The Color LaserWriter 12/600 PS and Color LaserWriter 12/660 PS printers include 8 MB on the logic board as well as two SIMM expansion slots.
The standard RAM configuration of the Color LaserWriter 12/600 PS is 12 MB, which includes a 4 MB SIMM installed in one of the two SIMM slots. The Color LaserWriter 12/660 PS printer has 16 MB of RAM, which includes two 4 MB SIMMs in both of the SIMM slots.
The memory of both Color LaserWriter printers is expandable to 40 MB using standard 72-pin, 60ns SIMMs, 2K and 4K refresh in 1, 4, or 16 MB configurations. It is possible to mix SIMMs of different sizes in the two slots.
The table below lists the possible DRAM configurations for 1 MB, 4 MB, and 16 MB SIMMs installed in the printer.
DRAM configurations for the Color LaserWriter 12/600 PS and Color LaserWriter 12/660 PS:
| SIMM slot J10 | SIMM slot J11 | Total Installed DRAM | Notes |
| 4 MB | 0 MB | 12 MB | Color LaserWriter 12/600 PS shipped configuration |
| 4 MB | 1 MB | 13 MB | |
| 4MB | 4 MB | 16 MB | Color LaserWriter 12/660 PS shipped configuration |
| 16 MB | 0 MB | 24 MB | |
| 16 MB | 1 MB | 25 MB | |
| 16 MB | 4 MB | 28 MB | |
| 16 MB | 16 MB | 40 MB | |
Note: When installing memory simms of different sizes, the larger simm always goes in slot J10.
It is important to remember, however, that you must use single-sided memory SIMMs when upgrading the printer's memory, if you intend to fill both memory slots. Double-sided SIMMs are recognized as two individual memory banks and could, therefore, cause problems when the printer attempts to address the memory SIMM in the other slot.
Important: You cannot use 8 MB SIMMS in either the Color LaserWriter 12/600 PS or the Color LaserWriter 12/660 PS printer.