With the Macintosh Classic, Apple introduced a new memory expansion module
called the Macintosh Classic 1MB Memory Expansion Card. This card is
necessary to add additional RAM to a Macintosh Classic. A 2MB Macintosh
Classic comes with this card installed.
Apple's memory expansion card has 1MB of memory soldered on. In addition,
it carries two SIMM sockets to allow expansion with 150ns (or faster) 256K
or 1MB SIMM strips (Macintosh Plus or Macintosh SE SIMMs or better). Both
SIMMs must be populated at the same time with the same size RAM SIMMs in
both sockets. Either low- or high-profile SIMMs can be used. A jumper must
be changed if the SIMM sockets are used. You cannot use 4MB RAM SIMMs.
The following are valid memory configurations:
1 MB - Using 1MB on main logic board (MLB) only
2 MB - 1MB on MLB plus 1MB memory expansion card with no SIMMs
2.5 MB - 1MB on MLB plus 1MB memory expansion card with two 256K SIMMs
4 MB - 1MB on MLB plus a 1MB memory expansion card with two 1MB SIMMs
As with the Macintosh Plus and SE, the Classic's system memory can be
extended only to 4MB. In the memory map, after the 4MB RAM space, there is
the system ROM.