. DIP chips tend to
stand a little taller than SMT chips; but as long as they aren't so tall
that they interfere with other SIMMs, they should work fine.
Another consideration is the height of the board itself: it must not be
so tall as to interfere with expansion cards in a Macintosh SE (if any),
or the chassis in a Macintosh Plus. However, there ought to be plenty of
vertical room in a Macintosh II.
(NOTE: Apple LaserWriter SIMMs are physically and electronically
incompatible with Macintosh SIMMs.)
For more information, search under: "SIMMs"